Final Report Summary - BARRIER PLUS (One component waterborne barrier coatings)
Executive Summary:
This is the final report of the European Commission Framework 7 project entitled "BarrierPlus: One Component Waterborne Barrier Coatings."
Steel is the most used metal in construction and the costs of protecting Europe’s structural steel installations and assets from corrosion is thought to be 3% of GDP (or about €375BN). However, there are two factors that will increasingly affect future protective coatings developments: VOC emissions and health/safety issues. Firstly there is a strong mandate to apply VOC emissions legislation to protective coatings (and in particular extend the Paint Products Directive to include them). Secondly REACH, together with increasing effects of chemicals on humans supported through medical literature, may prevent the use of some coating additives and formulations.
Our vision for BARRIER-PLUS is to develop one-component waterborne barrier coatings that are competitive in performance to two component coatings. One component waterborne coatings have a number of advantages over two component coatings and solventborne systems: low VOC emissions; low fire risk; lower insurance issues; no exposure to isocyanates or epoxy resins; no waste or poor film performance arising from pot life problems. Our approach is to build upon recent research in the fields of polymers and organic/inorganic nanocomposites to create enhanced film barrier properties. Although this project is focused on the protection of steel, the technology developed will have applications in the protection of other substrates, e.g. concrete, brickwork and stonework.
The project has achieved its main objective. A one-component, water-based corrosion protective coating was developed for structural steel. The waterborne polymer used in the coating was manufactured without the use of conventional surfactants. This one-component system avoids the use of isocyanates, which are commonly used in two-component polyurethane coatings. Moreover, its VOC content is significantly lower compared to a solvent-borne coating. Clear and pigmented coatings were successfully applied to steel structures. A life cycle assessment confirmed that the environmental profile of the coatings is better than a solvent-borne benchmark coating. Further work will be required to optimize the BarrierPlus technology for potential commercialization.
Project Context and Objectives:
The main concept of the Barrier-Plus project is to develop a one-component waterborne barrier coating technology for the structural steel maintenance sector. Problems with existing barrier coatings include the emission of volatile organic compounds (VOCs), flammability, short pot-life and associated wastage, and the use of isocyanates which are harmful.
Our solution is to produce a one-component waterborne paint system by blending together self-stabilised acrylic latices elaborated within Work Package 1, and polymer-encapsulated inorganic latices or Pickering stabilised latices elaborated within Work Package 2. To make a barrier coating, these particles undergo a process of evaporation, particle packing, deformation, and coalescence. The polymer molecules in the particles were reacted to bond them together to make chemical crosslinks. The purpose of crosslinking is to increase the elastic modulus, increase the coating cohesion, and to add chemical resistance. The latices were formulated with various additives and pigments to make paints in Work Package 3. The manufacturing of the latices was scaled up to make larger volumes and to move the technology towards industrial production.
The steps in the film formation process were studied in Work Package 4. The arrangement of the particles in the coating was correlated with the barrier properties. Crosslinking was confirmed through studies of the mechanical properties. The formulated paints were applied to steel structures. The weathering of the paints was studied in outdoor exposure tests and in accelerated weathering tests. The final formulated paint achieved the project objectives of being a waterborne and one-component barrier coating. Stratified coatings containing inorganic particles can provide additional properties such as film hardness (e.g. from silica) and/or UV protection (e.g. from ceria).
Project Results:
Most of the existing coatings for structural steel have two key characteristics: (1) they are deposited by dissolving the polymer binder in an organic solvent (i.e. they are solvent borne); and (2) they are hardened or cured by mixing two components. Over 88% of the global protective coatings market is based on solvent-borne technologies. A good example is a two component (2K) solvent-borne acrylic polyurethane coating. In this system, one component is a polymer resin containing hydroxyl groups, which is dissolved in an organic solvent. Before the coating is applied to a metal surface, a second component consisting of isocyanate curing agents must be added to harden the coating.
Water-based coatings account for about 12% of the global protective coatings market, but only account for about 2% of the coatings used on steel. Waterborne coatings offer several advantages over their solvent-borne counterparts, namely (a) easier clean up, generally requiring only water and (b) reduced volatile organic compound (VOC) emissions. The latter reduces potential impacts on the environment and on human health, while meeting restrictions on emissions established by legislation. Additionally, waterborne coatings are not flammable, which ensures greater safety for manufacturing centres and workers.
