Final Report Summary - SEAFRONT (Synergistic Fouling Control Technologies)
Executive Summary:
In summary, in the SEAFRONT project an alternative strategy for antifouling was developed, combining two concepts:
1. Combinations of multiple (novel) approaches/technologies into one coating solution rather than considering single technologies in isolation;
2. Considerable improvement of the fundamental understanding of biofouling and biocorrosion mechanisms so as to feedback and inform intelligent technology and advanced test method development.
Both concepts have been explored in this project through a process of parallel interdisciplinary studies combining, biology, genomics, biotechnology, chemistry and advanced surface characterisation techniques. This synergistic approach has ultimately resulted in the down-selection of promising technology combinations for which, after formulation and scale up, the antifouling performance was benchmarked in end-user field trials. The outcomes show outstanding research results, based on which in total 19 key exploitable areas that have been identified for further development.
By developing environmentally benign novel fouling control coatings with reduced drag, SEAFRONT has proven to significantly contribute to increase the efficiency and competitiveness of both mobile and stationary maritime structures by reducing operation and life-cycle costs. As 50% of the operational costs of a transport vessel are costs of fuel, only 5% reduction of drag, as was targeted in this project, was successfully achieved. This will already save $3 billion fuel costs and 20 million metric tons of CO2 emissions.
Extending the operational life span of fouling control coatings will save maintenance/operation costs for mobile and stationary maritime structures. Nowadays cost of ownership/operation of a container vessel includes $450,000 per scheduled repair period, which includes dry docking and other maintenance costs. Lower the frequency and time of dry docking for renewal of antifouling coatings can reduce cost of operation significantly. Bluewater expects that novel fouling control coatings will lower the maintenance costs of marine energy devices by approximately 40% since frequent cleaning at sea, lifting of the device out of the seawater to clean it (downtime) and expensive underwater inspections will become obsolete.
Furthermore, SEAFRONT has contributed to the EU Marine Strategy Directive by have established a framework for the necessary actions to be taken in order to achieve and maintain a good environmental status in the marine environment by year 2020. The Directive states that marine strategies shall be developed and implemented in order to:
a. Protect and preserve the marine environment, prevent its deterioration or, where practical, restore marine ecosystems in areas where they have been adversely affected.
b. Prevent and reduce inputs in the marine environment with a view to phasing out pollution as defined in Article 3(8) of the Directive, so as to ensure that there is no significant impact on or risks to marine biodiversity, marine ecosystems, human health or legitimate uses of the sea.
Project Context and Objectives:
The SEAFRONT project’s aim was to significantly advance the control of biofouling and reduce hydrodynamic drag by integrating multiple technology concepts such as surface structure, surface chemistry and bio-active/bio-based fouling control methodologies into one environmentally benign and drag-reducing solution for mobile and stationary maritime applications. In parallel, a combination of laboratory-based performance benchmarking and end-user field trials has been undertaken in order to develop an enhanced fundamental/mechanistic understanding of the coating-biofouling interaction, the impact of this on hydrodynamic drag and to inform technology development and down-selection of promising fouling control solutions. This project’s aim was to facilitate a leap forward in reducing greenhouse gas emissions from marine transport and the conservation of the marine ecosystem by adopting a multidisciplinary and synergistic approach to fouling control.
The overall objectives of the SEAFRONT project were:
1. Cost-effective coatings solutions with reduced environmental footprint as determined by comparative life cycle and eco-efficiency assessment
2. 50% improvement in biofouling deterrence (% coverage) and/or biofouling release (% release at a given speed over time) as compared to latest state of the art commercial reference controls.
3. Hydrodynamic drag reduction resulting in a consequent 5% improvement in operating efficiency as compared to that offered by Intersleek® 900.
In parallel, as an integral ethos within the project, a strong fundamental/mechanistic understanding and new performance predictive test methods have been developed to feedback and inform technology evolution and down-select promising coating solutions for end-user field trials.
In WP1 we have explored the technology concept of surface structure-based biofouling control strategies. This concerns strategies of which the working principle is based on surface properties of antifouling coatings such as the surface texture, the surface energy and the surface wettability. We have worked on two different technology vectors within this concept, namely textured coatings – drag reduction coupled with an antifouling effect – and switchable coatings – antifouling coatings which respond to stimuli.
WP2 was centered around the development of materials and materials combinations which prevent biofouling based on a fouling release mechanism. The highest performance commercial fouling release coatings currently utilise fluoropolymers (Intersleek® 900). To deliver the step change in performance required of a next generation technology, a combination of the unique properties of a fluorinated system with a secondary effect was needed to deliver total fouling deterrence and release. Within this work package three main classes of materials have been developed and formulated into coatings with improved performance compared with the state-of-the-art, namely innovative zwitterionic materials with a fluoropolymer anchors, fluoro-functionalized particles used as fillers or bulking agents, and domain-structured materials based on a combination of fluoropolymers with hydrogenated polymers.
Coating formulations have been prepared from first generation polymers and particles, both of which have been developed and optimized upon feed-back of their performance evaluation which has been assessed in WP4 and subsequently has led to iterative preparation of polymers, particles and coating formulations with a progressive enhancement in overall performance.
WP3 was dedicated to the development of fouling control coatings utilizing generally non-toxic, environmentally benign bioactive compounds. Where active substances are employed, WP3 was clearly focused on minimizing the environmental impact of these substances by developing non-release strategies. Given that the market for antifouling coatings is however currently dominated by releasable biocidal technologies some comparative investigation of controlled release has been performed in order properly benchmark antifouling efficacy.
WP4 has delivered high-throughput, iterative evaluation (biological/chemical/physical, including hydrodynamics) of surfaces/coatings for physico-chemical and hydrodynamic characteristics, and antifouling/fouling release efficacy in lab-scale tests. This has served to down select surfaces/coatings for field testing and provided a preliminary assessment of mechanism of action. More in-depth analysis has been done on selected surfaces/coatings as well as model surfaces prepared for hypothesis-driven experiments to improve our mechanistic understanding of biofouling and its control. In addition to the wide-ranging biological, surface analytical and hydrodynamic testing methodology established in WP4, new testing methods have been developed and molecular biology techniques, including next generation DNA sequencing, have been utilised to provide beyond state-of-the-art mechanistic understanding of biofouling and biocorrosion.
WP5 has served to evaluate the performance of solutions developed within the technology work packages (WP1-WP3) and which have been down selected based on anti-fouling, anticorrosion and hydrodynamic performance within WP4, in their intended working environment via:
• Creation of a set of defined product and application requirements for each end-use(r)
• Formulation of the technologies
• Deployment of down selected technologies and evaluation of the performance
• Evaluation of the environmental and economic footprint of technology scale-up, implementation into service and through life impact of in-field demonstrated technologies
• Scaled up manufacture of the successful technologies to volumes suitable to conduct full scale end-user trials.
• Full scale trails for end-user markets (shipping, off-shore, renewable energy, aquaculture).
In WP6 the scalability and fitness for purpose was demonstrated on an industrially and commercially viable level of the prototype technologies developed within WP1-3, down selected in WP4 and shown to have in-service and in-situ performance within WP5. This has been delivered by means of cost effective scale-up of production to industrially relevant volumes and application of this scaled up material to commercial infrastructure operated by the relevant end-users.
WP7’s prime objectives were dissemination, standardisation and exploitation of project results.
WP8 deals with the management of the EU work according to the rules and regulations laid down in the Grant Agreement closed between the EC and the consortium and the coordination of work with SEAFRONT. The project management concerns the coordination, administration, financials, contracts and intellectual property management of the project.
Project Results:
WP1 (Surface structure based biofouling control technologies)
The approach of WP1 was based on the “surface structure” of coatings, which concerns antifouling strategies where the working principle is based on the surface properties of coatings such as the coating texture, elastic moduli, surface energy and wettability. The aim was to develop environmentally benign coatings that are both effective in biofouling control and in reducing the hydrodynamic drag. Three different routes where explored. In the first route coatings were developed with a so-called shark-skin riblet structure for drag reduction and a fouling release formulation for biofouling control. In parallel detailed computer simulations were performed to study the hydrodynamic behavior of a new type of riblet structure, the so-called herringbone riblet, which is inspired by the surface texture of bird feathers. In the second route a theoretical/numerical study was devoted to the interaction between a turbulent boundary-layer flow and a compliant (viscoelastic) coating. In the third route switchable coatings where developed that can change their surface wettability and texture in response to a change in water temperature and shear stress, respectively. The idea is to use this principle for biofouling control by preventing settlement and/or enhance fouling release performance. Below the main results of the different routes will be highlighted.
Development of riblet coatings with fouling release formulation
The first months of the project were dedicated to investigations how the riblet embossing technology of Fraunhofer IFAM needs to be adapted in order to be compatible with the elastomeric fouling release coating system Intersleek® 1100SR. Samples of the standard formulation of Intersleek® 1100SR could not be used directly with Fraunhofer IFAM’s riblet producing procedure. Interaction between the resin, the solvent and the mould caused poor sample removal resulting in unacceptable pattern fidelity. Two alternative nearly solvent free formulations were developed one with only the solvent removed (causing a viscosity increase) and the second with solvent removed and adjustment of the thixotrope package so as to maintain the viscosity comparable with that of the standard paint. Both examples are thermoset coatings where crosslinking is brought about by catalyst initiated condensation cure. Only the embossing trials with the first solvent free formulations appeared to be successful, resulting in a generally good riblet quality with sharp ridges.
With this modified methodology several prototype samples (referred to as Modified Intersleek® Riblets) have been prepared for hydrodynamic and antifouling testing in WP4: coated Taylor-Couette cylinders and flat Plexiglass plates were send to TU Delft for hydrodynamic testing, and microscope slides and PVC samples were send to, respectively, UNEW-MST for barnacle and diatom screening assays, and slime farm + field testing by IP. The results from the hydrodynamic and antifouling testing are very promising, showing indeed similar drag reducing performance of the Modified Intersleek® Riblets as for the standard (non-antifouling) Dual-cure Riblets of Fraunhofer IFAM, while (after exposure to flow) the antifouling tests showed similar performance compared to the smooth (non-textured) Intersleek® 1100SR. A paper has recently been written on the results and is expected to be submitted soon to Biofouling, one of the leading scientific journals on biofouling research.
The development of the Modified Intersleek® Riblets is one of the key exploitable results of the Seafront programme and has a promising potential for use on moving vessels. Furthermore, the Modified Intersleek® Riblets are 1 out of the 3 coatings that have been chosen for down-selection and further field testing in WP5.
Numerical studies of the hydrodynamic behaviour of (herringbone) riblets and compliant (viscoelastic) coatings
TU Delft performed fully resolved numerical simulations (DNS) for flow over (possibly) drag-reducing surface textures, namely textures with riblets arranged in either a parallel or a herringbone pattern. Our simulations suggest that the herringbone texture is not drag-reducing.
Further research focused on the use of compliant coatings for turbulent drag reduction. The deformation of a compliant coating in a turbulent flow was determined from an analytical model, which showed reasonable agreement with experiments performed at TU Delft in another PhD project. The model can be used to estimate for which flow and coating parameters the coating deformation is so large that an interaction with the flow can be expected. However, the model does not capture the interaction itself, so it cannot predict whether the interaction will yield a drag reduction or increase. Future investigations should address this interaction when assessing the use of compliant coatings for drag reduction.
The results of the riblet study have been published in Journal of Turbulence and we will submit soon (February 2018) another paper to Journal of Fluid Mechanics on the deformation of a compliant, viscoelastic, coating under a turbulent flow.
Development of thermo and stress-responsive coatings
This line of research was conducted by 2 different groups in separate subprograms.
Research at UNEW-SCL
Thermoresponsive, tunable LCST (lower critical solution temperature) hydrogel materials based on oligoethylene glycol methacrylate methyl ethers have been shown to be highly resistant to marine biofouling (B. Amphitrite barnacle cyprids, N. perminuta diatoms and marine bacterial/diatomaceous ‘slime’). These promising results suggest further investigation of such materials to be of significant interest. Polymer brushes based on analogous monomers performed less well than the hydrogels and were significantly more challenging to produce. Physiochemical characterization of these materials has shown them to be highly solvated with well-defined thermoresponsive behaviors and measurement of the surface properties has allowed correlation with anti-biofouling performance. Apparatus has been developed to allow measurement of the fouling release properties of these coatings to be established under flow conditions upon transition through the coating LCST.
We prepared a series of coatings based upon poly(oligoethylene glycol methacrylates) which display near-identical chemical functionality but differ in their cloud point temperatures. All of these coatings did not undergo significant settlement with barnacle cyprids or diatoms below their cloud points (i.e. even before they were switched), making it hard to evaluate if the thermoresponsive nature of the coating actually would have any benefit. This result does, however, indicate the encouraging performance of poly(oligoethylene glycol methacrylate)-based coatings. To better test the performance of our polymer coatings as their temperatures were modulated under flow conditions, we constructed a heating platform for use with the Newcastle flow cell. Samples were fouled with diatoms and placed upon the heating platform, however a preliminary experiment indicated that no improvements to their fouling release properties were observed under flow. It is possible that further experiments exploring more extended heating/cooling cycles might reveal an improvement, but the complexity of these experiments coupled with instrumental problems meant no further work could be completed. In summary, no convincing evidence could be found to suggest thermoresponsive polymer coatings present benefit in fouling release studies, although further work would be recommend to better explore the possibility.
Research at TUE
A wide variety of micro-structuring techniques were explored in combination with both non-fluorinated and fluorinated polymeric coatings with an emphasis on anti-fouling and drag reduction. Coatings with a dynamic surface relief structure were explored and it was shown that complex relief structures can be produced which switch to a flat state in response to external triggers such as temperature and PH.
Fluorinated coatings based on crosslinked and/or thermoplastic polymers were also investigated and it was shown that micro-structures suitable for anti-fouling and drag reduction or combinations thereof can be produced. The micro-structuring can be performed with processes that use (i) mask exposures and UV-light and (ii) processes employing thermal embossing/imprinting. In all cases, it was found that on-reactive fluorinated species (so-called lubricating oils) are required to generate anti-fouling levels which are comparable to the bestcommercial alternatives. A range of micro-structures can be obtained with the appropriate dimensions and accuracy for both anti-fouling and drag reduction.
A substantial effort was devoted to identifying materials and processes that can be used on a large scale at a low cost. It is argued that rubber-like thermoplastic (co-)polymers with specific lubricating oils processed via imprinting/embossing are an excellent alternative to the currently used crosslinked systems especially if further optimization occurs with respect to adhesion to substrates and anti-fouling.
In conclusion, structure-property relationships were established for a wide variety of static and dynamic relief structures and new processes were explored for their low cost and large scale manufacturing. We anticipate that the above-described results generate new generations of drag reduction and anti-fouling coatings which, in the not too distant future, will have a positive impact on the protection of our marine environment.
WP2 (Surface chemistry based biofouling control technologies)
The approach of WP2 was based on the “chemistry of the surface”, aiming at developing new solutions to get fouling release coatings hopefully more effective than the benchmark, identified as the commercial coating Intersleek® 900. This means modification of the surface by application of a coating layer (in principle smooth) which has an innovative chemical composition acting effectively in a fouling release type manner.
The initial program of this WP was made of several tasks, which represent different routes, each one involving a specific chemistry to build-up the active ingredient of the final coating formulation.
The know-how relating to fouling release coatings before this project suggested to explore three main promising technologies, which can be identified as: i) zwitterionic materials; ii) innovative (nano)particles; iii) ultra-lubricious surfaces.
Zwitterionic materials
A zwitterion is a molecule having at least two functional groups, one positively charged and the other negatively charged, being the overall charge of the molecule zero. Zwitterions have been included in this project because in the literature some zwitterions are reported to have a significant anti-fouling behavior.
We attempted two approaches following this route, the first one employing only hydrogenated zwitterions, the second one which tried to combine the zwitterion with a fluoropolymer (more specifically a perfluoropolyether (PFPE) ) in order to keep physically grafted the zwitterion to the coating surface and hopefully resulting in a synergistic performance effect.
The first approach was pursued by UNEW-SCL, which used a specific technique to chemically graft on a glass surface commercial zwitterionic monomers (carboxybetaine and sulfobetaine methacrylates) or mixtures of positively or negatively charged monomers. After grafting different combinations of these monomers, this modified surface was evaluated (by UNEW-MST in WP4) using two biological tests on the lab scale (the diatom settlement assay and the barnacle cyprid settlement assay). Preliminary results of the biological assays showed very similar anti-fouling properties for the coatings independently from their content of zwitterionic monomers. These results were confirmed by additional tests, which concluded that the incorporation of the carboxybetaine methacrylate into the hydrophobic coating does provide only a minor enhancement of the anti-fouling properties, whereas the sulphobetaine does not provide any significant effect. Better results were obtained with the negatively or positively charged monomers: coatings having an excess of charge showed an improved performance in the biological assays.
However the relatively scarce performance combined with the difficulty to scale up this grafting methodology in the end did not justify any scale-up or field trials of this route.
The second approach relating to the PFPE-zwitterionic conjugates was developed by SOLVAY and UNEW-SCL for the synthetic part and by IP for the formulations. Several prototypes were prepared using different functionalization approaches, the most of them containing zwitterionic groups chemically linked to the chain ends of a PFPE molecule. Overall, 29 PFPE-zwitterionic conjugates were delivered to IP, which tried to incorporate such materials into coating formulations (one based on PDMS and the other one on a polyacrylic resin). In the end they succeeded to formulate 12 prototypes (of the 29) at 10% loading in the resin matrices.
The biological tests revealed that these coatings have a moderate performance, except two of them which showed very promising results when formulated in the PDMS resin. In particular fouling release performance (tested by a biofilm release test) resulted comparable to the commercial Intersleek® 1100SR, thus outperforming the Intersleek® 900 considered our benchmark.
Unfortunately these last results arrived lately, after the decision of which prototypes to be scaled-up for field trials had been made (EB meeting in Coimbra, February 2, 2017, during the sixth Progress Meeting of the Seafront Project). Therefore these zwitterionic prototypes were not tested on field trials within the project, however in the end they were classified as one of the key exploitable results and one of the promising outputs of the project.
Fluoro-functionalized particles
The basic idea of this second technological approach was to add suitable (nano)particles to standard coating matrices in order to improve the performance of the coatings in terms of fouling release properties.
The first approach consisted in the addition of hydrophobic and hydrophilic silica (nano)particles: such particles should deliver improved mechanical properties to the coating (e. g. PDMS), but, being functionalized on the surface, they should deliver also improved fouling release properties.
The synthesis of the hydrophobic (nano)particles was a collaboration between SOLVAY and Fraunhofer IFAM: SOLVAY synthesized several different PFPEs bearing one or more reactive silane functional groups, which were used by Frauhofer to incorporate the very hydrophobic PFPE chain on the surface of the silica (nano)particles. On the other hand Fraunhofer IFAM used a similar technique to prepare PEGylated (nano)particles, i. e. hydrophilic silica (nano)particles having on their surface PolyEthyleneGlycol chains.
The preparation of the (nano)particles was successful: Fraunhofer IFAM demonstrated to have chemically linked the PFPE or the PEG chain onto the surface of the particles and measured an average size of about 100 nm or less. However, when IP tried to formulate these particles in the two resins mentioned above (PDMS and polyacrylic), they faces serious dispersibility problems. In fact, even using High Shear Dispersion techniques they observed a high degree of agglomeration of the particles which produced a high level of roughness to the surface of the cured films. Contact angle measurements revealed a hydrophobic behavior for all coatings, even those containing the PEGylated particles, which is probably due to the bad dispersion of the particles.
During the last year of the project Fraunhofer IFAM tried to follow a slightly different approach consisting in adding to the silica (nano)particles other larger PTFE particles in order to achieve a hierarchical structure of particles in the coating matrix. This approach seemed to improve dispersion of the particles in the PDMS matrix and tunable surface effects were observed. Immersion tests on these prototypes started in July 2017 at the Fraunhofer IFAM site for static immersion tests, where nylon nets were also treated with some of these prototypes. Results after six months seem promising, but more time is needed to give a final assessment.
In summary this route was not selected for field trials, but it is considered among the possible exploitable results of the project.
The second approach with (nano)particles was based on fluoropolymer latexes, i.e. water based dispersions containing stabilized fluoroelastomeric (nano)particles. These latexes originate from the microemulsion polymerization, a proprietary SOLVAY technology used to synthesize fluoroelastomeric polymers. These latexes were taken in consideration with the idea to develop water based coatings. Blends have been prepared by IP with water-borne polyurethanes and acrylics. The most promising results have been given by polyurethanes: surface analysis showed some indications that surface enrichment was taking place. However the activity on this class of water based coatings was limited and final conclusions are not possible. These results could be the base for future developments when sustainability of the solvent based formulations will be seriously endangered.
Domain-structured materials creating ultra lubricious surfaces
This last route is based on the modification of the coatings with fluoropolymers, which could deliver outstanding fouling release properties. This attribute of fluoro-modified polymers is well known in the art, even though only some chemical architectures and compositions are effective and no rules are available how to select such formulations. Being fluoropolymers very incompatible with hydrogenated resins, the morphology of the coating at the nano-scale will be presumably domain-structured and hopefully should create a ultra-lubricious effect.
Two approaches were followed: a first one consisted in chemically linking the fluoropolymer to the hydrogenated resin, whereas the second one is a physical dispersion of the fluoropolymer.
According to the first approach, several PFPE bifunctional derivatives were prepared by SOLVAY and delivered to Fraunhofer IFAM and IP. The functional groups of these derivatives were: hydroxy, amine, epoxy. Fraunhofer IFAM made many formulations introducing in small amounts (low relative weight percentage) the functionalized PFPEs into different polymers like polyurethanes, polyesters and epoxy. Of the 49 coating systems prepared, eight were selected for the biological tests, which gave moderately positive results for only one formulation. IP tried to use mainly the PFPE diol in polyurethane polymer compositions, but did not succeed to obtain good performance results.
Based on these poor outcomes this technology was not selected for field trials.
Instead, much more promising results were obtained with the second approach, using a fluoropolymer by SOLVAY commercially known as Tecnoflon®. This material is a co-polymer of fluorinated and partially fluorinated olefins, which becomes after cross-linking a fluoroleastomeric rubber (FKM) with very high chemical and heat resistance, which is used in demanding applications that cannot be reached by the hydrogenated rubbers.
The polymer prior cross-linking is a solid plastomeric material, with glass transition temperature well below room temperature and slight solubility in polar organic solvents, such as ketones. Several grades of this material have been provided to IP, which tried initially to use them as physical additives in hydrogenated resin formulations. However, they soon discovered that the neat material can easily give a coherent film, and therefore they started to evaluate this polymer as a matrix in substitution of the PDMS. With this perspective they selected some formulations containing suitable PFPE derivatives, which gave very promising results in the biological assays.
Therefore this Tecnoflon® based technology was selected as one of the prototypes to scale-up for field trials.
Panels were prepared and assembled on the Royal Princess for evaluation during summer/fall 2017. Data acquisition is still ongoing.
WP3 (Bio-based and bio-active biofouling control technologies)
WP3 was dedicated to the development of fouling control coatings utilizing generally non-toxic, environmentally benign bioactive compounds. Where active substances were employed, WP3 was clearly focused on minimizing the environmental impact of these substances by developing non-release strategies. Given that the market for antifouling coatings is however currently dominated by releasable biocidal technologies some comparative investigation of controlled release has been performed in order properly benchmark antifouling efficacy.
Three different bioactive compounds were selected for investigation in Seafront:
Selektope®, an organic, non-metal compound belonging to the group of imidazoles that induces the swimming reflex of barnacle larvae and thus prevents their settlement;
Quaternary ammoniums salts (QAS) immobilized onto silica-based nanoparticles;
Chitosan, a natural biopolymer obtained by deacetylation of naturally occurring chitin.
Selektope® interferes with the normal behaviour of cyprid larvae during surface exploration prior to settlement. When larvae arrive and attempt to explore a surface, Selektope® stimulates a response which induces a deterrence effect and results in the organism swimming away from the surface. Due to its specific and non-lethal mode of action, efficacy can be achieved by incorporation of low amounts of Selektope® relative to the biocide content in traditional antifouling coatings.
Quaternary ammoniums are well known antimicrobial agents, specific compounds of which are currently under BPD evaluation for non-marine end-uses. The likely mechanism of action involves ion exchange between the positive charges on the surface and structurally critical mobile cations within the membrane. The loss of these structural cations results in a fatal loss of membrane integrity in the microorganisms.
Chitosans are polyaminosaccharides obtained by deacetylation of naturally occurring chitin. Chitosans show a broad spectrum of antimicrobial activity, which has been explained by (i) cell wall leakage by ionic surface interaction or by teichoic acid binding and extraction of membrane lipids, (ii) mRNA and protein synthesis inhibition and (iii) suppression of microbial growth through external barrier formation and metal chelation. Unlike other natural bioactives chitosan is available economically and in large quantities due to it being a by-product of the shellfish industry. Furthermore, it is rapidly reintegrated into the marine environment through natural decomposition pathways and therefore environmentally benign.
Additionally, a fourth group of compounds has been considered for surface functionalization in WP3, namely polyglycerols. Dendritic and linear polyglycerols are able to dramatically reduce the non-specific interaction of proteins with surfaces. Among the various polymeric architectures, dendritic ("treelike") and linear polyglycerol polymers have experienced an exponential development due to their multifunctional and well-defined structures. These polymers exhibit good chemical stability and inertness under biological conditions and are highly biocompatible.
For the above mentioned bioactive compounds, an environmental risk assessment was carried out. All three bioactives exhibit acceptable risk ratios in the marine environment with the exception of QAS in the sediment compartment. However, a refinement of the risk assessment based on a complete data set with regard to the required tests would likely lead to an acceptable risk profile also for QAS.
Different strategies to immobilize the active compounds on the coating surfaces have been investigated so as to create antifouling coatings that do not release any bioactive compounds into the environment. Samples have been produced with immobilized polyglycerols, QAS, Selektope®, and chitosan. These samples were characterized with regard to their surface properties and laboratory settlement assays at Newcastle University were performed for the non-toxic samples and field immersion tests for some other samples. One of the immobilization strategies focused on tethering the bioactives to a phosphate fluorofluid for subsequent incorporation into a fluoropolymeric paint matrix. The samples containing QAS fluid showed very good early slime resistance, but performance diminished rapidly presumably due to the fluid leaching out of the film. Samples with Selektope® fluid showed lower antifouling performance as compared to Intersleek® 1100SR. A general challenge in working with chitosan is the poor solubility in organic solvents and hence it was not possible to generate compatibility with this kind of approach.
The second approach to realize permanent immobilization of the active compounds to the coating surfaces was based on covalent coupling reactions. It comprised the use of QAS immobilized onto silica nanoparticles, a patented technology already commercially available for a series of other applications (http://www.matera.pt/technology/ambio/). These functionalized nanoparticles were dispersed in Intersleek® 1100SR. Samples with this experimental nanocomposite coating yielded promising results in the various biological tests, i.e. antimicrobial activity against selected bacteria strains, settlement assays with diatoms and barnacle cyprids (WP4) as well as preliminary field immersion tests. Therefore, this coating system was down-selected for benchmarking and performance evaluation in situ within WP5. Immobilized polyglycerols showed good performance in bacteria and algae tests but their stability was insufficient under seawater conditions and the effect was lost after several weeks. Selektope® is a small molecule and hence represented a specific challenge regarding covalent coupling without blocking the active site responsible for inducing the reaction in the cyprid larvae. The results from the barnacle assays suggested that the immobilization had not been successful and that Selektope® leached out of the coating sample. Lastly, immobilization of chitosan invariably led to the loss of the antimicrobial activity under neutral or slightly basic seawater conditions. Therefore, different attempts were made with modification of chitosan in order to maintain the antimicrobial properties also under non-acidic conditions. The use of water-based acidic binder systems in combination with specific aqueous acid solutions for dissolution of the chitosan yielded promising results. Since such systems are only of limited water stability they will be useful for other applications rather than antifouling coatings.
The third objective in WP3 was to develop and investigate a new generation of self-polishing coatings based on bioactive and biodegradable polymers. The underlying objective of all current self-polishing coatings is the controlled release of a toxic biocide. Within SEAFRONT, the aim was to abandon the use of toxic biocides completely and rely instead on the self-polishing effect of the biopolymers supported by the antimicrobial activity and hydrophilic character of chitosan, hydrophilicity being known to be an important parameter in inhibiting protein adhesion. The ultimate goal was the development of a coating based on a maximum content of natural biodegradable material in order to achieve the optimum benefit in terms of eco-efficiency and sustainability. Two groups of bio-based polymers were selected for this purpose: polyhydroxyalkanoates (PHA) and chitosan. Initial work focused on identifying suitable organic solvents for the two substances. This proved difficult for both substances. Albeit repeated trials also with lower molecular weights and finer particle sizes the problem could not be overcome and both compounds will most likely have to be chemically modified in order to make them suitable as polymeric binders. Therefore, an alternative approach has been investigated to use PHA and chitosan as additives in self-polishing antifouling paints. Several different formulations have been developed either i) replacing ZnO by PHA or chitosan, ii) replacing total pigments in the paint resulting in 5% PHA or chitosan in the finished paint, or each 2.5%. Initial results showed some potential synergy in using a combination of PHA and chitosan in an antifouling formulation but with longer immersion this effect seems to be decreasing. A non-toxic paint containing PHA has been tested for slime settlement and clearly outperformed all biocidal coatings over a period of over 50 days. Non-toxic chitosan and PHB containing coatings immersed in Singapore exhibited very poor performance against animal fouling. Recent work has focused on modification of PHA so as to achieve smaller molecules with better solubility behaviour and an aqueous PHA dispersion was successfully developed from which clear stable coating films could be produced.
The last objective of WP3 was to demonstrate that immobilization of a bioactive has no adverse effect on its antifouling performance. To this aim comparative studies were carried out with the bioactives being physically dispersed in a coating matrix. Results with the QAS nanoparticles indicate that the antimicrobial performance of the self-polishing coatings is inferior to the Intersleek® 1100 SR and PDMS systems functionalized with QAS nanoparticles. For Selektope® on the other hand, the inclusion into an SPC binder showed an improved antifouling performance particularly for the Selektope® fluorofluid. This corroborates the conclusion from the immobilization studies that Selektope® cannot be tethered to the coating without losing its effect.
In conclusion, the development of more eco-friendly-based antifouling coatings represented a series of challenges which could not be fully overcome within SEAFRONT. Nevertheless, very promising approaches could be identified which might be further pursued in the future.
WP4 (Characterisation, Fundamental Understanding & Performance Prediction)
The main aim of WP4 was to deliver high-throughput iterative evaluation of surfaces so that down-selection could be made for field testing. Additionally, the WP aimed to develop new testing methodologies and through fundamental studies, improve our understanding of marine biofouling and corrosion. WP4 comprised five subsections: 4.1 physical/chemical characterisation; 4.2 hydrodynamic characterisation; 4.3 biological evaluation; 4.4 test method development/refinement; and 4.5 fundamental understanding of biofouling and corrosion.
Physical/chemical characterisation
Most of the work on physico-chemical characterisation was done, as originally proposed, by partners producing surfaces in WPs 1-3. WP4 focussed on characterisation of the coatings down-selected from WPs 1-3. At UNEW, six reference coating samples: Intersleek® 700, Intersleek® 900, Intersleek® 1100SR), Intersmooth® 7460HS, Intersmooth® 7465Si and Intercept® 8000 LPP were studied, as well as surfaces developed by UNEW – a thermo-responsive polymer (polymer brush of polyethylene glycol methyl ether methacrylate (PDEGMA)) and zwitterionic surfaces. This study used atomic force microscopy (AFM) to investigate many surface properties including morphology, roughness, Young’s modulus, adhesion strength, stiffness and nanoindentation. The static contact angle of the wet coatings under water was determined by the captive bubble technique. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to study the chemical composition of the control and new coating films.
Hydrodynamic characterisation and development of new hydrodynamic testing methods
Frictional drag measurements on surfaces were made using using the Taylor-Couette (T-C) facility at TUDP and the flow cell (modified under D4.4) at UNEW. The T-C setup proved a useful tool for quick assessment of differences in the skin friction of coatings at high shear Reynolds numbers as compared to standard drag plate measurements in a water tunnel. For accurate and reproducible skin friction measurements it was essential to: (1) soak newly provided coatings in water for at least 24 hours; (2) ensure sufficient adhesion of a coating foil on the T-C cylinder; and (3) ensure sufficient sharpness of the riblet tips in case of riblet coatings. A highlight of this work was the demonstration that the modified Intersleek® fouling release coating with riblet texture, developed within WP1, exhibits the same drag-reducing performance as the standard polyurethane riblet coatings of Fraunhofer IFAM. The optimum drag reduction was about 6%.
The flow cell at UNEW was modified such that the turbulent flow experienced over the surface of a ships’ hull could be replicated. For conciseness, modifications and method analysis done in WPs 4.2 and 4.4. will be combined here.
The flow cell was improved by replacing the measuring section with a new testing section. The old test section accommodated 76 mmm x 26 mm microscope slides. While this capability was retained, the new test section, made from stainless steel, was designed to accommodate UNEW standard flat test panels measuring 600 mm x 218 mm x 15 mm. This meant that skin friction measurements could be made on coated panels that had been exposed on the strut system of the RV Princess Royal in WP5. CFD simulations were carried out for the modifications to the flow cell. These included a new contraction section with a more favourable side profile, a lengthening of the test section from 2500 mm to 2700 mm and new pressure taps along the side walls of the pressure drop section for frictional drag measurements. The CFD simulations predicted that the turbulent flow would be fully developed in the new pressure drop section. Wall shear stress measurements and the shape of the velocity profiles confirmed this. Furthermore, with a channel height of 10 mm and an inlet flow speed of 0.5 m/s, shear stresses of approx. 250 Pa were predicted, corresponding to full shear stress on hull forms in excess of 30 knots full-scale speeds. Once the modifications were completed, the pressure drop methodology was evaluated against direct boundary layer measurements using three duplicate test surfaces: hydrodynamically smooth acrylic; a fouling release coated panel; and a self-polishing copolymer-coated panel. Roughness measurements were made with Uniscan’s OSP100 laser profilometer. Boundary layer profiles were obtained using the Emerson Cavitation Tunnel (ECT) and DANTEC’s two-component fibre-optic Laser Doppler Anemometer (LDA). These were compared with the skin friction measurements obtained by the pressure drop method. Although the methods cannot be compared directly, good correlations were obtained for the reference surfaces in terms of friction velocity and skin friction coefficients up to the maximum velocity of the Emerson Cavitation Tunnel (ECT) of 6 m/s.
A comparison of the hydrodynamic performance of biofilmed (developed under dynamic conditions on the RV Princess Royal for approx. 6 months) vs. clean fouling release coatings (IntersleekS 700, 900 and 1100SR) in the form of plots of wall shear stress vs Reynolds number (Re) revealed little difference between the two conditions. The exception was IS 900 at the highest Re values (>60,000), which gave slightly lower shear stress values in the biofilmed condition. The similarity of performance in the fouled and clean conditions likely reflects an absence of clear differences in the roughness values.
While the hydrodynamic performance of clean and biofilmed commercial fouling release coatings has been completed, a combination of a move of the ECT (including shipping to Poland for renovation) from the main campus at UNEW to a new facility at Blyth Northumberland and a late decision on down-selection of prototype coatings from WPs 1-3, has meant that the hydrodynamic performance of the latter coatings has yet to be completed. Panels coated with the three selected coatings (see below) were delivered too late in the 2017 season for field exposures to acquire biofilm and will now be exposed in early spring 2018, with the hydrodynamic measurements completed in summer 2018.