Converting from a conventional 2K technology to a one component (1K) formulation offers additional benefits. The use of isocyanates and related curing chemicals is minimized or eliminated, thereby reducing chemical hazards. Additionally, there is reduced waste in 1K formulations. In 2K formulations, there is a short life of the product after it is mixed (“pot life”), whereas 1K formulations overcome this challenge and can have a longer pot life.
The FP7 BarrierPlus project aimed to develop 1K water-based anticorrosion coatings for structural steel with performance equal to conventional 2K solvent-borne coatings. The project’s consortium consisted of two European associations (European Convention for Constructional Steelwork, Belgium and Norsk Stålforbund, Norway), two SMEs (Megara Resins, Greece and Tuinsa Norte, Spain), an industrial partner (Sherwin-Williams Protective and Marine Coatings, UK) and three research centres (Université Claude Bernard Lyon 1, CPE Lyon, CNRS, France; University of Surrey, UK, and CREST, Dublin Institute of Technology, Republic of Ireland). This consortium worked together to prepare unique polymers, formulate coatings, and characterize and test these systems against industry standard benchmark solvent-borne and water-based coatings.
The binder for the coatings of the BarrierPlus technology initially consists of spherical polymer particles in water, in what is known as latex. These latex particles undergo a film formation process to form a binder for a coating. The particles, typically a few hundred nanometers in diameter, are stabilized in water. When the liquid is cast on a surface, such as by spraying, the water evaporates and particles pack together. Because of the effects of surface energy, the particles deform from their spherical shape to fill the space around them. The polymer molecules within the latex particles mix with the molecules in neighbouring particles, so that the particles fuse together (i.e. coalesce) to create a homogeneous solid barrier on the coated surface.
A major problem of the conventional waterborne binder technology is that the particles are stabilized by “water-loving” (or hydrophilic) molecules called surfactants. These hydrophilic soap-like molecules can be trapped at the boundaries of particles where they can create paths for water and salts to travel through a coating to corrode the underlying surface. The surfactants can also decorate the coating surface where they can decrease the gloss, cause tackiness, and encourage dirt pick-up.
The new technology developed in the BarrierPlus project does not rely on soap-like surfactant molecules in the binder. Instead the particles are stabilized with polymer molecules. Conventional waterborne binder particles are usually synthesized using emulsion polymerization in which the particles grow from clusters of the surfactant molecules. The surfactant covers the entire surface of the particles and offers stability in water. In contrast, the particles synthesized in the BarrierPlus project have spring-like polymer molecules on their surface.
1. Latex Synthesis
Organic latexes are most of the time stabilized by low molecular weight surfactants that sit at the surface of the final polymer particles. Several alternatives have been proposed to replace them or reduce their amount to counterbalance the negative impact of their migration once the film has been formed. Ionic or ionogenic comonomers, hydrophilic macromonomers, amphiphilic (block or random) copolymers have thus been used instead. In all cases, the hydrophilic component becomes strongly anchored at the particle surface (either via covalent bond or via hydrophobic interaction and/or entanglement). Due to their heterogeneous composition distribution, very large amounts of amphiphilic random copolymers are required and only a small percentage of the chains are really efficient in particle stabilization. For amphiphilic block copolymers, the main drawbacks are the multiple step synthesis and the need for a short hydrophobic block in order to allow an easy solubilization in water.
A new way of incorporating amphiphilic diblock copolymers with long hydrophobic block, without suffering from the aforementioned drawbacks (i.e. via a single preparation step, possibility of low amounts, no problem of solubility, no remaining water-soluble species if initiation is 100% efficient) is to start the polymerization with water-soluble chains that can be reactivated for the polymerization of a hydrophobic monomer. In situ quantitative chain extension in water in the presence of the core forming monomer(s) will afford an amphiphilic block copolymer - with possibility of high molecular weight for the hydrophobic block - that will self-assemble into micelles. Those micelles can be further used as a seed for conventional free-radical emulsion polymerization, toward high solids content latexes. Such re-activatable chains (also called living chains) are easily obtained by reversible-deactivation radical polymerization (RDRP). Among the available techniques, RAFT (reversible addition-fragmentation chain transfer) is very versatile and tolerant to many functionalities and reaction conditions, allowing the synthesis of these hydrophilic living chains (named macroRAFT) to be carried out in water. In this case, the overall process of latex synthesis can be conducted in a one-pot/two-step process starting from a hydrophilic monomer and feeding the hydrophobic monomer once the water-soluble macroRAFT is obtained. Carrying carboxylate, sulfate, sulfonate, phosphate, phosphonate monomer units or MPEGMAs (methoxypoly(ethylene glycol) methacrylates) those chains hence provide the final particles not only with stability but also additional properties.