Biological evaluation
Most of the biological assays for the programme were laboratory-based and performed by UNEW but some in-house assays (e.g. mussel and bacteria) were done by partners formulating the coatings. In addition, natural biofilm ease of removal data were provided by IP using their ‘slime farm’ biofilm culturing reactor and UNEW’s flow cell. IP also provided raft settlement panel data collected in Changi, Singapore, Hartlepool, UK and Bratton, Sweden.
UNEW assayed 105 coatings (including 15 control/standard surfaces) for effects on barnacle, Balanus amphitrite, cyprid settlement and initial attachment and ease of removal of the diatom Navicula incerta. Before the laboratory antifouling and fouling release assays were performed, leachates of coatings were tested for toxicity with barnacle nauplii. Any residual toxicity (e.g. from uncured components) was removed sufficient to permit barnacle settlement assays by leaching for periods of 1-7 weeks. However, Selektope®-based surfaces completely inhibited barnacle settlement and leachates from some of the Technoflon fluoro-elastomer surfaces inhibited barnacle settlement after extended leaching periods. Nevertheless, these surfaces could be assayed with Navicula.
In order to down select coatings for further testing in WP5, a means of comparing the efficacy of coatings was needed that took account of the different surfaces and different batches of organisms used on different dates. This was achieved with reference to a standard surface that had been included in all assays, namely, PDMS. The data were converted to standardized effect size measures using the ‘Hedges g’ estimator. A different standardization was used for the data supplied by IP: the performance of each test surface was divided by the performance of the standard (PDMS) tested at the same time. Coatings were then ranked based on their relative performance in up to eight of the measures, with each measure normalized on a scale of 1-100 and a median rank calculated across the measures to give an overall ranking of performance. Based on these rankings and readiness for field performance testing, three candidates, one from each of the WPs 1-3, were selected by the SEAFRONT Executive Board: WP1 - Modified Intersleek® with riblet structure; WP2 - Tecnoflon® perfluoroelastomers; and WP3 - QAS nanoparticles.
2- and 3-dimensional tracking studies
UNEW refined the existing 2-D set up for video tracking of cyprid settlement behaviour and developed a new 3-D system. The new developments in the 2-D system comprised bespoke algorithms to reliably track cyprids and automatically characterise (using two neural network classifiers) their behaviour based on body movements. For the first time, multiple cyprids have been tracked, simultaneously, over long periods (24 hrs), encompassing their entire settlement behavioural repertoire. Moreover, the original classification of settlement behaviours into wide search, close search and inspection has been confirmed with inspection events proving a reliable predictor of propensity to settle. Based on this advance in understanding, a rapid (one hour) assay has been developed to allow high-throughput evaluation of coatings. A new tracking system, using two cameras, has also been developed to calculate the position of cyprids in three dimensions (x,y and z). A user interface has been built to allow users to calibrate the two cameras. The calibration procedure produces a 3x2 matrix that defines the 3-D dimensions of the animals during their movements. Multiple cyprids can be tracked and their trajectories estimated with this system. As the interaction of organisms with surfaces was the primary consideration of this project, most use was made of the 2-D tracking and classification system. Its wider utility has been demonstrated with trials using tubeworm (Ficopomatus enigmaticus) larvae and diatoms (Navicula incerta).
Molecular biology of barnacle settlement
UGOT established a procedure for ‘capturing’ individual Balanus improvisus cyprids, from many parallel experiments, at different stages of the settlement process: i) free swimming; ii) close searching; iii) early attached; and iv) newly metamorphosed juvenile barnacles. Twenty cyprids provided sufficient RNA to generate high quality RNA-seq data. These data were evaluated to remove various types of bias, including technical bias during sample handling and sequencing and variability in gene expression linked to different batches of cyprids. This ‘pipeline’ for gene expression studies is now being applied to the down-selected surfaces from the programme in an attempt to understand the molecular basis of antifouling.
A transcriptomic approach was taken to analyse changes in gene expression during pre-settlement behaviour, attachment and metamorphosis of cyprids. Comparison of global gene expression across settlement showed that pre-settlement stages (free swimming and close search) had similar expression patterns. However, large-scale changes occurred during the transition from a pelagic to an attached cyprid and from attachment to juvenile, i.e. pre- and post-metamorphosis. Genes upregulated during pre-settlement stages included those with functions related to transferase and DNA polymerase activity, perhaps indicative of highly active cell division, juvenile hormone binding protein, which is involved in metamorphosis, and genes related to signal transduction. After attachment, genes involved in developmental processes, in particular the guidance of the spatio-temporal patterns of gene expression, were upregulated, as were several cement protein homologues.
As cyprids of B. improvisus display a preference for hydrophobic surfaces at settlement, it was of considerable interest to identify genes that may be involved in the discrimination process between hydrophilic and hydrophobic surfaces. Notable genes down-regulated by exposure to a hydrophilic surface included MFS-type transporter SLC18B1 involved in the transport of biogenic monoamines, such as serotonin, and Ras-related protein Rap-2 which is a part of several signalling cascades and may regulate cytoskeletal rearrangements, cell migration and adhesion.
Finally, 291 chemoreceptor gene candidates, expressed in cyprid antennules (the appendages involved in searching behaviour), were identified. Some of these may be involved in surface selection by cyprids. In situ hybridisation studies to localise the receptors in whole cyprids proved problematic, and work continues with tissue sections, to obviate the need for probes and dyes to penetrate the cyprid cuticle.
Biocorrosion
The aim was to investigate the protective performance of coatings (a phenalkamine-cured coating, Intershield® 300; a fatty acid-modified, polyamide-cured coating Intershield® 300HS; and a pure polyamide cured coating Interseal® 670HS) against microbiologically-influenced corrosion (MIC) and in so doing, advance our fundamental understanding of this process. Coatings were applied over mild steel (CR4 grade). The approach used by TUDM was to combine microscopic, electrochemical and microbiological analyses to evaluate coating performance after immersion in three different environments: 3.5% sodium chloride solution, artificial seawater (ASW) and natural seawater (under laboratory and field conditions). Natural seawater, with its complement of microorganisms, caused a drastic reduction in the barrier properties of the coatings compared to ASW and the NaCl solution. The polyamide coatings gave the best protection against MIC. Adhesive and cohesive failures of all three coatings were noted irrespective of the solution type. Results for laboratory exposures in natural seawater were comparable to field exposures after 30 days.
Microbial fouling
BRIS carried out metagenomic analyses of biofilm formation on three biocidal anti-fouling (Intersmooth® 7460HS, Intersmooth® 7465Siand Intercept® 8000 LPP) and three fouling release coatings (Intersleek® 700, Intersleek® 900 and Intersleek® 1100SR). Six replicates of each coating (6 x 6 painted squares in a Latin square design, controlling for distance from the edge of the wooden backing panel and depth) were immersed in Hartlepool Marina in December 2014 and biofilm was sampled over four time points between March and June 2015. Identification of colonising microorganisms was carried out using multiplexed Next Generation Sequencing of bacterial 16S rRNA gene and eukaryotic Internal Transcribed Spacer (ITS) regions. More taxa, both bacterial and eukaryotic, were present on the fouling release coatings. With respect to bacteria, principal component analysis (PCoA) revealed clustering of the samples based on coating type and time of collection; clustering was less pronounced for eukaryotes. A number of issues were recognized with this experiment including the fact that the relatively static condition of exposure is not what the fouling release coatings were designed for; assaying bacteria and eukaryotes separately may have given a false impression of their relative contribution to the developing biofilm; and neither of the marker genes effectively detected archaea. A second exposure under dynamic conditions was done with coatings (2 x fouling release and 7 x biocidal anti-fouling) applied to microscope slides in the ‘Dove Lab Flume’. Slides were immersed in September 2017 and sampled at three time points during September and October. A whole-metagenome shotgun sequencing approach was then adopted. The detailed analyses have yet to be completed but a clear difference in taxonomic abundance between the fouling release and biocidal anti-fouling coatings was detected by PCoA with higher relative abundance of archaea and eukaryotes on the fouling release coatings explaining 93% of the variance. The Intersleek® coatings could also be separated with more archaea on Intersleek® 1100SR and more eukaryotes on Intersleek® 700. Gene-level analysis (BLASTX viewed in MEGAN) revealed that differentially abundant genes across the coating types were related to taxonomic abundance.
WP5 (Benchmarking & Performance Monitoring In situ)
The objectives of WP5 was to evaluate the performance of solutions developed within the technology subprojects (WP1-WP3) and which have been downselected based on anti-fouling, anticorrosion and hydrodynamic performance within WP4, in their intended working environment.
Data from all end users was collated regarding coating requirements in terms of the minimum and desirable design elements for application, performance, product features and product usage. Given the wide variety in end user requirements such as substrate material, surface preparation, expected performance lifetime and the level of acceptable performance it is unlikely that a single product/technology developed in the project will address the needs of all end users. It is more likely that different approaches will be needed or that broad technology platforms can be customized to suit the individual needs of the end users.
Application trials (substrate adhesion and cracking resistance) was conducted using the commercial benchmarking coatings and the downselected prototypes on the substrates used by the end users in order to determine suitability for them to be deployed in-field.
For the fouling release riblets approach (Modified Intersleek® Riblets) the formulation of Intersleek® was modified to make it more amenable to a mould based texturing process. Solvent content was minimised to avoid shrinkage upon cure and to ease demoulding and the thixotrope level was adjusted to obtain the correct rheology profile. Prototype paints were formulated and manufactured to enable preparation of the field trial test coupons and textured films were produced for fouling control and hydrodynamic testing using a silicone negative mould.
Environmental data acquisition devices were designed and fabricated for the purpose of monitoring the environmental parameters during the field deployment trials. Water temperature, salinity, chlorophyll level, dissolved oxygen level, dissolved organic matter and suspended sediment level (Secchi Depth) were recorded whilst the coupons were immersed using a combination of static data loggers and Earth Observation data. Custom software was written to process the data and the database updated weekly. Loggers were similarly developed and code written to support the vessel trails where geographic position and vessel speed were additionally recorded.
Coated test coupons were been prepared for all the benchmark commercial coatings. Deployment of them serving two purposes; 1) Obtaining reference performance data on the current state of the art systems in different environments 2) Creating an opportunity to practice and improve the assessment protocols and sampling procedures prior to deployment of the project prototypes. Panels were prepared with coatings which comprise a mixture of high performance biocide free fouling release coatings and biocide containing anti-fouling coatings intended for commercial shipping (marine) end use and pleasure craft (yacht) markets
13 assessments were performed on coupons deployed in the United Kingdom, Italy, Singapore, USA and Brazil. Assessment was performed using percentage coverage using visual and multispectral routes with biofilm sampling taking place to enable calibration of the multispectral images and to collect material for the metagenomics analysis of the biofilms generated (see WP4).
Additional testing coupons were immersed at the MIN testing site in Strangford Lough, Northern Ireland, these consisted of sea bed (using a mini quad pod base) and sea surface (on the surface operating platform) deployment, corresponding to 24m and 1 m immersion depths. Custom frames were designed and fabricated from galvanized mild steel for both test locations which could accommodate multiple test coupons and were rigid enough to withstand the tidal current conditions present in the Lough. An underwater locator beacon (ULB) was used to ease divers finding the seabed frame which was periodically inspected in-situ. The seabed frame was inadvertently placed in close proximity to one of the mooring chains of the testing platform, severe scratching was seen on the coatings with no observable fouling present. It was subsequently found that the surface deployed panel has become detached from the frame during the test period, this was most likely due to failure of the wooden coupon as the frame itself appeared intact, thus no coating benchmarking data was generated.
Nylon fishnet samples were coated with 3 fouling release coatings (Intersleek® 700, Intersleek® 900 and Intersleek® 1100SR and one biocidal coating (Intercept® 8000 LPP) by IP. The nets were coated by immersion into a vat of wet paint followed by removal of the excess by squeezing and then hanging. Adhesion of all the coatings was acceptable direct to the net material and whilst the flexibility of the nets coated with the Intersleek® coatings was lower than the uncoated net they were significantly more flexible than the biocidal coated net where the flexibility was reduced to a level where it made the nets unsuitably stiff. Immersion at VAL’s mid-Norway test site was conducted using a PVC frame for mounting the nets and holding them into shape. The nets were periodically assessed by measuring the amount of fouling present once a month over a 6 month period ending in mid-October the end of the fouling season in the test area. Two cleaning tests were performed with the nets being washed with different water pressures at week 19 and week 29 with water pressures varying from 20 bar up to 60 bar, and the distance between the water jet and the net panels varying between 2 cm and 30 cm. Image analysis was used to accurately quantify the amount of organic material present with the net void space and net fibre area being subtracted to give a percentage fouling coverage. At week 28 the nets coated with Intersleek® were more or less covered with mussels with the uncoated net being more fouled than the coated ones. The nets coated with Intercept® 8000 LPP had no visible fouling.
The two different water pressures used for the cleaning tests (30 and 60 bar) correspond to 8 and 12 L of water per minute respectively. After each wash the nets were lightly rinsed with a low pressure hose to displace the unattached (cleaned) material which had become entrapped in the net during the removal cleaning step. Fouling coverage using image analysis was again used to calculate the amount of fouling present before and after each cleaning pressure. It was found that at 60 bar all the commercial coatings were superior to the uncoated net and that at 30 bar the highest performing coating was Intersleek® 1100SR.
Full scale speed-power testing was conducted using International Towing Tank Conference (ITTC) recommended standards after Intersleek® 1100SR was freshly applied to the RV Princess Royal, the UNEW catamaran research vessel. During the project instrumented shafts were installed and calibrated with measurements of shaft thrust torque and speed, fuel consumption, speed over ground and speed through water then being analysed using the ISO 15016 procedure. Software was developed to post-process the measurements (normalising process) to subtract external forces acting on the vessel (wind, wave and water quality). Periodic performance measurements have been carried out after the dry-docking to determine the effect of biofilm growth on normalised ship performance.
Three Life Cycle Impact Assessments (LCIA) have been made for the prototype coatings in three end user environments with a full characterization for each downselected system. Aquaculture, marine shipping and marine renewable energy environments were analysed with comparison being made of the environmental impact (manufacture, transport, application and water resource) for each prototype product application. An environmental score card was generated for each of the downselected routes with a complete analysis from the environmental and eco-efficiency point of view using three different quantification methods (ILCD 2011 Midpoint+, ReCiPe Midpoint (I) V1.12 / Europe Recipe I and Eco-indicator 99 (I) V2.10 / Europe EI 99 I/I.).
Along the same lines as the environmental score card the eco-toxicity of each system was measured using Disability-Adjusted Life Year (DALY) to measure the years of life lost by the people, and lived with a variety of disabilities due to diseases, potentially disappearing fraction PDF*m2 per year, which measures the number of plant species that become extinct per square meter per year and MJ of energy of more than is necessary to provide per kg or m3 of mineral or fossil fuel extracted, since it will be more difficult to get them out of the nature. The different categories shown in each case are grouped into three main areas; Human health, Ecosystem quality and Resources.
For the three downselected candidates (Modified Intersleek® Riblets, Tecnoflon® Fluoroelastomers and QAS nanoparticles) flat test coupons have been prepared and subsequently immersed by IP in Hartlepool, UK, Bratton, Sweden and Changi Singapore. In each case reference coatings were immersed alongside the prototypes to enable benchmarking of the newly developed systems.
The riblet surfaces were tested in vertical and horizontal orientations and whilst the performance of both was seen to be marginally worse than the smooth Intersleek® 1100SR reference the fouling control behaviour was much superior to the smooth PDMS control (a non-fouling release test surface). The Tecnoflon® based coatings were seen to be comparable or better than Intersleek® 700 and Intersleek® 1100SR references. The coatings made QAS nanoparticles sprayed onto the surface performed no better than the PDMS control and when dispersed into the Intersleek® 1100SR formulation performance was lower than the equivalent control with no particles.
Frames holding coated net samples were immersed at the aquaculture site of VAL located in mid-Norway. The nets were commercial fish netting cut in smaller test squares with the coatings being applied by dip coating and hanging. The Modified Intersleek® Riblets were not testing due to the nets not being appropriate for a laminate foil approach thus only the Tecnoflon® and QAS nanoparticle prototypes were tested. Photos were taken of the nets once a month during the trial period (12 weeks). At the first assessment the uncoated net samples were noticeably more fouled than the coated samples, with Intersleek® 1100SR and QAS nanoparticles having the least amount of fouling (brown and green algae) which was only loosely attached. At week 12 the Intersleek® 1100SR and QAS nanoparticles still had the least fouling, while the uncoated net samples were the ones with most fouling.
Panels for hydrodynamic drag measurements were prepared to conduct boundary layer and pressure drop testing of the three downselected coatings in a clean and biofilmed condition with the biofilm being generated under two flow regimes: firstly under low hydrodynamic shear in static condition using rafts; and secondly mounted on the RV Princess Royal’s “strut arrangement” where the high hydrodynamic shear stresses accurately mimics the true in-service conditions to be experienced by a vessel. Intersleek® 1100SR and Intercept® 8000 LPP were used as the commercial standards.
WP6 (Full scale in-situ demonstration)
The objectives of WP6 served to demonstrate the scalability and fitness for purpose on an industrially and commercially viable level the prototype technologies developed within the project via application to commercial infrastructure operated by the relevant end-users with performance comparisons to current state of the art technologies.
Two paint applications to commercial, globally active container vessels of partner HLAG have been completed. Test patches (4m width and 7m height) of three benchmarking coatings were applied to develop reference performance baselines for the commercial coatings. The coatings were applied during scheduled maintenance and repair dry dockings in China using airless spray. One vessel was emergency dry-docked in Singapore 15 months after the patch applications enabling it to be inspected. Due to scheduling the inspection could only take place at night when the visibility was poor which resulted in similarly poor photo quality; Intercept® 8500 LPP was seen to be the best performing coating. The second vessel was dive inspected in Korea 9 months after test patch applications using a CCTV and photo inspection process. Intersmooth® 7460HS was seen to be the best performing coating.
Trials have been conducted in Singapore and Hartlepool, UK using a Robotically Operated (submersible) Vehicle (ROV) to conduct vessel inspections with the aim of increasing diver safety, ease of inspection scheduling and assessment quality.
Four vessel application trails and six assessments have been conducted on high activity yachts and coastal vessels. These were chosen as they afforded easier access and greater logistical simplicity than commercial marine vessels during the application and inspection process. The increased in-dock flexibility and duration allowed more in-depth studies to take place (9 coatings being applied vs. 3, biofilm sampling, multispectral imaging). To remove interperson bias, all assessments were conducted by the same assessor and to remove preconceptions concerning coating bias all the assessments were conducted blind. A weighting system associated with each “class” of fouling (biofilm, weed, soft bodied and hard bodied) was used to deduce the fuel penalty of the accumulated fouling rather than solely using the coverage of the surface by fouling. The data associated with the four vessels from 10 inspections over a 1-2 year immersion period was aggregated and Intersleek® 1100SR was determined to be the best performing coating on 7-9 knot dynamic/static cycling coastal vessels operating in UK waters.
DNA analysis of the biofilm present on the coatings applied to the four yachts and coastal vessels after their in-service period in coastal UK waters was performed. Samples were scraped from the test patches and DNA extracted using Power Biofilm kits (Qiagen). Bacterial biofilm composition was assessed by amplifying the V3 region of the 16S Ribosomal RNA coding gene and eukaryotes with the rDNA-ITS locus.
The wing of the MIN Deep Green device was coated with a modified clear coat variant of Intersleek®. Due to the need for the decorative decals to be visible an optically clear acrylic primer and Intersleek® were used. The wing was coated on both sides using a foam roller. The nacelle parts were coated with yellow Intersleek® 1100SR.
Construction of the BLUE BlueTEC device was completed in Amsterdam in March 2015 when Intersleek® 1100SR was applied to the underwater areas. It was then deployed into the water in May 2015 at the port of Den Helder, Netherlands where it was hooked up to the shore via the power and umbilical cables. After two turbine trails (4 months for the first, 7 months for the second) the device was permanently lifted out of the water. Only biofilm was visible on the device body (coated with Intersleek® 1100SR) whereas the uncoated blades were heavily fouled with barnacles and a significant amount of biofouling was seen inside the turbine itself both of which severely reduced device efficiency.
A single vessel trial has been conducted for the downselected prototype coatings. Intersleek® 1100SR, Tecnoflon® and QAS nanoparticle based paints were applied to a trawler based in the North East of the UK in September 2017. Also applied were prefabricated film laminates of Modified Intersleek® Riblets.
The tether used with the MIN Deep Green device had patches of Intersleek® 1100SR, Tecnoflon® and QAS nanoparticles applied to it. Replicate patches were placed in various positions along the tether to enable assessment of fouling challenge and coating performance across a vertical depth transect (seabed, 5m, 21m and 26m above the seabed). The tether was deployed for a 6 month period after which is was visibly assessed and sampled for DNA analysis. The coatings in the seabed area had detached due to flexing and/or abrasion so was inconclusive, at the other three depths where the coating scheme remaining intact Intersleek® 1100SR was the best and Tecnoflon® the worst performing coating.
Potential Impact:
WP1
Joint work within WP1 and WP4 has led to 1 out of the 3 technologies chosen for down-selection and field trials in WP5: the Modified Intersleek® Riblet. The development of this coating has also been identified as one of the key exploitable results of the Seafront programme.
The Modified Intersleek® Riblet was developed in WP1 and tested in WP4 and WP5. The results from the hydrodynamic and antifouling testing of this coating are very promising, showing similar drag reducing performance of the Modified Intersleek® Riblets as for the standard (non-antifouling) Dual-cure Riblets of Fraunhofer IFAM, while (after exposure to flow) the antifouling tests showed similar performance compared to the smooth (non-textured) Intersleek® 1100SR. This has a promising potential for application to moving vessels. Field tests are ongoing at the moment. A paper on the development + results from testing has been written and will be submitted soon the Biofouling, a leading journal on biofouling research.
The numerical study at TU Delft of the herringbone riblet did not reveal a drag-reducing potential. Their research on compliant coatings was restricted to very small coating displacements such that the reaction of the compliant coating could be ignored. From this study no conclusions can be drawn about the potential of compliant coatings for drag reduction, although the modelling framework developed at TU Delft provides a good starting point for future research to explore this mutual turbulence/coating interaction in relation to drag reduction. The papers that were produced in this line of research are expected to have an impact on the scientific community, in particular in the field of drag reduction research.
The research on thermoresponsive coatings by UNEW-SCL did not provide convincing evidence for improvement of the fouling release performance, although further work is recommended to better explore this possibility.
Finally, in research at TUE structure-property relationships for both non-fluorinated and fluorinated polymeric coatings were established for a wide variety of static and dynamic relief structures. New processes were explored for their low cost and large scale manufacturing. It is anticipated that the results from this project will generate new generations of drag reduction and anti-fouling coatings which, in the not too distant future, will have a positive impact on the protection of our marine environment.
WP2
The outcomes of the Seafront project relating to WP2 (Surface chemistry based) can have a significant potential impact on future improvement of the fouling control technologies.
The results delivered by this WP consisted in fact in one technology selected for field trials (the Tecnoflon® based coating) and at least other three exploitable results (PFPE-zwitterion conjugates, (nano)particles and ultra-lubricious coatings), which means a good probability that at least one of these technologies could be successfully developed in the future.
In addition, most of the formulations developed in WP2, though innovative for the chemical composition, under the coating application point of view are quite conventional and therefore easy to be applied with actual coating technologies.
Looking a bit more deeply into the detailed results, the technology which was selected for field trials (the fluoropolymer Tecnoflon®) could represent in case of success a disruptive innovation. In fact, never in the art a fluoropolymer has been applied as a coating matrix in the field of fouling release coatings, and in addition from the point of view of the Tecnoflon® polymer none of the actual applications is in the field of coating.
Obviously the timeframe and complexity of a four year project do not allow drawing of final conclusions on a single item, but just disclose possibilities which need to be further studied and in case of consistent and positive results developed under a practical and business perspective. This is the case of this coating prototype, which obviously needs to be further investigated in all the possible aspects of the formulation and the performance testing.
However, considering potentiality with the horizon of the actual data we can be really optimistic about this first technology of WP2.
Considering the other technologies classified as potentially exploitable results it is worth mentioning the PFPE-zwitterion conjugates which (at least for some selected structures) gave impressive preliminary performance results. Unfortunately such results arrived later than the deadline for deciding the prototypes to forward to field trials, so the available tests are only biological lab tests and biofilm release test. However these data are promising, being the performance equivalent to the Intersleek® 1100SR which is, to our knowledge, the top foul-release coating available. None of the other prototypes tested during the project reached this level of performance.
These PFPE-zwitterions will be investigated beyond the Seafront project and potentially they could become a future solution for fouling release coatings, especially in case they will show an advantage compared to the Intersleek® 1100SR. To fully understand these aspects we will need to scale-up these materials, investigate all the formulation and coating application aspects and also investigate performance in terms of consistency, durability, effectiveness in different fouling conditions and last but not least evaluate cost.
Another field of possible interest for this technology is coatings for biomedical applications, where there is the need to prevent contamination by bacteria and biomolecules. This PFPE-zwitterion technology may be effective also in this case, opening the road to important sustainable applications which aim to improve life to mankind.
Finally, nanoparticles based technology is another exploitable result, especially the last generation nanoparticles prepared by Fraunhofer IFAM having a hierarchical structure. The prototypes developed with this concept are under test, the first results seem promising, which could lead to a potential impact in new end user fields..
WP3
In light of the severe environmental impact resulting from the use of biocidal compounds in antifouling coatings and their consequently increasing legislative regulation, the developmental work performed within WP3 is highly relevant. The primary objective of this work package was to develop coatings with bioactive properties but zero release of toxic compounds into the environment – a challenging endeavour. While many of the devised strategies did not lead into viable coating solutions for a variety of reasons one system in fact did show competitive performance to the benchmarking coatings and was hence down-selected for evaluation in situ, namely the quaternary ammonium salts immobilized on silica nanoparticles and dispersed in Intersleek® 1100SR. The additional benefit of the QAS functionalization may lie in reduced biofilm formation particularly during inactive periods of the vessels. The system might also be suitable for application on fully stationary maritime structures, e.g. foundations of offshore wind turbines. Although it is not possible within the limited time frame of the Seafront project to fully assess the potential of this technology the prospects in terms of feasibility and economic viability are very good. The manufacturing process of the QAS-functionalized nanoparticles is already very mature and the combination with the commercial paint system can be realized at reasonable effort. Thus, in case of continued positive performance this technology could well mount into a commercial product leading to improved performance of fouling release coatings.
Although the other investigated technologies could not be advanced to a comparative level of commercially exploitable results they nevertheless provided new scientific knowledge and many of them will be taken forward in future R&D projects. The most relevant of these potentially exploitable results are outline below:
1. Chitosan. As a biopolymer and true byproduct of the shellfish industry this substance is highly interesting for various coating applications:
• Novel antimicrobial acidic chitosan coatings for hygienic, indoor, or medical applications
• (Partial) substitution of biocides in self-polishing antifouling coatings
• Replacement of fossil-based polymers in resins
2. Polyhydroxyalkanoates: These biodegradable biopolymers are highly interesting for eco-friendly coatings:
• (Partial) substitution of biocides in self-polishing antifouling coatings
• Replacement of fossil-based polymers in resins
3. Selektope®: Although the primary objective of non-release could not be achieved due to a resulting loss of function, this substance remains of high interest for antifouling coatings. Due to its non-lethal and very specific effect against animal fouling at very low concentrations it has a much lower environmental impact than many other biocidal compounds.
4. Polyglycerols: They proved to be very effective for reducing adhesion of proteins and microorganisms and are hence very interesting for antimicrobial coatings for short-term medical applications.
WP4
The laboratory-based evaluations of candidate coatings were fundamental to the successful selection of the three technologies chosen for field trials in WP5 and WP6. These assays were complemented by hydrodynamic testing of the Modified Intersleek® Riblets at TU Delft, highlighting the drag-reducing properties of this hybrid technology. The latter is the subject of a paper to be submitted to Biofouling.
Rather than standard statistical analysis of data, a meta-analysis approach was adopted to compare the performance of coatings in the various assays. This approach, which forms the basis of an article that will be submitted to Biofouling, has the potential for bringing about a step change in the methodology for efficacy testing of antifouling coatings.
Improvements to the flow cell at UNEW, including modifications to accommodate large panels, have provided a state-of-the-art testing device for pressure drop and fouling release measurements. With its ability to accommodate panels deployed on a research vessel, through a strut arrangement developed in WP5, the facility provides a near seamless means to measure the impact of real-world fouling on drag. This capability is unique and in addition to forthcoming journal publications, will have lasting impact as an analytical service to the wider research communities.
New algorithms were developed that allow the simultaneous, real-time tracking and classification of the settlement behaviour of multiple barnacle cyprids on surfaces over many hours. This advance is likely to have an impact on the scientific community interested in colonisation of surfaces, particularly since the wider utility of the method has been demonstrated for tubeworm and diatom species. The development of the algorithms and methodology was published in The Journal of the Royal Society Interface and future publications on applications of the technology are anticipated. Moreover, the methodology can be refined, based on the knowledge gained, as a high throughput means to evaluate to deterrent value of surfaces to fouling organisms.
Advances were also made in the molecular biology of fouling. A transcriptomic approach was adopted at UGOT to study differential gene expression from pre-settlement behaviour of barnacle cyprids through to the juvenile, with a number of candidate genes involved in surface exploration, fixation and metamorphosis identified. These studies are ongoing but the ‘pipeline’ for gene expression studies and the fundamental knowledge gained are highly relevant to exploring mechanisms of antifouling efficacy and thus identifying new targets for antifouling research. Indeed, the methodology will be applied to the three technologies down-selected in WP4. At BRIS, a metagenomics approach was used to investigate biofilm formation on commercial biocidal anti-fouling and fouling release coatings. Method development has enabled community analysis of bacteria, archaea and eukaryotes with clear differences in taxonomic abundance detected between biocidal anti-fouling and fouling release commercial coatings and indeed, between fouling release coatings. Gene level analysis also revealed some differentially abundant genes across the coating types. Although more work is needed, the approach should ultimately lead to a more complete understanding of the dynamic relationship between the different components of the biofilm community and targets for fouling control measures. The bacterial community analysis work has been submitted for publication in Biofouling and future publications on the wider community composition and differentially abundant genes are anticipated. More immediately, and given the importance of biofilm to marine vessel performance, a likely impact of the method development is the availability of a new analytical service.
WP5 & WP6
The innovative and unique development of low cost sensors for environmental monitoring may lead to the possibility of large scale deployment and crowd source based collection of environmental data on a global scale at high resolution. Implementation would be low cost due the selection of specific low cost sensors at the design stage. Customers and users of this could include fish farms, commercial fishermen, water utility companies, harbour authorities, ship routing systems, shipping companies and marine coating manufacturers.
The monitoring of environmental parameters simultaneously with the fouling control performance of coatings can be exploited by the permanent monitoring of water quality at test sites used to evaluate fouling control coatings. The developed low cost water quality sensors designed for deployment on static platforms would have the logged data uploaded into a central site using the software scripts written during the project from where it can be subsequently accessed. If combined with Earth Observation (EO) data, vessel track data captured from sources such as AIS and oceanographic models it could be used to determine the environmental conditions experienced by a ship, offshore platform, renewable ocean energy device or other marine based infrastructure (for example aquaculture nets) in real time anywhere.
The TeamSurv platform being worked on by SMAR could be expanded to support EO data and would enable the EO data to be tied in with in-situ measurements and vessel tracks and link with satellite derived bathymetry. The potential applications and uses for this would be marine environmental monitoring, data sets used for advising on best coating for a given location and integrating parameters along trading routes to model and analyse optimal schedules. Other applications include monitoring of algal blooms and their movement and enhanced monitoring in fish farming aquaculture applications.
The improvements and upgrades made to the RV Princess Royal to make it a fully instrumented research vessel (Strain gauges fitted to both propeller shafts to allow for high precision sea efficiency and manoeuvrability trials) enable it be deployed as a hydrodynamic analytical service to third parties or for it to be charted to conduct bespoke experiments. Marine coatings companies, naval architects, academic institutions and students share an interest in measurement of real world scenarios with a high level of precision to further understand the relationship and interactions between fouling, the vessel itself and the performance parameters.
In addition to using the vessel as a test instrument, the custom strut insert that has been designed, manufactured, installed and commissioned allows it be used as a panel deployment testbed. Deployment of test panels through the deck of the vessel ensures that the panels are deployed under genuine real world service conditions. The design uses panels which can be interchanged between deployment on the vessel or testing using other conditions. Coating suppliers, academic institutions and vessel owners would find value in using the vessel as a platform to deploy interchangeable panels for subsequent drag measurement using flow cell pressure drop or boundary laver velocimetry.
Should the testing of Intersleek® on the ¼ scale MIN Deep Green prototype demonstrate that is effective as a fouling control solution for ocean energy devices then it could subsequently be used on the full scale device with a 12m wing span. Reducing the drag caused by fouling is a priority as less drag corresponds to higher kite speed and therefore more power generated. As a further development the Modified Intersleek® Riblets could be applied to certain areas of the wing to further reduce drag beyond a hydraulically smooth surface.
The LCIA approach used in the project for the different end users with the technologies from the project has established the environmental impact of each scenario. Employing the same methodologies will be used to enable comparison of future iterations of the SEAFRONT technologies and other emerging solutions with the ones explored within the project and existing benchmarks. Additionally the methodologies will allow the addition of a new selection of materials and processes. New databases can be constructed or the existing ones modified to adapt them into other industrial sectors and quantify and evaluate the economic and societal impacts from an environmental impact and eco-toxicity point of view.
More testing in needed in aquaculture end use but the testing in SEAFRONT has shown the potential of the technologies examined. More testing is required for both the antifouling (fouling deterrence) and fouling release (fouling release/ease of clean) properties and on the process of coating large net areas. The testing methodologies involving various cleaning regimes and using photographic image analysis to determine performance could be employed in subsequent field trials. On economic and societal levels environmental friendly coatings would be welcomed by the aquaculture industry.
Marine growth can greatly impact the efficiency of tidal turbines so high performing and long-lasting coatings can assist in making tidal energy a commercially viable technology. The solutions developed in the project can also be employed for the ancillary items such as mooring lines and power cables. Floating wind turbines are an up-and-coming market that could use coatings from the project on the subsea spar area. Use of beneficial coatings would give the user an advantage over their competition. The target is to have coating product tailored toward the industry needs and environment which delivers more energy produced with less maintenance costs.
Other offshore renewable energy devices e.g. wave energy converters, tidal energy converters, offshore and onshore wind, solar and other energy sources would benefit of the drag reducing beneficial surfaces developed in the project and the economic and environmental scorecards.
Commercialization of technologies explored within the project is a realistic prospect with Confidentiality Agreements (CA’s) in place with several partners to continue the activities after the end of the project; similarly leveraged funding opportunities are being sought. Testing with end users using the SEAFRONT developed systems and commercial systems from IP will continue beyond the end of the project.
The activities within SEAFRONT have allowed IP to explore non-traditional market such as ocean energy power generation and aquaculture and non-conventional application routs in the form of laminate film.
WP7
Results of SEAFRONT have been disseminated throughout the project via publications, presentations and posters. Both academic as industrial partners have contributed to this, for instance by attending conferences in which they presented results of SEAFRONT in presentations and posters. Papers of the SEAFRONT project have been submitted to scientific journals and published. In the last phase of the project, the consortium had decided to spread its positive outcomes into a wider audience, mainly through various popular scientific media with a global reach. For this reason the consortium has made one summary text that was published right after the project.
Part of the positive outcomes of the project are possible areas for further exploitation. In the process of identifying these, a special exploitation strategy seminar was held at the end of 2016. In the last year of the project the total number of exploitable areas has grown to 19, most of which will be further developed by two or more partners of the consortium after the project. See also under xx for an extensive overview.