1.1. Surfactant-free Latex (WP1)
UCBL employed a strategy to obtain surfactant-free latices that was inspired by the polymerization induced self-assembly (PISA) process performed in water. This is a “one pot” process in which the water-soluble macroRAFT (i.e. an hydrophilic polymer chain) carrying an end chain active in controlled radical polymerisation (CRP) (specifically, a thiocarbonylthio group) can be reactivated for the polymerization of hydrophobic monomers. The polymerization yields amphiphilic block copolymers that can act as in-situ formed stabilizers of the simultaneously forming latex particles. In the resulting self-stabilized latex particles, this macromolecular stabilizer is thus anchored and covalently linked to the particles. These stabilizing polymers are used instead of small molecule surfactants that are typically employed in conventional emulsion polymerization.
Initially, four model latices were synthesised via the copolymerization of n-butyl-acrylate (BA) and methyl methacrylate (MMA) (referred to in the project as latices A and B) or BA, MMA and styrene (S) (referred to as latices C and D), performed in the presence of poly(methacrylic acid) (PMAA) as the stabiliser. Additionally, a model latex obtained from the copolymerization of BA and in the presence of poly(sodium 4-styrene sulfonate) (PSSNa) as the stabiliser (called latex E) was also synthesised (as analogues of Latex A and B). The PSSNa macroRAFT stabilization seems to afford more stable latices compared to the PMAA-stabilized latices.
Each of these latices fit the requirements listed in the project specifications, most notably a solids (polymer) content of 40 wt% in water. They also contain less than 1.5 wt% of hydrophilic macroRAFT agent and less than 0.2 wt% of coagulum at the end of the polymerization. Some of the resulting polymers present broad glass transition temperatures (Tg). However, additional experiments showed that the use of a semi-batch process leads to a sharp glass transition region.
Starting from these four model latices, a crosslinking strategy was implemented to confer improved properties to the films formed from the latices. Three crosslinking strategies were employed and investigated. Strategy (1) leads to an internal crosslinking performed prior to the film formation while strategies (2) and (3) concern self-crosslinking reactions occurring during film formation.
A series of internally crosslinked latices were obtained via the introduction of 1,3-butanediol diacrylate (BuDA) as a co-monomer. However, because the particles were internally crosslinked, the interdiffusion of their constituent molecules was restricted. Furthermore, there was no crosslink formation between the particles within the film. Hence, weak and brittle films resulted. Consequently, this first strategy (1) was set aside and not investigated further.
The second strategy (2) used to obtain crosslinked films is based on the reaction between ketones (either diacetone acrylamide, DAAm, or acetoacetoxy ethylmethacrylate, AAEM) in the presence of reactive additives (a dihydrazide or a diamine) during film formation. Thus, both DAAm- and AAEM-functionalized latices based on the various original models have been synthesized and delivered. The final strategy (3) envisioned for the formation of crosslinked films relies on the introduction of a silane monomer during the emulsion polymerization. The functionalization of latices B and E using a silane co-monomer has been carried out and the samples sent to other partners for applications in coatings. The use of a semi-batch process resulted in polymers with well-defined and sharp glass transitions. The particle size was also decreased.
Concerning Strategy 2, tests on latices A-, B-, C- and D-type were carried out. Due to some opacity observed when forming films out of latex C, this one was set aside. Thus, different samples based on latex A, B and D were supplied to the other partners of the project. A new latex composition based on latex D, but stabilized with only 1.0 wt% of PMAA instead of 1.5 wt% was also developed and supplied. The objective was to reduce the amount of hydrophilic component.
For the AAEM/diamine strategy, latices stabilized with PMAA macroRAFT agent were delivered (A-, B- and D-type). A new latex containing more MMA than latex D (BA/S/MMA 55/10/35 wt% instead of 60/10/30 wt%) and less macroRAFT agent (1.2 wt% instead of 1.5 wt%) was developed.
1.2. Polymer-Encapsulated and Pickering Stabilised Latex Synthesis (WP2)
Hybrid latices based on the encapsulation of silica, ceria or titania have been synthesised. Silica (40-100 nm) encapsulated latices have been synthesised by a conventional route involving surface modification and surfactant stabilisation. This approach gives (single core)- shell hybrid latices with 20 wt.% solids content and particle sizes in the order of 100 nm. The final latices reach a limit around 30 wt% solids before significant coagulation is produced. Incidentally, a (multi core)-shell morphology due to particle coalescence is evident at a solids content close to the limit of instability.
The encapsulation of ceria and titania have been achieved through the use of macroRAFT-mediated emulsion polymerisation. Applying the same methodology to silica was unsuccessful due to poor interaction strengths between the macroRAFT agent and silica. The encapsulation of ceria (7 nm) has resulted in (multi core)-shell hybrid latices. Hybrid latices with particle sizes on the order of 500 nm have been synthesised. While targeting solids content greater than 30 wt.% results in high amounts of coagulation during synthesis, the formation of foam with samples containing 30 wt% solids content has further lowered the usable solids content to 20 wt.% for this system. Titania (400 nm) was encapsulated with a thin (15 nm) polymer shell surrounding individual titania particles, but large amounts of irreversible sedimentation was observed. Due to these instability problems, the model samples have been re-assessed to compromise the solids content for long-term stability. Long-term stability tests of the latices were introduced to guard against the problem.
Pickering-stabilised latices based on ceria and clay were also synthesised. Obtaining latices armoured with silica was less successful due to the poor interaction strengths between the polymer and silica. Hybrid latices using negatively charged ceria (7 nm) as a starting material allowed the formation of latices with up to 30 wt% solids content and large particles on the order of 800 nm. Due to the large size, the morphology cannot be ascertained. By using positively-charged ceria (7 nm), hybrid latices with an unquestionably armoured morphology were obtained with 30 wt.% solids content and particle sizes around 400 nm. However, instability was observed at pH > 7, which is problematic for paint formulations unless the charge on the particles can be inverted without irreversible aggregation. Latices armoured with clay platelets have also been synthesised with 20 wt.% solids content with 400 nm individual particles and some aggregation.
In general, hybrid latices with a minimum of 20 wt% solids content were obtained with most systems approaching instability at 30 wt% solids content. Pickering latices have reached 35 wt.% solids content (e.g. AC25) at which point a higher solids content produces high coagulation. As considered in the risk assessment, the use of lower than 40 wt% solids content is viable provided that the barrier property performance is good. To this end, samples AC12 (CeO2, encapsulation), AC19 (CeO2, Pickering), and MP-26 (clay, Pickering) were selected for further development as coatings.
All of the latices form films within the desired range of 0-25 °C allowing them to be studied for their barrier properties. All samples of encapsulated latices have sharp glass transition temperatures in the intended range for film formation at room temperature. Samples of Pickering latices have glass transitions that are significantly broader in temperature; nevertheless the minimum film-forming temperature experiments demonstrate film formation slightly below room temperature.
Ceria encapsulated, ceria Pickering latices, and clay Pickering latices were re-synthesised for film testing. In addition, internal and external crosslinking functionality were implemented. With concerns over the practicality and upscaling of synthesising encapsulated latices through a macroRAFT mediated strategy, as well as pressure to supply samples for the project work flow, subsequent work was concentrated on Pickering latices. Consequently, the number of Pickering latices supplied was greater than the target number, but the number of encapsulated latices supplied was approximately one-half of the target number.
The implementation of a semi-batch monomer feed gave more stable clay Pickering latices, which improved the films’ characteristics, such as transparency and texture. Implementing the semi-batch monomer feed, a range of samples were synthesised and characterised. Internal and external crosslinking functionality was also implemented.
A variation on the recipe of clay Pickering latices removed the auxiliary comonomer (PEGMA) and resulted in stable latices with a subtly different morphology (namely, smaller particle sizes and ‘less armoured’ per particle). By exploiting this variation, the size of the particles was fine tuned. Also, new information was obtained on the effect of the clay, auxiliary comonomer, and the morphology, on the film properties. This new approach also showed promise in reaching the targeted 40 wt% solids content. Solids content were increased to 35 wt%, although 30 wt% is recommended to avoid coagulum. For crosslinked films, gel fractions were increased using silane external crosslinkers. Various samples (including external crosslinking) were synthesised with solids content of 35 wt%.