List of Websites:
www.seafront-project.eu
In summary, in the SEAFRONT project an alternative strategy for antifouling was developed, combining two concepts:
1. Combinations of multiple (novel) approaches/technologies into one coating solution rather than considering single technologies in isolation;
2. Considerable improvement of the fundamental understanding of biofouling and biocorrosion mechanisms so as to feedback and inform intelligent technology and advanced test method development.
Both concepts have been explored in this project through a process of parallel interdisciplinary studies combining, biology, genomics, biotechnology, chemistry and advanced surface characterisation techniques. This synergistic approach has ultimately resulted in the down-selection of promising technology combinations for which, after formulation and scale up, the antifouling performance was benchmarked in end-user field trials. The outcomes show outstanding research results, based on which in total 19 key exploitable areas that have been identified for further development.
By developing environmentally benign novel fouling control coatings with reduced drag, SEAFRONT has proven to significantly contribute to increase the efficiency and competitiveness of both mobile and stationary maritime structures by reducing operation and life-cycle costs. As 50% of the operational costs of a transport vessel are costs of fuel, only 5% reduction of drag, as was targeted in this project, was successfully achieved. This will already save $3 billion fuel costs and 20 million metric tons of CO2 emissions.
Extending the operational life span of fouling control coatings will save maintenance/operation costs for mobile and stationary maritime structures. Nowadays cost of ownership/operation of a container vessel includes $450,000 per scheduled repair period, which includes dry docking and other maintenance costs. Lower the frequency and time of dry docking for renewal of antifouling coatings can reduce cost of operation significantly. Bluewater expects that novel fouling control coatings will lower the maintenance costs of marine energy devices by approximately 40% since frequent cleaning at sea, lifting of the device out of the seawater to clean it (downtime) and expensive underwater inspections will become obsolete.
Furthermore, SEAFRONT has contributed to the EU Marine Strategy Directive by have established a framework for the necessary actions to be taken in order to achieve and maintain a good environmental status in the marine environment by year 2020. The Directive states that marine strategies shall be developed and implemented in order to:
a. Protect and preserve the marine environment, prevent its deterioration or, where practical, restore marine ecosystems in areas where they have been adversely affected.
b. Prevent and reduce inputs in the marine environment with a view to phasing out pollution as defined in Article 3(8) of the Directive, so as to ensure that there is no significant impact on or risks to marine biodiversity, marine ecosystems, human health or legitimate uses of the sea.
Project Context and Objectives:
The SEAFRONT project’s aim was to significantly advance the control of biofouling and reduce hydrodynamic drag by integrating multiple technology concepts such as surface structure, surface chemistry and bio-active/bio-based fouling control methodologies into one environmentally benign and drag-reducing solution for mobile and stationary maritime applications. In parallel, a combination of laboratory-based performance benchmarking and end-user field trials has been undertaken in order to develop an enhanced fundamental/mechanistic understanding of the coating-biofouling interaction, the impact of this on hydrodynamic drag and to inform technology development and down-selection of promising fouling control solutions. This project’s aim was to facilitate a leap forward in reducing greenhouse gas emissions from marine transport and the conservation of the marine ecosystem by adopting a multidisciplinary and synergistic approach to fouling control.
The overall objectives of the SEAFRONT project were:
1. Cost-effective coatings solutions with reduced environmental footprint as determined by comparative life cycle and eco-efficiency assessment
2. 50% improvement in biofouling deterrence (% coverage) and/or biofouling release (% release at a given speed over time) as compared to latest state of the art commercial reference controls.
3. Hydrodynamic drag reduction resulting in a consequent 5% improvement in operating efficiency as compared to that offered by Intersleek® 900.
In parallel, as an integral ethos within the project, a strong fundamental/mechanistic understanding and new performance predictive test methods have been developed to feedback and inform technology evolution and down-select promising coating solutions for end-user field trials.
In WP1 we have explored the technology concept of surface structure-based biofouling control strategies. This concerns strategies of which the working principle is based on surface properties of antifouling coatings such as the surface texture, the surface energy and the surface wettability. We have worked on two different technology vectors within this concept, namely textured coatings – drag reduction coupled with an antifouling effect – and switchable coatings – antifouling coatings which respond to stimuli.
WP2 was centered around the development of materials and materials combinations which prevent biofouling based on a fouling release mechanism. The highest performance commercial fouling release coatings currently utilise fluoropolymers (Intersleek® 900). To deliver the step change in performance required of a next generation technology, a combination of the unique properties of a fluorinated system with a secondary effect was needed to deliver total fouling deterrence and release. Within this work package three main classes of materials have been developed and formulated into coatings with improved performance compared with the state-of-the-art, namely innovative zwitterionic materials with a fluoropolymer anchors, fluoro-functionalized particles used as fillers or bulking agents, and domain-structured materials based on a combination of fluoropolymers with hydrogenated polymers.
Coating formulations have been prepared from first generation polymers and particles, both of which have been developed and optimized upon feed-back of their performance evaluation which has been assessed in WP4 and subsequently has led to iterative preparation of polymers, particles and coating formulations with a progressive enhancement in overall performance.
WP3 was dedicated to the development of fouling control coatings utilizing generally non-toxic, environmentally benign bioactive compounds. Where active substances are employed, WP3 was clearly focused on minimizing the environmental impact of these substances by developing non-release strategies. Given that the market for antifouling coatings is however currently dominated by releasable biocidal technologies some comparative investigation of controlled release has been performed in order properly benchmark antifouling efficacy.
WP4 has delivered high-throughput, iterative evaluation (biological/chemical/physical, including hydrodynamics) of surfaces/coatings for physico-chemical and hydrodynamic characteristics, and antifouling/fouling release efficacy in lab-scale tests. This has served to down select surfaces/coatings for field testing and provided a preliminary assessment of mechanism of action. More in-depth analysis has been done on selected surfaces/coatings as well as model surfaces prepared for hypothesis-driven experiments to improve our mechanistic understanding of biofouling and its control. In addition to the wide-ranging biological, surface analytical and hydrodynamic testing methodology established in WP4, new testing methods have been developed and molecular biology techniques, including next generation DNA sequencing, have been utilised to provide beyond state-of-the-art mechanistic understanding of biofouling and biocorrosion.
WP5 has served to evaluate the performance of solutions developed within the technology work packages (WP1-WP3) and which have been down selected based on anti-fouling, anticorrosion and hydrodynamic performance within WP4, in their intended working environment via:
• Creation of a set of defined product and application requirements for each end-use(r)
• Formulation of the technologies
• Deployment of down selected technologies and evaluation of the performance
• Evaluation of the environmental and economic footprint of technology scale-up, implementation into service and through life impact of in-field demonstrated technologies
• Scaled up manufacture of the successful technologies to volumes suitable to conduct full scale end-user trials.
• Full scale trails for end-user markets (shipping, off-shore, renewable energy, aquaculture).
In WP6 the scalability and fitness for purpose was demonstrated on an industrially and commercially viable level of the prototype technologies developed within WP1-3, down selected in WP4 and shown to have in-service and in-situ performance within WP5. This has been delivered by means of cost effective scale-up of production to industrially relevant volumes and application of this scaled up material to commercial infrastructure operated by the relevant end-users.
WP7’s prime objectives were dissemination, standardisation and exploitation of project results.
WP8 deals with the management of the EU work according to the rules and regulations laid down in the Grant Agreement closed between the EC and the consortium and the coordination of work with SEAFRONT. The project management concerns the coordination, administration, financials, contracts and intellectual property management of the project.
Project Results:
WP1 (Surface structure based biofouling control technologies)
The approach of WP1 was based on the “surface structure” of coatings, which concerns antifouling strategies where the working principle is based on the surface properties of coatings such as the coating texture, elastic moduli, surface energy and wettability. The aim was to develop environmentally benign coatings that are both effective in biofouling control and in reducing the hydrodynamic drag. Three different routes where explored. In the first route coatings were developed with a so-called shark-skin riblet structure for drag reduction and a fouling release formulation for biofouling control. In parallel detailed computer simulations were performed to study the hydrodynamic behavior of a new type of riblet structure, the so-called herringbone riblet, which is inspired by the surface texture of bird feathers. In the second route a theoretical/numerical study was devoted to the interaction between a turbulent boundary-layer flow and a compliant (viscoelastic) coating. In the third route switchable coatings where developed that can change their surface wettability and texture in response to a change in water temperature and shear stress, respectively. The idea is to use this principle for biofouling control by preventing settlement and/or enhance fouling release performance. Below the main results of the different routes will be highlighted.
Development of riblet coatings with fouling release formulation
The first months of the project were dedicated to investigations how the riblet embossing technology of Fraunhofer IFAM needs to be adapted in order to be compatible with the elastomeric fouling release coating system Intersleek® 1100SR. Samples of the standard formulation of Intersleek® 1100SR could not be used directly with Fraunhofer IFAM’s riblet producing procedure. Interaction between the resin, the solvent and the mould caused poor sample removal resulting in unacceptable pattern fidelity. Two alternative nearly solvent free formulations were developed one with only the solvent removed (causing a viscosity increase) and the second with solvent removed and adjustment of the thixotrope package so as to maintain the viscosity comparable with that of the standard paint. Both examples are thermoset coatings where crosslinking is brought about by catalyst initiated condensation cure. Only the embossing trials with the first solvent free formulations appeared to be successful, resulting in a generally good riblet quality with sharp ridges.
With this modified methodology several prototype samples (referred to as Modified Intersleek® Riblets) have been prepared for hydrodynamic and antifouling testing in WP4: coated Taylor-Couette cylinders and flat Plexiglass plates were send to TU Delft for hydrodynamic testing, and microscope slides and PVC samples were send to, respectively, UNEW-MST for barnacle and diatom screening assays, and slime farm + field testing by IP. The results from the hydrodynamic and antifouling testing are very promising, showing indeed similar drag reducing performance of the Modified Intersleek® Riblets as for the standard (non-antifouling) Dual-cure Riblets of Fraunhofer IFAM, while (after exposure to flow) the antifouling tests showed similar performance compared to the smooth (non-textured) Intersleek® 1100SR. A paper has recently been written on the results and is expected to be submitted soon to Biofouling, one of the leading scientific journals on biofouling research.
The development of the Modified Intersleek® Riblets is one of the key exploitable results of the Seafront programme and has a promising potential for use on moving vessels. Furthermore, the Modified Intersleek® Riblets are 1 out of the 3 coatings that have been chosen for down-selection and further field testing in WP5.
Numerical studies of the hydrodynamic behaviour of (herringbone) riblets and compliant (viscoelastic) coatings
TU Delft performed fully resolved numerical simulations (DNS) for flow over (possibly) drag-reducing surface textures, namely textures with riblets arranged in either a parallel or a herringbone pattern. Our simulations suggest that the herringbone texture is not drag-reducing.
Further research focused on the use of compliant coatings for turbulent drag reduction. The deformation of a compliant coating in a turbulent flow was determined from an analytical model, which showed reasonable agreement with experiments performed at TU Delft in another PhD project. The model can be used to estimate for which flow and coating parameters the coating deformation is so large that an interaction with the flow can be expected. However, the model does not capture the interaction itself, so it cannot predict whether the interaction will yield a drag reduction or increase. Future investigations should address this interaction when assessing the use of compliant coatings for drag reduction.
The results of the riblet study have been published in Journal of Turbulence and we will submit soon (February 2018) another paper to Journal of Fluid Mechanics on the deformation of a compliant, viscoelastic, coating under a turbulent flow.
Development of thermo and stress-responsive coatings
This line of research was conducted by 2 different groups in separate subprograms.
Research at UNEW-SCL
Thermoresponsive, tunable LCST (lower critical solution temperature) hydrogel materials based on oligoethylene glycol methacrylate methyl ethers have been shown to be highly resistant to marine biofouling (B. Amphitrite barnacle cyprids, N. perminuta diatoms and marine bacterial/diatomaceous ‘slime’). These promising results suggest further investigation of such materials to be of significant interest. Polymer brushes based on analogous monomers performed less well than the hydrogels and were significantly more challenging to produce. Physiochemical characterization of these materials has shown them to be highly solvated with well-defined thermoresponsive behaviors and measurement of the surface properties has allowed correlation with anti-biofouling performance. Apparatus has been developed to allow measurement of the fouling release properties of these coatings to be established under flow conditions upon transition through the coating LCST.
We prepared a series of coatings based upon poly(oligoethylene glycol methacrylates) which display near-identical chemical functionality but differ in their cloud point temperatures. All of these coatings did not undergo significant settlement with barnacle cyprids or diatoms below their cloud points (i.e. even before they were switched), making it hard to evaluate if the thermoresponsive nature of the coating actually would have any benefit. This result does, however, indicate the encouraging performance of poly(oligoethylene glycol methacrylate)-based coatings. To better test the performance of our polymer coatings as their temperatures were modulated under flow conditions, we constructed a heating platform for use with the Newcastle flow cell. Samples were fouled with diatoms and placed upon the heating platform, however a preliminary experiment indicated that no improvements to their fouling release properties were observed under flow. It is possible that further experiments exploring more extended heating/cooling cycles might reveal an improvement, but the complexity of these experiments coupled with instrumental problems meant no further work could be completed. In summary, no convincing evidence could be found to suggest thermoresponsive polymer coatings present benefit in fouling release studies, although further work would be recommend to better explore the possibility.
Research at TUE
A wide variety of micro-structuring techniques were explored in combination with both non-fluorinated and fluorinated polymeric coatings with an emphasis on anti-fouling and drag reduction. Coatings with a dynamic surface relief structure were explored and it was shown that complex relief structures can be produced which switch to a flat state in response to external triggers such as temperature and PH.
Fluorinated coatings based on crosslinked and/or thermoplastic polymers were also investigated and it was shown that micro-structures suitable for anti-fouling and drag reduction or combinations thereof can be produced. The micro-structuring can be performed with processes that use (i) mask exposures and UV-light and (ii) processes employing thermal embossing/imprinting. In all cases, it was found that on-reactive fluorinated species (so-called lubricating oils) are required to generate anti-fouling levels which are comparable to the bestcommercial alternatives. A range of micro-structures can be obtained with the appropriate dimensions and accuracy for both anti-fouling and drag reduction.
A substantial effort was devoted to identifying materials and processes that can be used on a large scale at a low cost. It is argued that rubber-like thermoplastic (co-)polymers with specific lubricating oils processed via imprinting/embossing are an excellent alternative to the currently used crosslinked systems especially if further optimization occurs with respect to adhesion to substrates and anti-fouling.
In conclusion, structure-property relationships were established for a wide variety of static and dynamic relief structures and new processes were explored for their low cost and large scale manufacturing. We anticipate that the above-described results generate new generations of drag reduction and anti-fouling coatings which, in the not too distant future, will have a positive impact on the protection of our marine environment.
WP2 (Surface chemistry based biofouling control technologies)
The approach of WP2 was based on the “chemistry of the surface”, aiming at developing new solutions to get fouling release coatings hopefully more effective than the benchmark, identified as the commercial coating Intersleek® 900. This means modification of the surface by application of a coating layer (in principle smooth) which has an innovative chemical composition acting effectively in a fouling release type manner.
The initial program of this WP was made of several tasks, which represent different routes, each one involving a specific chemistry to build-up the active ingredient of the final coating formulation.
The know-how relating to fouling release coatings before this project suggested to explore three main promising technologies, which can be identified as: i) zwitterionic materials; ii) innovative (nano)particles; iii) ultra-lubricious surfaces.
Zwitterionic materials
A zwitterion is a molecule having at least two functional groups, one positively charged and the other negatively charged, being the overall charge of the molecule zero. Zwitterions have been included in this project because in the literature some zwitterions are reported to have a significant anti-fouling behavior.
We attempted two approaches following this route, the first one employing only hydrogenated zwitterions, the second one which tried to combine the zwitterion with a fluoropolymer (more specifically a perfluoropolyether (PFPE) ) in order to keep physically grafted the zwitterion to the coating surface and hopefully resulting in a synergistic performance effect.
The first approach was pursued by UNEW-SCL, which used a specific technique to chemically graft on a glass surface commercial zwitterionic monomers (carboxybetaine and sulfobetaine methacrylates) or mixtures of positively or negatively charged monomers. After grafting different combinations of these monomers, this modified surface was evaluated (by UNEW-MST in WP4) using two biological tests on the lab scale (the diatom settlement assay and the barnacle cyprid settlement assay). Preliminary results of the biological assays showed very similar anti-fouling properties for the coatings independently from their content of zwitterionic monomers. These results were confirmed by additional tests, which concluded that the incorporation of the carboxybetaine methacrylate into the hydrophobic coating does provide only a minor enhancement of the anti-fouling properties, whereas the sulphobetaine does not provide any significant effect. Better results were obtained with the negatively or positively charged monomers: coatings having an excess of charge showed an improved performance in the biological assays.
However the relatively scarce performance combined with the difficulty to scale up this grafting methodology in the end did not justify any scale-up or field trials of this route.
The second approach relating to the PFPE-zwitterionic conjugates was developed by SOLVAY and UNEW-SCL for the synthetic part and by IP for the formulations. Several prototypes were prepared using different functionalization approaches, the most of them containing zwitterionic groups chemically linked to the chain ends of a PFPE molecule. Overall, 29 PFPE-zwitterionic conjugates were delivered to IP, which tried to incorporate such materials into coating formulations (one based on PDMS and the other one on a polyacrylic resin). In the end they succeeded to formulate 12 prototypes (of the 29) at 10% loading in the resin matrices.
The biological tests revealed that these coatings have a moderate performance, except two of them which showed very promising results when formulated in the PDMS resin. In particular fouling release performance (tested by a biofilm release test) resulted comparable to the commercial Intersleek® 1100SR, thus outperforming the Intersleek® 900 considered our benchmark.
Unfortunately these last results arrived lately, after the decision of which prototypes to be scaled-up for field trials had been made (EB meeting in Coimbra, February 2, 2017, during the sixth Progress Meeting of the Seafront Project). Therefore these zwitterionic prototypes were not tested on field trials within the project, however in the end they were classified as one of the key exploitable results and one of the promising outputs of the project.