While latices with 40 wt% solids content have not been achieved, mechanistic studies provide guidance towards further improvement. Mechanistic studies were performed on the synthesis of clay Pickering latices in order to increase solids content. Generally to obtain a stable latex, coalescence of particles should be minimised by exploiting the charge stabilisation of clay platelets. PEGMA reduces the effectiveness of clay as a stabiliser by screening charges. A slow monomer feed can allow time for the clay to reorganise and be more effective as well as reduce the number of monomer droplets which can interact with clay. Stirring also should be considered as it impacts particle collisions (and therefore coalescence), but a minimum speed is needed to aid monomer diffusion into the polymer particles.
It was found that various parameters can be tuned for a more fine control of the size of particles: by monomer composition in the case of ceria, and auxiliary comonomer and clay concentration in the case of clay.
Internal and external crosslinking have also been explored with various systems, but mostly clay Pickering latices due to the easier characterisation and ease of synthesis. 1,3- Butanediol diacrylate (BDA) and a functional silane monomer were effective at giving internally and externally crosslinked films, respectively. Gel fractions were calculated for all crosslinked Pickering latices, and was found to be particularly low for the silane-functionalised clay Pickering latices, which suggests that this system can be further improved.
Subsequently, self-crosslinking (MPTPS) ceria encapsulated latices were synthesised, based on the existing model samples to allow film comparisons to be made. Investigation of an inexpensive macroRAFT approach (use of PSSNa-CTPPA) to encapsulate ceria clusters using internal crosslinkers failed due to early aggregation. P(SSNa-stat-BA)-CTPPA macroRAFT agent was used to encapsulate ceria as a proof of concept and was successful, however this alternative approach can be optimised. Efforts to encapsulate clay through the use of PSSNa macroRAFT agents allowed us to obtain ‘dumbbell’ morphologies (i.e. clay platelets sandwiched by two polymeric nodes). Since the approach is less cost-effective than clay Pickering emulsion polymerisations and is limited to solid contents ≤ 20 wt%, benefits of this morphology requires justification.
To obtain a ‘true’ ceria Pickering latex which is stable in basic conditions, a different ceria source was used in conjunction with PSSNa-CTPPA to prevent clustering of ceria. Unfortunately, this idea was unsuccessful and the ceria lacked interaction with the polymer latex. Additional investigations were performed on blends of ceria, first to study the impact on a film between using a pre-assembled armoured structure compared to blends with ‘blank’ latices, then also as a means to introduce ceria to the polymer latex. More specifically, blends were made of ceria with macroRAFT-based latices from WP1, as well as blends of acidic sol Pickering latices with macroRAFT-based latices. While this route worked to an extent, the charge-inversion route with poly(acrylic acid) showed more promise towards ‘truly’ armoured ceria latices stable in basic conditions.
In summary, ten polymer-encapsulated latices have been synthesised and delivered as follows: four silica-encapsulated; one titania-encapsulated; and five ceria-encapsulated latices. A total of 23 ceria Pickering and 27 clay Pickering stabilized latices have been synthesized and delivered, including two crosslinked ceria Pickering samples and seven crosslinked clay Pickering samples.
2. Formulation
Throughout the formulation trials, several different additives were used for various purposes. The additives included a pigment dispersant, a defoamer, a surface tension modifier, flash corrosion inhibitor, a UV stabiliser, co-solvents, a rheology modifier, pigment, a corrosion inhibitor, an extender, and a filler.
A total of 70 formulations (clear and pigmented) were prepared, using the surfactant-free latex. Selected formulations were screened and evaluated using Electrochemical Impedance Spectroscopy, UV stability tests, and laboratory environmental corrosion tests.
After screening the various formulations, one clear and pigmented formulation was selected for scale-up for weathering testing. It was Latex A (JLH 268) with AAEM functional groups for crosslinking with HMDA.
The synthesis of six latexes were scaled-up to the laboratory (or pilot) scale at Megara and evaluated for formulation as both clear coats and pigmented coatings. These latexes are:
(1) Latex A + DAAM--JLH250
(2) Latex A + AAEM- JLH278
(3) Latex G + AAEM- JLH268
(4) Latex B + DAAM- JLH234/229
(5) Latex B + AAEM - JLH227
(6) Latex E + AAEM - JLH266
Thus, a total of twelve candidate coatings formulations were produced, which exceeds the eight formulations that were set as the original target. Three formulations were selected as being the most suitable for application testing. These final formulations required the addition of the HMDA cross-linker before outdoor weathering testing.
The stability of AAEM formulations containing the HMDA additive was studied. It was found that the BarrierPlus clear and pigmented formulations were indeed stable as a one-component formulation. Hence, the main objective of the project was achieved. This formulation was deemed to be suitable for C2 environments, which are exterior rural areas with low pollution, according to the ISO 12944 classification.
Issues observed included:
• Foaming during manufacture of clear or pigmented (and latex) which then dries to a very brittle film forming an insoluble crust, which breaks down easily.
• A tough hard settlement forms with the clear coats, which was not dispersed without high speed mixing, which can then induce undesirable foaming.
• A sharp drop in pH was observed with both JLH 268 and JLH 278 clear coats during a short storage period (5 days) at ambient temperatures. This sharp drop led to an irreversible particulate sediment forming in the delivered JLH 268 material.
• The JLH268 clear formulation is not stable at 5°C. Therefore it is not freeze/thaw stable and would suffer during winter storage.
• After five weeks of storage, the pigmented JLH278 was stable with a slight increase in viscosity at both 52°C and 5°C with no sedimentation observed.
Conclusions that can be drawn include:
• A further study of the clear formulations is required to develop a product with a sufficient shelf life that maintains a constant pH, which may be achieved using more suitable amine alternatives.
• The development of latexes requires more scale-up trial data through Megara Resins, which would be realistic of large-scale manufacturing conditions.
3. Film Formation and Properties of Latex Films
3.1. Experimental Studies of the Drying and Particle Packing in Particle Blends (WP4)
Experiments were conducted to understand the influence of different parameters (such as the presence, chemistry and amount of surfactant or macroRAFT agent in the latex synthesis, the size and number ratio in particle blends, and the annealing temperature) on the film formation process of coatings. Microscopies have been used as appropriate.
Film formation consists of three main processes: (1) water evaporation and particle packing; (2) particle deformation; (3) interdiffusion and coalescence. The introduction of macroRAFT agents in latices synthesized in WP1 were found to slow down the drying (water evaporation) process of coatings when compared with latexes made with surfactant or MAA stabilizer. Using a less hydrophilic macroRAFT (based on PSSNa) helps to reach the drying plateau faster than when using a more hydrophilic one (based on PMAA). The introduction of clay in the Pickering latex (5 and 10 wt.%) also slows down film formation when compared to a blank latex.
The difference in the barrier coatings made from surfactant-free particles is immediately apparent when examined at the sub-micrometre scale using an atomic force microscope. In a conventional waterborne coating, the surfactant was seen to accumulate in droplets on the film surface when aged at elevated temperatures. The surfactant-free coating made in the BarrierPlus project, on the other hand, has a more homogeneous surface structure and is more stable when aged.
Small angle neutron scattering (SANS) was used to follow in real time the last stages of film formation (coalescence and phase inversion) in macroRAFT (surfactant-free) and in surfactant-containing films. The data show a shift to lower wave-vector (q) along with a loss of peak intensity, which are changes attributed to the decrease in the particle spacing with water evaporation, followed by close-packing, and particle deformation. MacroRAFT samples annealed in the range of 100 to 200 °C show a distinct feature of 30-40 nm in size, which was also visualized via AFM images and identified as macroRAFT domains. This result shows that the macroRAFT agent does not form a continuous network throughout the coating when annealed. The water barrier properties of the coating might benefit from not having a continuous hydrophilic path from the top surface to the substrate. Surfactant, in comparison, formed blob-like structures on the films. This increased mobility surfactant compared with macroRAFT agents, and the rearrangement of surfactant into clusters, could be detrimental for water barrier properties.
Film formation studies in bimodal colloidal mixtures revealed a stratification effect. The smaller particles excluded the larger particles and formed a layer at the top of the drying film, as we demonstrated using AFM and confocal laser scanning microscopy. This newly-discovered mechanism will be useful whenever the properties of the top and the bottom of a coating need to be controlled independently via a one-step deposition process.