Fluoro-functionalized particles
The basic idea of this second technological approach was to add suitable (nano)particles to standard coating matrices in order to improve the performance of the coatings in terms of fouling release properties.
The first approach consisted in the addition of hydrophobic and hydrophilic silica (nano)particles: such particles should deliver improved mechanical properties to the coating (e. g. PDMS), but, being functionalized on the surface, they should deliver also improved fouling release properties.
The synthesis of the hydrophobic (nano)particles was a collaboration between SOLVAY and Fraunhofer IFAM: SOLVAY synthesized several different PFPEs bearing one or more reactive silane functional groups, which were used by Frauhofer to incorporate the very hydrophobic PFPE chain on the surface of the silica (nano)particles. On the other hand Fraunhofer IFAM used a similar technique to prepare PEGylated (nano)particles, i. e. hydrophilic silica (nano)particles having on their surface PolyEthyleneGlycol chains.
The preparation of the (nano)particles was successful: Fraunhofer IFAM demonstrated to have chemically linked the PFPE or the PEG chain onto the surface of the particles and measured an average size of about 100 nm or less. However, when IP tried to formulate these particles in the two resins mentioned above (PDMS and polyacrylic), they faces serious dispersibility problems. In fact, even using High Shear Dispersion techniques they observed a high degree of agglomeration of the particles which produced a high level of roughness to the surface of the cured films. Contact angle measurements revealed a hydrophobic behavior for all coatings, even those containing the PEGylated particles, which is probably due to the bad dispersion of the particles.
During the last year of the project Fraunhofer IFAM tried to follow a slightly different approach consisting in adding to the silica (nano)particles other larger PTFE particles in order to achieve a hierarchical structure of particles in the coating matrix. This approach seemed to improve dispersion of the particles in the PDMS matrix and tunable surface effects were observed. Immersion tests on these prototypes started in July 2017 at the Fraunhofer IFAM site for static immersion tests, where nylon nets were also treated with some of these prototypes. Results after six months seem promising, but more time is needed to give a final assessment.
In summary this route was not selected for field trials, but it is considered among the possible exploitable results of the project.
The second approach with (nano)particles was based on fluoropolymer latexes, i.e. water based dispersions containing stabilized fluoroelastomeric (nano)particles. These latexes originate from the microemulsion polymerization, a proprietary SOLVAY technology used to synthesize fluoroelastomeric polymers. These latexes were taken in consideration with the idea to develop water based coatings. Blends have been prepared by IP with water-borne polyurethanes and acrylics. The most promising results have been given by polyurethanes: surface analysis showed some indications that surface enrichment was taking place. However the activity on this class of water based coatings was limited and final conclusions are not possible. These results could be the base for future developments when sustainability of the solvent based formulations will be seriously endangered.
Domain-structured materials creating ultra lubricious surfaces
This last route is based on the modification of the coatings with fluoropolymers, which could deliver outstanding fouling release properties. This attribute of fluoro-modified polymers is well known in the art, even though only some chemical architectures and compositions are effective and no rules are available how to select such formulations. Being fluoropolymers very incompatible with hydrogenated resins, the morphology of the coating at the nano-scale will be presumably domain-structured and hopefully should create a ultra-lubricious effect.
Two approaches were followed: a first one consisted in chemically linking the fluoropolymer to the hydrogenated resin, whereas the second one is a physical dispersion of the fluoropolymer.
According to the first approach, several PFPE bifunctional derivatives were prepared by SOLVAY and delivered to Fraunhofer IFAM and IP. The functional groups of these derivatives were: hydroxy, amine, epoxy. Fraunhofer IFAM made many formulations introducing in small amounts (low relative weight percentage) the functionalized PFPEs into different polymers like polyurethanes, polyesters and epoxy. Of the 49 coating systems prepared, eight were selected for the biological tests, which gave moderately positive results for only one formulation. IP tried to use mainly the PFPE diol in polyurethane polymer compositions, but did not succeed to obtain good performance results.
Based on these poor outcomes this technology was not selected for field trials.
Instead, much more promising results were obtained with the second approach, using a fluoropolymer by SOLVAY commercially known as Tecnoflon®. This material is a co-polymer of fluorinated and partially fluorinated olefins, which becomes after cross-linking a fluoroleastomeric rubber (FKM) with very high chemical and heat resistance, which is used in demanding applications that cannot be reached by the hydrogenated rubbers.
The polymer prior cross-linking is a solid plastomeric material, with glass transition temperature well below room temperature and slight solubility in polar organic solvents, such as ketones. Several grades of this material have been provided to IP, which tried initially to use them as physical additives in hydrogenated resin formulations. However, they soon discovered that the neat material can easily give a coherent film, and therefore they started to evaluate this polymer as a matrix in substitution of the PDMS. With this perspective they selected some formulations containing suitable PFPE derivatives, which gave very promising results in the biological assays.
Therefore this Tecnoflon® based technology was selected as one of the prototypes to scale-up for field trials.
Panels were prepared and assembled on the Royal Princess for evaluation during summer/fall 2017. Data acquisition is still ongoing.
WP3 (Bio-based and bio-active biofouling control technologies)
WP3 was dedicated to the development of fouling control coatings utilizing generally non-toxic, environmentally benign bioactive compounds. Where active substances were employed, WP3 was clearly focused on minimizing the environmental impact of these substances by developing non-release strategies. Given that the market for antifouling coatings is however currently dominated by releasable biocidal technologies some comparative investigation of controlled release has been performed in order properly benchmark antifouling efficacy.
Three different bioactive compounds were selected for investigation in Seafront:
Selektope®, an organic, non-metal compound belonging to the group of imidazoles that induces the swimming reflex of barnacle larvae and thus prevents their settlement;
Quaternary ammoniums salts (QAS) immobilized onto silica-based nanoparticles;
Chitosan, a natural biopolymer obtained by deacetylation of naturally occurring chitin.
Selektope® interferes with the normal behaviour of cyprid larvae during surface exploration prior to settlement. When larvae arrive and attempt to explore a surface, Selektope® stimulates a response which induces a deterrence effect and results in the organism swimming away from the surface. Due to its specific and non-lethal mode of action, efficacy can be achieved by incorporation of low amounts of Selektope® relative to the biocide content in traditional antifouling coatings.
Quaternary ammoniums are well known antimicrobial agents, specific compounds of which are currently under BPD evaluation for non-marine end-uses. The likely mechanism of action involves ion exchange between the positive charges on the surface and structurally critical mobile cations within the membrane. The loss of these structural cations results in a fatal loss of membrane integrity in the microorganisms.
Chitosans are polyaminosaccharides obtained by deacetylation of naturally occurring chitin. Chitosans show a broad spectrum of antimicrobial activity, which has been explained by (i) cell wall leakage by ionic surface interaction or by teichoic acid binding and extraction of membrane lipids, (ii) mRNA and protein synthesis inhibition and (iii) suppression of microbial growth through external barrier formation and metal chelation. Unlike other natural bioactives chitosan is available economically and in large quantities due to it being a by-product of the shellfish industry. Furthermore, it is rapidly reintegrated into the marine environment through natural decomposition pathways and therefore environmentally benign.
Additionally, a fourth group of compounds has been considered for surface functionalization in WP3, namely polyglycerols. Dendritic and linear polyglycerols are able to dramatically reduce the non-specific interaction of proteins with surfaces. Among the various polymeric architectures, dendritic ("treelike") and linear polyglycerol polymers have experienced an exponential development due to their multifunctional and well-defined structures. These polymers exhibit good chemical stability and inertness under biological conditions and are highly biocompatible.
For the above mentioned bioactive compounds, an environmental risk assessment was carried out. All three bioactives exhibit acceptable risk ratios in the marine environment with the exception of QAS in the sediment compartment. However, a refinement of the risk assessment based on a complete data set with regard to the required tests would likely lead to an acceptable risk profile also for QAS.
Different strategies to immobilize the active compounds on the coating surfaces have been investigated so as to create antifouling coatings that do not release any bioactive compounds into the environment. Samples have been produced with immobilized polyglycerols, QAS, Selektope®, and chitosan. These samples were characterized with regard to their surface properties and laboratory settlement assays at Newcastle University were performed for the non-toxic samples and field immersion tests for some other samples. One of the immobilization strategies focused on tethering the bioactives to a phosphate fluorofluid for subsequent incorporation into a fluoropolymeric paint matrix. The samples containing QAS fluid showed very good early slime resistance, but performance diminished rapidly presumably due to the fluid leaching out of the film. Samples with Selektope® fluid showed lower antifouling performance as compared to Intersleek® 1100SR. A general challenge in working with chitosan is the poor solubility in organic solvents and hence it was not possible to generate compatibility with this kind of approach.
The second approach to realize permanent immobilization of the active compounds to the coating surfaces was based on covalent coupling reactions. It comprised the use of QAS immobilized onto silica nanoparticles, a patented technology already commercially available for a series of other applications (http://www.matera.pt/technology/ambio/). These functionalized nanoparticles were dispersed in Intersleek® 1100SR. Samples with this experimental nanocomposite coating yielded promising results in the various biological tests, i.e. antimicrobial activity against selected bacteria strains, settlement assays with diatoms and barnacle cyprids (WP4) as well as preliminary field immersion tests. Therefore, this coating system was down-selected for benchmarking and performance evaluation in situ within WP5. Immobilized polyglycerols showed good performance in bacteria and algae tests but their stability was insufficient under seawater conditions and the effect was lost after several weeks. Selektope® is a small molecule and hence represented a specific challenge regarding covalent coupling without blocking the active site responsible for inducing the reaction in the cyprid larvae. The results from the barnacle assays suggested that the immobilization had not been successful and that Selektope® leached out of the coating sample. Lastly, immobilization of chitosan invariably led to the loss of the antimicrobial activity under neutral or slightly basic seawater conditions. Therefore, different attempts were made with modification of chitosan in order to maintain the antimicrobial properties also under non-acidic conditions. The use of water-based acidic binder systems in combination with specific aqueous acid solutions for dissolution of the chitosan yielded promising results. Since such systems are only of limited water stability they will be useful for other applications rather than antifouling coatings.
The third objective in WP3 was to develop and investigate a new generation of self-polishing coatings based on bioactive and biodegradable polymers. The underlying objective of all current self-polishing coatings is the controlled release of a toxic biocide. Within SEAFRONT, the aim was to abandon the use of toxic biocides completely and rely instead on the self-polishing effect of the biopolymers supported by the antimicrobial activity and hydrophilic character of chitosan, hydrophilicity being known to be an important parameter in inhibiting protein adhesion. The ultimate goal was the development of a coating based on a maximum content of natural biodegradable material in order to achieve the optimum benefit in terms of eco-efficiency and sustainability. Two groups of bio-based polymers were selected for this purpose: polyhydroxyalkanoates (PHA) and chitosan. Initial work focused on identifying suitable organic solvents for the two substances. This proved difficult for both substances. Albeit repeated trials also with lower molecular weights and finer particle sizes the problem could not be overcome and both compounds will most likely have to be chemically modified in order to make them suitable as polymeric binders. Therefore, an alternative approach has been investigated to use PHA and chitosan as additives in self-polishing antifouling paints. Several different formulations have been developed either i) replacing ZnO by PHA or chitosan, ii) replacing total pigments in the paint resulting in 5% PHA or chitosan in the finished paint, or each 2.5%. Initial results showed some potential synergy in using a combination of PHA and chitosan in an antifouling formulation but with longer immersion this effect seems to be decreasing. A non-toxic paint containing PHA has been tested for slime settlement and clearly outperformed all biocidal coatings over a period of over 50 days. Non-toxic chitosan and PHB containing coatings immersed in Singapore exhibited very poor performance against animal fouling. Recent work has focused on modification of PHA so as to achieve smaller molecules with better solubility behaviour and an aqueous PHA dispersion was successfully developed from which clear stable coating films could be produced.
The last objective of WP3 was to demonstrate that immobilization of a bioactive has no adverse effect on its antifouling performance. To this aim comparative studies were carried out with the bioactives being physically dispersed in a coating matrix. Results with the QAS nanoparticles indicate that the antimicrobial performance of the self-polishing coatings is inferior to the Intersleek® 1100 SR and PDMS systems functionalized with QAS nanoparticles. For Selektope® on the other hand, the inclusion into an SPC binder showed an improved antifouling performance particularly for the Selektope® fluorofluid. This corroborates the conclusion from the immobilization studies that Selektope® cannot be tethered to the coating without losing its effect.
In conclusion, the development of more eco-friendly-based antifouling coatings represented a series of challenges which could not be fully overcome within SEAFRONT. Nevertheless, very promising approaches could be identified which might be further pursued in the future.
WP4 (Characterisation, Fundamental Understanding & Performance Prediction)
The main aim of WP4 was to deliver high-throughput iterative evaluation of surfaces so that down-selection could be made for field testing. Additionally, the WP aimed to develop new testing methodologies and through fundamental studies, improve our understanding of marine biofouling and corrosion. WP4 comprised five subsections: 4.1 physical/chemical characterisation; 4.2 hydrodynamic characterisation; 4.3 biological evaluation; 4.4 test method development/refinement; and 4.5 fundamental understanding of biofouling and corrosion.
Physical/chemical characterisation
Most of the work on physico-chemical characterisation was done, as originally proposed, by partners producing surfaces in WPs 1-3. WP4 focussed on characterisation of the coatings down-selected from WPs 1-3. At UNEW, six reference coating samples: Intersleek® 700, Intersleek® 900, Intersleek® 1100SR), Intersmooth® 7460HS, Intersmooth® 7465Si and Intercept® 8000 LPP were studied, as well as surfaces developed by UNEW – a thermo-responsive polymer (polymer brush of polyethylene glycol methyl ether methacrylate (PDEGMA)) and zwitterionic surfaces. This study used atomic force microscopy (AFM) to investigate many surface properties including morphology, roughness, Young’s modulus, adhesion strength, stiffness and nanoindentation. The static contact angle of the wet coatings under water was determined by the captive bubble technique. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to study the chemical composition of the control and new coating films.
Hydrodynamic characterisation and development of new hydrodynamic testing methods
Frictional drag measurements on surfaces were made using using the Taylor-Couette (T-C) facility at TUDP and the flow cell (modified under D4.4) at UNEW. The T-C setup proved a useful tool for quick assessment of differences in the skin friction of coatings at high shear Reynolds numbers as compared to standard drag plate measurements in a water tunnel. For accurate and reproducible skin friction measurements it was essential to: (1) soak newly provided coatings in water for at least 24 hours; (2) ensure sufficient adhesion of a coating foil on the T-C cylinder; and (3) ensure sufficient sharpness of the riblet tips in case of riblet coatings. A highlight of this work was the demonstration that the modified Intersleek® fouling release coating with riblet texture, developed within WP1, exhibits the same drag-reducing performance as the standard polyurethane riblet coatings of Fraunhofer IFAM. The optimum drag reduction was about 6%.
The flow cell at UNEW was modified such that the turbulent flow experienced over the surface of a ships’ hull could be replicated. For conciseness, modifications and method analysis done in WPs 4.2 and 4.4. will be combined here.
The flow cell was improved by replacing the measuring section with a new testing section. The old test section accommodated 76 mmm x 26 mm microscope slides. While this capability was retained, the new test section, made from stainless steel, was designed to accommodate UNEW standard flat test panels measuring 600 mm x 218 mm x 15 mm. This meant that skin friction measurements could be made on coated panels that had been exposed on the strut system of the RV Princess Royal in WP5. CFD simulations were carried out for the modifications to the flow cell. These included a new contraction section with a more favourable side profile, a lengthening of the test section from 2500 mm to 2700 mm and new pressure taps along the side walls of the pressure drop section for frictional drag measurements. The CFD simulations predicted that the turbulent flow would be fully developed in the new pressure drop section. Wall shear stress measurements and the shape of the velocity profiles confirmed this. Furthermore, with a channel height of 10 mm and an inlet flow speed of 0.5 m/s, shear stresses of approx. 250 Pa were predicted, corresponding to full shear stress on hull forms in excess of 30 knots full-scale speeds. Once the modifications were completed, the pressure drop methodology was evaluated against direct boundary layer measurements using three duplicate test surfaces: hydrodynamically smooth acrylic; a fouling release coated panel; and a self-polishing copolymer-coated panel. Roughness measurements were made with Uniscan’s OSP100 laser profilometer. Boundary layer profiles were obtained using the Emerson Cavitation Tunnel (ECT) and DANTEC’s two-component fibre-optic Laser Doppler Anemometer (LDA). These were compared with the skin friction measurements obtained by the pressure drop method. Although the methods cannot be compared directly, good correlations were obtained for the reference surfaces in terms of friction velocity and skin friction coefficients up to the maximum velocity of the Emerson Cavitation Tunnel (ECT) of 6 m/s.
A comparison of the hydrodynamic performance of biofilmed (developed under dynamic conditions on the RV Princess Royal for approx. 6 months) vs. clean fouling release coatings (IntersleekS 700, 900 and 1100SR) in the form of plots of wall shear stress vs Reynolds number (Re) revealed little difference between the two conditions. The exception was IS 900 at the highest Re values (>60,000), which gave slightly lower shear stress values in the biofilmed condition. The similarity of performance in the fouled and clean conditions likely reflects an absence of clear differences in the roughness values.
While the hydrodynamic performance of clean and biofilmed commercial fouling release coatings has been completed, a combination of a move of the ECT (including shipping to Poland for renovation) from the main campus at UNEW to a new facility at Blyth Northumberland and a late decision on down-selection of prototype coatings from WPs 1-3, has meant that the hydrodynamic performance of the latter coatings has yet to be completed. Panels coated with the three selected coatings (see below) were delivered too late in the 2017 season for field exposures to acquire biofilm and will now be exposed in early spring 2018, with the hydrodynamic measurements completed in summer 2018.
Biological evaluation
Most of the biological assays for the programme were laboratory-based and performed by UNEW but some in-house assays (e.g. mussel and bacteria) were done by partners formulating the coatings. In addition, natural biofilm ease of removal data were provided by IP using their ‘slime farm’ biofilm culturing reactor and UNEW’s flow cell. IP also provided raft settlement panel data collected in Changi, Singapore, Hartlepool, UK and Bratton, Sweden.
UNEW assayed 105 coatings (including 15 control/standard surfaces) for effects on barnacle, Balanus amphitrite, cyprid settlement and initial attachment and ease of removal of the diatom Navicula incerta. Before the laboratory antifouling and fouling release assays were performed, leachates of coatings were tested for toxicity with barnacle nauplii. Any residual toxicity (e.g. from uncured components) was removed sufficient to permit barnacle settlement assays by leaching for periods of 1-7 weeks. However, Selektope®-based surfaces completely inhibited barnacle settlement and leachates from some of the Technoflon fluoro-elastomer surfaces inhibited barnacle settlement after extended leaching periods. Nevertheless, these surfaces could be assayed with Navicula.
In order to down select coatings for further testing in WP5, a means of comparing the efficacy of coatings was needed that took account of the different surfaces and different batches of organisms used on different dates. This was achieved with reference to a standard surface that had been included in all assays, namely, PDMS. The data were converted to standardized effect size measures using the ‘Hedges g’ estimator. A different standardization was used for the data supplied by IP: the performance of each test surface was divided by the performance of the standard (PDMS) tested at the same time. Coatings were then ranked based on their relative performance in up to eight of the measures, with each measure normalized on a scale of 1-100 and a median rank calculated across the measures to give an overall ranking of performance. Based on these rankings and readiness for field performance testing, three candidates, one from each of the WPs 1-3, were selected by the SEAFRONT Executive Board: WP1 - Modified Intersleek® with riblet structure; WP2 - Tecnoflon® perfluoroelastomers; and WP3 - QAS nanoparticles.
2- and 3-dimensional tracking studies
UNEW refined the existing 2-D set up for video tracking of cyprid settlement behaviour and developed a new 3-D system. The new developments in the 2-D system comprised bespoke algorithms to reliably track cyprids and automatically characterise (using two neural network classifiers) their behaviour based on body movements. For the first time, multiple cyprids have been tracked, simultaneously, over long periods (24 hrs), encompassing their entire settlement behavioural repertoire. Moreover, the original classification of settlement behaviours into wide search, close search and inspection has been confirmed with inspection events proving a reliable predictor of propensity to settle. Based on this advance in understanding, a rapid (one hour) assay has been developed to allow high-throughput evaluation of coatings. A new tracking system, using two cameras, has also been developed to calculate the position of cyprids in three dimensions (x,y and z). A user interface has been built to allow users to calibrate the two cameras. The calibration procedure produces a 3x2 matrix that defines the 3-D dimensions of the animals during their movements. Multiple cyprids can be tracked and their trajectories estimated with this system. As the interaction of organisms with surfaces was the primary consideration of this project, most use was made of the 2-D tracking and classification system. Its wider utility has been demonstrated with trials using tubeworm (Ficopomatus enigmaticus) larvae and diatoms (Navicula incerta).
Molecular biology of barnacle settlement
UGOT established a procedure for ‘capturing’ individual Balanus improvisus cyprids, from many parallel experiments, at different stages of the settlement process: i) free swimming; ii) close searching; iii) early attached; and iv) newly metamorphosed juvenile barnacles. Twenty cyprids provided sufficient RNA to generate high quality RNA-seq data. These data were evaluated to remove various types of bias, including technical bias during sample handling and sequencing and variability in gene expression linked to different batches of cyprids. This ‘pipeline’ for gene expression studies is now being applied to the down-selected surfaces from the programme in an attempt to understand the molecular basis of antifouling.
A transcriptomic approach was taken to analyse changes in gene expression during pre-settlement behaviour, attachment and metamorphosis of cyprids. Comparison of global gene expression across settlement showed that pre-settlement stages (free swimming and close search) had similar expression patterns. However, large-scale changes occurred during the transition from a pelagic to an attached cyprid and from attachment to juvenile, i.e. pre- and post-metamorphosis. Genes upregulated during pre-settlement stages included those with functions related to transferase and DNA polymerase activity, perhaps indicative of highly active cell division, juvenile hormone binding protein, which is involved in metamorphosis, and genes related to signal transduction. After attachment, genes involved in developmental processes, in particular the guidance of the spatio-temporal patterns of gene expression, were upregulated, as were several cement protein homologues.
As cyprids of B. improvisus display a preference for hydrophobic surfaces at settlement, it was of considerable interest to identify genes that may be involved in the discrimination process between hydrophilic and hydrophobic surfaces. Notable genes down-regulated by exposure to a hydrophilic surface included MFS-type transporter SLC18B1 involved in the transport of biogenic monoamines, such as serotonin, and Ras-related protein Rap-2 which is a part of several signalling cascades and may regulate cytoskeletal rearrangements, cell migration and adhesion.
Finally, 291 chemoreceptor gene candidates, expressed in cyprid antennules (the appendages involved in searching behaviour), were identified. Some of these may be involved in surface selection by cyprids. In situ hybridisation studies to localise the receptors in whole cyprids proved problematic, and work continues with tissue sections, to obviate the need for probes and dyes to penetrate the cyprid cuticle.
Biocorrosion
The aim was to investigate the protective performance of coatings (a phenalkamine-cured coating, Intershield® 300; a fatty acid-modified, polyamide-cured coating Intershield® 300HS; and a pure polyamide cured coating Interseal® 670HS) against microbiologically-influenced corrosion (MIC) and in so doing, advance our fundamental understanding of this process. Coatings were applied over mild steel (CR4 grade). The approach used by TUDM was to combine microscopic, electrochemical and microbiological analyses to evaluate coating performance after immersion in three different environments: 3.5% sodium chloride solution, artificial seawater (ASW) and natural seawater (under laboratory and field conditions). Natural seawater, with its complement of microorganisms, caused a drastic reduction in the barrier properties of the coatings compared to ASW and the NaCl solution. The polyamide coatings gave the best protection against MIC. Adhesive and cohesive failures of all three coatings were noted irrespective of the solution type. Results for laboratory exposures in natural seawater were comparable to field exposures after 30 days.
Microbial fouling
BRIS carried out metagenomic analyses of biofilm formation on three biocidal anti-fouling (Intersmooth® 7460HS, Intersmooth® 7465Siand Intercept® 8000 LPP) and three fouling release coatings (Intersleek® 700, Intersleek® 900 and Intersleek® 1100SR). Six replicates of each coating (6 x 6 painted squares in a Latin square design, controlling for distance from the edge of the wooden backing panel and depth) were immersed in Hartlepool Marina in December 2014 and biofilm was sampled over four time points between March and June 2015. Identification of colonising microorganisms was carried out using multiplexed Next Generation Sequencing of bacterial 16S rRNA gene and eukaryotic Internal Transcribed Spacer (ITS) regions. More taxa, both bacterial and eukaryotic, were present on the fouling release coatings. With respect to bacteria, principal component analysis (PCoA) revealed clustering of the samples based on coating type and time of collection; clustering was less pronounced for eukaryotes. A number of issues were recognized with this experiment including the fact that the relatively static condition of exposure is not what the fouling release coatings were designed for; assaying bacteria and eukaryotes separately may have given a false impression of their relative contribution to the developing biofilm; and neither of the marker genes effectively detected archaea. A second exposure under dynamic conditions was done with coatings (2 x fouling release and 7 x biocidal anti-fouling) applied to microscope slides in the ‘Dove Lab Flume’. Slides were immersed in September 2017 and sampled at three time points during September and October. A whole-metagenome shotgun sequencing approach was then adopted. The detailed analyses have yet to be completed but a clear difference in taxonomic abundance between the fouling release and biocidal anti-fouling coatings was detected by PCoA with higher relative abundance of archaea and eukaryotes on the fouling release coatings explaining 93% of the variance. The Intersleek® coatings could also be separated with more archaea on Intersleek® 1100SR and more eukaryotes on Intersleek® 700. Gene-level analysis (BLASTX viewed in MEGAN) revealed that differentially abundant genes across the coating types were related to taxonomic abundance.
WP5 (Benchmarking & Performance Monitoring In situ)
The objectives of WP5 was to evaluate the performance of solutions developed within the technology subprojects (WP1-WP3) and which have been downselected based on anti-fouling, anticorrosion and hydrodynamic performance within WP4, in their intended working environment.
Data from all end users was collated regarding coating requirements in terms of the minimum and desirable design elements for application, performance, product features and product usage. Given the wide variety in end user requirements such as substrate material, surface preparation, expected performance lifetime and the level of acceptable performance it is unlikely that a single product/technology developed in the project will address the needs of all end users. It is more likely that different approaches will be needed or that broad technology platforms can be customized to suit the individual needs of the end users.
Application trials (substrate adhesion and cracking resistance) was conducted using the commercial benchmarking coatings and the downselected prototypes on the substrates used by the end users in order to determine suitability for them to be deployed in-field.
For the fouling release riblets approach (Modified Intersleek® Riblets) the formulation of Intersleek® was modified to make it more amenable to a mould based texturing process. Solvent content was minimised to avoid shrinkage upon cure and to ease demoulding and the thixotrope level was adjusted to obtain the correct rheology profile. Prototype paints were formulated and manufactured to enable preparation of the field trial test coupons and textured films were produced for fouling control and hydrodynamic testing using a silicone negative mould.
Environmental data acquisition devices were designed and fabricated for the purpose of monitoring the environmental parameters during the field deployment trials. Water temperature, salinity, chlorophyll level, dissolved oxygen level, dissolved organic matter and suspended sediment level (Secchi Depth) were recorded whilst the coupons were immersed using a combination of static data loggers and Earth Observation data. Custom software was written to process the data and the database updated weekly. Loggers were similarly developed and code written to support the vessel trails where geographic position and vessel speed were additionally recorded.
Coated test coupons were been prepared for all the benchmark commercial coatings. Deployment of them serving two purposes; 1) Obtaining reference performance data on the current state of the art systems in different environments 2) Creating an opportunity to practice and improve the assessment protocols and sampling procedures prior to deployment of the project prototypes. Panels were prepared with coatings which comprise a mixture of high performance biocide free fouling release coatings and biocide containing anti-fouling coatings intended for commercial shipping (marine) end use and pleasure craft (yacht) markets
13 assessments were performed on coupons deployed in the United Kingdom, Italy, Singapore, USA and Brazil. Assessment was performed using percentage coverage using visual and multispectral routes with biofilm sampling taking place to enable calibration of the multispectral images and to collect material for the metagenomics analysis of the biofilms generated (see WP4).
Additional testing coupons were immersed at the MIN testing site in Strangford Lough, Northern Ireland, these consisted of sea bed (using a mini quad pod base) and sea surface (on the surface operating platform) deployment, corresponding to 24m and 1 m immersion depths. Custom frames were designed and fabricated from galvanized mild steel for both test locations which could accommodate multiple test coupons and were rigid enough to withstand the tidal current conditions present in the Lough. An underwater locator beacon (ULB) was used to ease divers finding the seabed frame which was periodically inspected in-situ. The seabed frame was inadvertently placed in close proximity to one of the mooring chains of the testing platform, severe scratching was seen on the coatings with no observable fouling present. It was subsequently found that the surface deployed panel has become detached from the frame during the test period, this was most likely due to failure of the wooden coupon as the frame itself appeared intact, thus no coating benchmarking data was generated.
Nylon fishnet samples were coated with 3 fouling release coatings (Intersleek® 700, Intersleek® 900 and Intersleek® 1100SR and one biocidal coating (Intercept® 8000 LPP) by IP. The nets were coated by immersion into a vat of wet paint followed by removal of the excess by squeezing and then hanging. Adhesion of all the coatings was acceptable direct to the net material and whilst the flexibility of the nets coated with the Intersleek® coatings was lower than the uncoated net they were significantly more flexible than the biocidal coated net where the flexibility was reduced to a level where it made the nets unsuitably stiff. Immersion at VAL’s mid-Norway test site was conducted using a PVC frame for mounting the nets and holding them into shape. The nets were periodically assessed by measuring the amount of fouling present once a month over a 6 month period ending in mid-October the end of the fouling season in the test area. Two cleaning tests were performed with the nets being washed with different water pressures at week 19 and week 29 with water pressures varying from 20 bar up to 60 bar, and the distance between the water jet and the net panels varying between 2 cm and 30 cm. Image analysis was used to accurately quantify the amount of organic material present with the net void space and net fibre area being subtracted to give a percentage fouling coverage. At week 28 the nets coated with Intersleek® were more or less covered with mussels with the uncoated net being more fouled than the coated ones. The nets coated with Intercept® 8000 LPP had no visible fouling.
The two different water pressures used for the cleaning tests (30 and 60 bar) correspond to 8 and 12 L of water per minute respectively. After each wash the nets were lightly rinsed with a low pressure hose to displace the unattached (cleaned) material which had become entrapped in the net during the removal cleaning step. Fouling coverage using image analysis was again used to calculate the amount of fouling present before and after each cleaning pressure. It was found that at 60 bar all the commercial coatings were superior to the uncoated net and that at 30 bar the highest performing coating was Intersleek® 1100SR.
Full scale speed-power testing was conducted using International Towing Tank Conference (ITTC) recommended standards after Intersleek® 1100SR was freshly applied to the RV Princess Royal, the UNEW catamaran research vessel. During the project instrumented shafts were installed and calibrated with measurements of shaft thrust torque and speed, fuel consumption, speed over ground and speed through water then being analysed using the ISO 15016 procedure. Software was developed to post-process the measurements (normalising process) to subtract external forces acting on the vessel (wind, wave and water quality). Periodic performance measurements have been carried out after the dry-docking to determine the effect of biofilm growth on normalised ship performance.
Three Life Cycle Impact Assessments (LCIA) have been made for the prototype coatings in three end user environments with a full characterization for each downselected system. Aquaculture, marine shipping and marine renewable energy environments were analysed with comparison being made of the environmental impact (manufacture, transport, application and water resource) for each prototype product application. An environmental score card was generated for each of the downselected routes with a complete analysis from the environmental and eco-efficiency point of view using three different quantification methods (ILCD 2011 Midpoint+, ReCiPe Midpoint (I) V1.12 / Europe Recipe I and Eco-indicator 99 (I) V2.10 / Europe EI 99 I/I.).
Along the same lines as the environmental score card the eco-toxicity of each system was measured using Disability-Adjusted Life Year (DALY) to measure the years of life lost by the people, and lived with a variety of disabilities due to diseases, potentially disappearing fraction PDF*m2 per year, which measures the number of plant species that become extinct per square meter per year and MJ of energy of more than is necessary to provide per kg or m3 of mineral or fossil fuel extracted, since it will be more difficult to get them out of the nature. The different categories shown in each case are grouped into three main areas; Human health, Ecosystem quality and Resources.
For the three downselected candidates (Modified Intersleek® Riblets, Tecnoflon® Fluoroelastomers and QAS nanoparticles) flat test coupons have been prepared and subsequently immersed by IP in Hartlepool, UK, Bratton, Sweden and Changi Singapore. In each case reference coatings were immersed alongside the prototypes to enable benchmarking of the newly developed systems.
The riblet surfaces were tested in vertical and horizontal orientations and whilst the performance of both was seen to be marginally worse than the smooth Intersleek® 1100SR reference the fouling control behaviour was much superior to the smooth PDMS control (a non-fouling release test surface). The Tecnoflon® based coatings were seen to be comparable or better than Intersleek® 700 and Intersleek® 1100SR references. The coatings made QAS nanoparticles sprayed onto the surface performed no better than the PDMS control and when dispersed into the Intersleek® 1100SR formulation performance was lower than the equivalent control with no particles.
Frames holding coated net samples were immersed at the aquaculture site of VAL located in mid-Norway. The nets were commercial fish netting cut in smaller test squares with the coatings being applied by dip coating and hanging. The Modified Intersleek® Riblets were not testing due to the nets not being appropriate for a laminate foil approach thus only the Tecnoflon® and QAS nanoparticle prototypes were tested. Photos were taken of the nets once a month during the trial period (12 weeks). At the first assessment the uncoated net samples were noticeably more fouled than the coated samples, with Intersleek® 1100SR and QAS nanoparticles having the least amount of fouling (brown and green algae) which was only loosely attached. At week 12 the Intersleek® 1100SR and QAS nanoparticles still had the least fouling, while the uncoated net samples were the ones with most fouling.
Panels for hydrodynamic drag measurements were prepared to conduct boundary layer and pressure drop testing of the three downselected coatings in a clean and biofilmed condition with the biofilm being generated under two flow regimes: firstly under low hydrodynamic shear in static condition using rafts; and secondly mounted on the RV Princess Royal’s “strut arrangement” where the high hydrodynamic shear stresses accurately mimics the true in-service conditions to be experienced by a vessel. Intersleek® 1100SR and Intercept® 8000 LPP were used as the commercial standards.
WP6 (Full scale in-situ demonstration)
The objectives of WP6 served to demonstrate the scalability and fitness for purpose on an industrially and commercially viable level the prototype technologies developed within the project via application to commercial infrastructure operated by the relevant end-users with performance comparisons to current state of the art technologies.
Two paint applications to commercial, globally active container vessels of partner HLAG have been completed. Test patches (4m width and 7m height) of three benchmarking coatings were applied to develop reference performance baselines for the commercial coatings. The coatings were applied during scheduled maintenance and repair dry dockings in China using airless spray. One vessel was emergency dry-docked in Singapore 15 months after the patch applications enabling it to be inspected. Due to scheduling the inspection could only take place at night when the visibility was poor which resulted in similarly poor photo quality; Intercept® 8500 LPP was seen to be the best performing coating. The second vessel was dive inspected in Korea 9 months after test patch applications using a CCTV and photo inspection process. Intersmooth® 7460HS was seen to be the best performing coating.
Trials have been conducted in Singapore and Hartlepool, UK using a Robotically Operated (submersible) Vehicle (ROV) to conduct vessel inspections with the aim of increasing diver safety, ease of inspection scheduling and assessment quality.
Four vessel application trails and six assessments have been conducted on high activity yachts and coastal vessels. These were chosen as they afforded easier access and greater logistical simplicity than commercial marine vessels during the application and inspection process. The increased in-dock flexibility and duration allowed more in-depth studies to take place (9 coatings being applied vs. 3, biofilm sampling, multispectral imaging). To remove interperson bias, all assessments were conducted by the same assessor and to remove preconceptions concerning coating bias all the assessments were conducted blind. A weighting system associated with each “class” of fouling (biofilm, weed, soft bodied and hard bodied) was used to deduce the fuel penalty of the accumulated fouling rather than solely using the coverage of the surface by fouling. The data associated with the four vessels from 10 inspections over a 1-2 year immersion period was aggregated and Intersleek® 1100SR was determined to be the best performing coating on 7-9 knot dynamic/static cycling coastal vessels operating in UK waters.
DNA analysis of the biofilm present on the coatings applied to the four yachts and coastal vessels after their in-service period in coastal UK waters was performed. Samples were scraped from the test patches and DNA extracted using Power Biofilm kits (Qiagen). Bacterial biofilm composition was assessed by amplifying the V3 region of the 16S Ribosomal RNA coding gene and eukaryotes with the rDNA-ITS locus.
The wing of the MIN Deep Green device was coated with a modified clear coat variant of Intersleek®. Due to the need for the decorative decals to be visible an optically clear acrylic primer and Intersleek® were used. The wing was coated on both sides using a foam roller. The nacelle parts were coated with yellow Intersleek® 1100SR.
Construction of the BLUE BlueTEC device was completed in Amsterdam in March 2015 when Intersleek® 1100SR was applied to the underwater areas. It was then deployed into the water in May 2015 at the port of Den Helder, Netherlands where it was hooked up to the shore via the power and umbilical cables. After two turbine trails (4 months for the first, 7 months for the second) the device was permanently lifted out of the water. Only biofilm was visible on the device body (coated with Intersleek® 1100SR) whereas the uncoated blades were heavily fouled with barnacles and a significant amount of biofouling was seen inside the turbine itself both of which severely reduced device efficiency.
A single vessel trial has been conducted for the downselected prototype coatings. Intersleek® 1100SR, Tecnoflon® and QAS nanoparticle based paints were applied to a trawler based in the North East of the UK in September 2017. Also applied were prefabricated film laminates of Modified Intersleek® Riblets.
The tether used with the MIN Deep Green device had patches of Intersleek® 1100SR, Tecnoflon® and QAS nanoparticles applied to it. Replicate patches were placed in various positions along the tether to enable assessment of fouling challenge and coating performance across a vertical depth transect (seabed, 5m, 21m and 26m above the seabed). The tether was deployed for a 6 month period after which is was visibly assessed and sampled for DNA analysis. The coatings in the seabed area had detached due to flexing and/or abrasion so was inconclusive, at the other three depths where the coating scheme remaining intact Intersleek® 1100SR was the best and Tecnoflon® the worst performing coating.
Potential Impact:
WP1
Joint work within WP1 and WP4 has led to 1 out of the 3 technologies chosen for down-selection and field trials in WP5: the Modified Intersleek® Riblet. The development of this coating has also been identified as one of the key exploitable results of the Seafront programme.
The Modified Intersleek® Riblet was developed in WP1 and tested in WP4 and WP5. The results from the hydrodynamic and antifouling testing of this coating are very promising, showing similar drag reducing performance of the Modified Intersleek® Riblets as for the standard (non-antifouling) Dual-cure Riblets of Fraunhofer IFAM, while (after exposure to flow) the antifouling tests showed similar performance compared to the smooth (non-textured) Intersleek® 1100SR. This has a promising potential for application to moving vessels. Field tests are ongoing at the moment. A paper on the development + results from testing has been written and will be submitted soon the Biofouling, a leading journal on biofouling research.
The numerical study at TU Delft of the herringbone riblet did not reveal a drag-reducing potential. Their research on compliant coatings was restricted to very small coating displacements such that the reaction of the compliant coating could be ignored. From this study no conclusions can be drawn about the potential of compliant coatings for drag reduction, although the modelling framework developed at TU Delft provides a good starting point for future research to explore this mutual turbulence/coating interaction in relation to drag reduction. The papers that were produced in this line of research are expected to have an impact on the scientific community, in particular in the field of drag reduction research.
The research on thermoresponsive coatings by UNEW-SCL did not provide convincing evidence for improvement of the fouling release performance, although further work is recommended to better explore this possibility.
Finally, in research at TUE structure-property relationships for both non-fluorinated and fluorinated polymeric coatings were established for a wide variety of static and dynamic relief structures. New processes were explored for their low cost and large scale manufacturing. It is anticipated that the results from this project will generate new generations of drag reduction and anti-fouling coatings which, in the not too distant future, will have a positive impact on the protection of our marine environment.
WP2
The outcomes of the Seafront project relating to WP2 (Surface chemistry based) can have a significant potential impact on future improvement of the fouling control technologies.
The results delivered by this WP consisted in fact in one technology selected for field trials (the Tecnoflon® based coating) and at least other three exploitable results (PFPE-zwitterion conjugates, (nano)particles and ultra-lubricious coatings), which means a good probability that at least one of these technologies could be successfully developed in the future.
In addition, most of the formulations developed in WP2, though innovative for the chemical composition, under the coating application point of view are quite conventional and therefore easy to be applied with actual coating technologies.
Looking a bit more deeply into the detailed results, the technology which was selected for field trials (the fluoropolymer Tecnoflon®) could represent in case of success a disruptive innovation. In fact, never in the art a fluoropolymer has been applied as a coating matrix in the field of fouling release coatings, and in addition from the point of view of the Tecnoflon® polymer none of the actual applications is in the field of coating.
Obviously the timeframe and complexity of a four year project do not allow drawing of final conclusions on a single item, but just disclose possibilities which need to be further studied and in case of consistent and positive results developed under a practical and business perspective. This is the case of this coating prototype, which obviously needs to be further investigated in all the possible aspects of the formulation and the performance testing.
However, considering potentiality with the horizon of the actual data we can be really optimistic about this first technology of WP2.
Considering the other technologies classified as potentially exploitable results it is worth mentioning the PFPE-zwitterion conjugates which (at least for some selected structures) gave impressive preliminary performance results. Unfortunately such results arrived later than the deadline for deciding the prototypes to forward to field trials, so the available tests are only biological lab tests and biofilm release test. However these data are promising, being the performance equivalent to the Intersleek® 1100SR which is, to our knowledge, the top foul-release coating available. None of the other prototypes tested during the project reached this level of performance.
These PFPE-zwitterions will be investigated beyond the Seafront project and potentially they could become a future solution for fouling release coatings, especially in case they will show an advantage compared to the Intersleek® 1100SR. To fully understand these aspects we will need to scale-up these materials, investigate all the formulation and coating application aspects and also investigate performance in terms of consistency, durability, effectiveness in different fouling conditions and last but not least evaluate cost.
Another field of possible interest for this technology is coatings for biomedical applications, where there is the need to prevent contamination by bacteria and biomolecules. This PFPE-zwitterion technology may be effective also in this case, opening the road to important sustainable applications which aim to improve life to mankind.
Finally, nanoparticles based technology is another exploitable result, especially the last generation nanoparticles prepared by Fraunhofer IFAM having a hierarchical structure. The prototypes developed with this concept are under test, the first results seem promising, which could lead to a potential impact in new end user fields..
WP3
In light of the severe environmental impact resulting from the use of biocidal compounds in antifouling coatings and their consequently increasing legislative regulation, the developmental work performed within WP3 is highly relevant. The primary objective of this work package was to develop coatings with bioactive properties but zero release of toxic compounds into the environment – a challenging endeavour. While many of the devised strategies did not lead into viable coating solutions for a variety of reasons one system in fact did show competitive performance to the benchmarking coatings and was hence down-selected for evaluation in situ, namely the quaternary ammonium salts immobilized on silica nanoparticles and dispersed in Intersleek® 1100SR. The additional benefit of the QAS functionalization may lie in reduced biofilm formation particularly during inactive periods of the vessels. The system might also be suitable for application on fully stationary maritime structures, e.g. foundations of offshore wind turbines. Although it is not possible within the limited time frame of the Seafront project to fully assess the potential of this technology the prospects in terms of feasibility and economic viability are very good. The manufacturing process of the QAS-functionalized nanoparticles is already very mature and the combination with the commercial paint system can be realized at reasonable effort. Thus, in case of continued positive performance this technology could well mount into a commercial product leading to improved performance of fouling release coatings.
Although the other investigated technologies could not be advanced to a comparative level of commercially exploitable results they nevertheless provided new scientific knowledge and many of them will be taken forward in future R&D projects. The most relevant of these potentially exploitable results are outline below:
1. Chitosan. As a biopolymer and true byproduct of the shellfish industry this substance is highly interesting for various coating applications:
• Novel antimicrobial acidic chitosan coatings for hygienic, indoor, or medical applications
• (Partial) substitution of biocides in self-polishing antifouling coatings
• Replacement of fossil-based polymers in resins
2. Polyhydroxyalkanoates: These biodegradable biopolymers are highly interesting for eco-friendly coatings:
• (Partial) substitution of biocides in self-polishing antifouling coatings
• Replacement of fossil-based polymers in resins
3. Selektope®: Although the primary objective of non-release could not be achieved due to a resulting loss of function, this substance remains of high interest for antifouling coatings. Due to its non-lethal and very specific effect against animal fouling at very low concentrations it has a much lower environmental impact than many other biocidal compounds.
4. Polyglycerols: They proved to be very effective for reducing adhesion of proteins and microorganisms and are hence very interesting for antimicrobial coatings for short-term medical applications.
WP4
The laboratory-based evaluations of candidate coatings were fundamental to the successful selection of the three technologies chosen for field trials in WP5 and WP6. These assays were complemented by hydrodynamic testing of the Modified Intersleek® Riblets at TU Delft, highlighting the drag-reducing properties of this hybrid technology. The latter is the subject of a paper to be submitted to Biofouling.
Rather than standard statistical analysis of data, a meta-analysis approach was adopted to compare the performance of coatings in the various assays. This approach, which forms the basis of an article that will be submitted to Biofouling, has the potential for bringing about a step change in the methodology for efficacy testing of antifouling coatings.
Improvements to the flow cell at UNEW, including modifications to accommodate large panels, have provided a state-of-the-art testing device for pressure drop and fouling release measurements. With its ability to accommodate panels deployed on a research vessel, through a strut arrangement developed in WP5, the facility provides a near seamless means to measure the impact of real-world fouling on drag. This capability is unique and in addition to forthcoming journal publications, will have lasting impact as an analytical service to the wider research communities.
New algorithms were developed that allow the simultaneous, real-time tracking and classification of the settlement behaviour of multiple barnacle cyprids on surfaces over many hours. This advance is likely to have an impact on the scientific community interested in colonisation of surfaces, particularly since the wider utility of the method has been demonstrated for tubeworm and diatom species. The development of the algorithms and methodology was published in The Journal of the Royal Society Interface and future publications on applications of the technology are anticipated. Moreover, the methodology can be refined, based on the knowledge gained, as a high throughput means to evaluate to deterrent value of surfaces to fouling organisms.
Advances were also made in the molecular biology of fouling. A transcriptomic approach was adopted at UGOT to study differential gene expression from pre-settlement behaviour of barnacle cyprids through to the juvenile, with a number of candidate genes involved in surface exploration, fixation and metamorphosis identified. These studies are ongoing but the ‘pipeline’ for gene expression studies and the fundamental knowledge gained are highly relevant to exploring mechanisms of antifouling efficacy and thus identifying new targets for antifouling research. Indeed, the methodology will be applied to the three technologies down-selected in WP4. At BRIS, a metagenomics approach was used to investigate biofilm formation on commercial biocidal anti-fouling and fouling release coatings. Method development has enabled community analysis of bacteria, archaea and eukaryotes with clear differences in taxonomic abundance detected between biocidal anti-fouling and fouling release commercial coatings and indeed, between fouling release coatings. Gene level analysis also revealed some differentially abundant genes across the coating types. Although more work is needed, the approach should ultimately lead to a more complete understanding of the dynamic relationship between the different components of the biofilm community and targets for fouling control measures. The bacterial community analysis work has been submitted for publication in Biofouling and future publications on the wider community composition and differentially abundant genes are anticipated. More immediately, and given the importance of biofilm to marine vessel performance, a likely impact of the method development is the availability of a new analytical service.
WP5 & WP6
The innovative and unique development of low cost sensors for environmental monitoring may lead to the possibility of large scale deployment and crowd source based collection of environmental data on a global scale at high resolution. Implementation would be low cost due the selection of specific low cost sensors at the design stage. Customers and users of this could include fish farms, commercial fishermen, water utility companies, harbour authorities, ship routing systems, shipping companies and marine coating manufacturers.
The monitoring of environmental parameters simultaneously with the fouling control performance of coatings can be exploited by the permanent monitoring of water quality at test sites used to evaluate fouling control coatings. The developed low cost water quality sensors designed for deployment on static platforms would have the logged data uploaded into a central site using the software scripts written during the project from where it can be subsequently accessed. If combined with Earth Observation (EO) data, vessel track data captured from sources such as AIS and oceanographic models it could be used to determine the environmental conditions experienced by a ship, offshore platform, renewable ocean energy device or other marine based infrastructure (for example aquaculture nets) in real time anywhere.
The TeamSurv platform being worked on by SMAR could be expanded to support EO data and would enable the EO data to be tied in with in-situ measurements and vessel tracks and link with satellite derived bathymetry. The potential applications and uses for this would be marine environmental monitoring, data sets used for advising on best coating for a given location and integrating parameters along trading routes to model and analyse optimal schedules. Other applications include monitoring of algal blooms and their movement and enhanced monitoring in fish farming aquaculture applications.
The improvements and upgrades made to the RV Princess Royal to make it a fully instrumented research vessel (Strain gauges fitted to both propeller shafts to allow for high precision sea efficiency and manoeuvrability trials) enable it be deployed as a hydrodynamic analytical service to third parties or for it to be charted to conduct bespoke experiments. Marine coatings companies, naval architects, academic institutions and students share an interest in measurement of real world scenarios with a high level of precision to further understand the relationship and interactions between fouling, the vessel itself and the performance parameters.
In addition to using the vessel as a test instrument, the custom strut insert that has been designed, manufactured, installed and commissioned allows it be used as a panel deployment testbed. Deployment of test panels through the deck of the vessel ensures that the panels are deployed under genuine real world service conditions. The design uses panels which can be interchanged between deployment on the vessel or testing using other conditions. Coating suppliers, academic institutions and vessel owners would find value in using the vessel as a platform to deploy interchangeable panels for subsequent drag measurement using flow cell pressure drop or boundary laver velocimetry.
Should the testing of Intersleek® on the ¼ scale MIN Deep Green prototype demonstrate that is effective as a fouling control solution for ocean energy devices then it could subsequently be used on the full scale device with a 12m wing span. Reducing the drag caused by fouling is a priority as less drag corresponds to higher kite speed and therefore more power generated. As a further development the Modified Intersleek® Riblets could be applied to certain areas of the wing to further reduce drag beyond a hydraulically smooth surface.
The LCIA approach used in the project for the different end users with the technologies from the project has established the environmental impact of each scenario. Employing the same methodologies will be used to enable comparison of future iterations of the SEAFRONT technologies and other emerging solutions with the ones explored within the project and existing benchmarks. Additionally the methodologies will allow the addition of a new selection of materials and processes. New databases can be constructed or the existing ones modified to adapt them into other industrial sectors and quantify and evaluate the economic and societal impacts from an environmental impact and eco-toxicity point of view.
More testing in needed in aquaculture end use but the testing in SEAFRONT has shown the potential of the technologies examined. More testing is required for both the antifouling (fouling deterrence) and fouling release (fouling release/ease of clean) properties and on the process of coating large net areas. The testing methodologies involving various cleaning regimes and using photographic image analysis to determine performance could be employed in subsequent field trials. On economic and societal levels environmental friendly coatings would be welcomed by the aquaculture industry.
Marine growth can greatly impact the efficiency of tidal turbines so high performing and long-lasting coatings can assist in making tidal energy a commercially viable technology. The solutions developed in the project can also be employed for the ancillary items such as mooring lines and power cables. Floating wind turbines are an up-and-coming market that could use coatings from the project on the subsea spar area. Use of beneficial coatings would give the user an advantage over their competition. The target is to have coating product tailored toward the industry needs and environment which delivers more energy produced with less maintenance costs.
Other offshore renewable energy devices e.g. wave energy converters, tidal energy converters, offshore and onshore wind, solar and other energy sources would benefit of the drag reducing beneficial surfaces developed in the project and the economic and environmental scorecards.
Commercialization of technologies explored within the project is a realistic prospect with Confidentiality Agreements (CA’s) in place with several partners to continue the activities after the end of the project; similarly leveraged funding opportunities are being sought. Testing with end users using the SEAFRONT developed systems and commercial systems from IP will continue beyond the end of the project.
The activities within SEAFRONT have allowed IP to explore non-traditional market such as ocean energy power generation and aquaculture and non-conventional application routs in the form of laminate film.
WP7
Results of SEAFRONT have been disseminated throughout the project via publications, presentations and posters. Both academic as industrial partners have contributed to this, for instance by attending conferences in which they presented results of SEAFRONT in presentations and posters. Papers of the SEAFRONT project have been submitted to scientific journals and published. In the last phase of the project, the consortium had decided to spread its positive outcomes into a wider audience, mainly through various popular scientific media with a global reach. For this reason the consortium has made one summary text that was published right after the project.
Part of the positive outcomes of the project are possible areas for further exploitation. In the process of identifying these, a special exploitation strategy seminar was held at the end of 2016. In the last year of the project the total number of exploitable areas has grown to 19, most of which will be further developed by two or more partners of the consortium after the project. See also under xx for an extensive overview.
List of Websites:
www.seafront-project.eu