A binary colloidal system that allows self-stratification during drying can be "switched off" using pH as the trigger. Coatings are stratified when cast from dispersion with a pH below 7, but the effect is lost at higher pHs. The stimuli-responsive polymer colloids, synthesized in WP1, increase in size when the pH is raised. This switch off is explained by the combined effect of a decrease in the particle size ratio, an increase in the total volume fraction and a decrease in pressure gradients. Langevin dynamics simulations showed that when the particle size increases above 80 nm, the stratification is suppressed, which agrees remarkably well with the experiments. Achieving such control over the stratification process allows not only the independent programming of the properties of the top surface, but also the possibility of switching the surface properties without changing the starting materials.
3.2. Structure and Barrier Properties (WP4)
Experiments were conducted to understand the nano- and microstructures of the dry, film-formed waterborne coatings, and then to correlate the structures with barrier properties. Microscopies were used as appropriate. Additionally, water was used as a probe of structure via the characterisation of the states of water (dissolved, bound, freely-diffusing) within the coatings.
The characterization of surfactant-free latices synthesized in the presence of macroRAFT reveals that they show better barrier properties as measured by lower water sorption (from both liquid and vapour) and adhesion than control latices synthesized via standard emulsion polymerization using the same compositions. Comparison of the samples suggests that the amount of macroRAFT agent and its hydrophilicity are key parameters in the barrier properties of the coatings. The use of magnetic resonance relaxometry allowed the characterization of the distribution of water after soaking of the films, revealing that a less hydrophilic stabilizer leads to smaller water clusters. Atomic force microscopy was used to determine the structure of packed particles during coalescence. Water vapour sorption experiments show that the hydrophilic species are less accessible in macroRAFT latex films than in standard emulsion polymerization films of the same nominal composition.
The surfactant-free binder technology developed within the BarrierPlus project offers some obvious benefits in preventing the penetration of water through barrier coatings. When one of the surfactant-free 1K coatings, developed in the BarrierPlus project, is soaked in liquid water for one day, it absorbed approximately 17 wt% water, which shows it has poor suitability as a barrier coating. The stabilizing molecule on the particles in this formulation contains carboxylic acid (-COOH) groups in this example. However, when the stabilizing polymer molecule is substituted for another type of stabilizer without -COOH, only about 2 wt.% water is absorbed, after an initial uptake when first immersed in the water, which makes it more suitable for a barrier coating.
When a conventional waterborne (latex) coating is soaked in water for prolonged times, it becomes opaque because water penetrates the coating where it creates small droplets that scatter light. This phenomenon is referred to as “water whitening” in the coatings literature. The BarrierPlus coatings prevent water from penetrating, and they stay optically transparent even after soaking in water for up to three hours. The original latex composition displays evidence for water whitening, as the optical transparency decreases strongly over time. When a different stabilising polymer is used in the latex synthesis, there is very little water whitening. The superior properties of this BarrierPlus technology is apparent.
The 1K coatings technology developed within the BarrierPlus project uses particles that have chemical groups that react with molecules in the water phase (so-called crosslinkers) during the drying process. With added crosslinkers, the coating becomes harder, more scratch-resistant, and has improved barrier properties after curing.
Our studies show that the addition of cross-linking functionality to the latices can be either detrimental (if the latex particles are internally cross-linked) or beneficial (if the latex particles self-cross-link during film formation) for mechanical properties of the coatings and the retention of optical clarity. However, all of the cross-linking functionalization carried out within WP1 result in an increased amount of water sorbed upon soaking. External cross-linking of the macroRAFT latices via DAAm functionalization slows down water whitening considerably and improves the mechanical properties of the coating. However, the amount of water sorbed after 72h is higher than that of the blank. External cross-linking of the macroRAFT latices via AAEM functionalization does not improve significantly either the water barrier or the mechanical properties of the blank latex. Silane cross-linking slows down the water whitening process slightly and improves significantly the mechanical properties, except for the strain at failure which is reduced.
Our results show that the impact of the addition of ceria nanoparticles on the coating properties depends strongly on the ceria distribution within the coating. True armoured morphologies, such as obtained in the Pickering latex synthesized in WP2 using an acid ceria sol, where every latex particle is surrounded by ceria nanoparticles, show the best combination of high absorbance in the UV region and high visible transparency for coating applications. Also, the addition of ceria raises the storage modulus significantly at temperatures above Tg. However, when there is a significant amount of free ceria (such as in the Rhodigard ceria Pickering latices synthesized in WP2) there is a significant loss of transparency in the visible region. Optical properties were correlated with the structures determined using atomic force microscopy and electron microscopy. Moreover, the addition of ceria results in lower water content after soaking for 72h in comparison to the standard latex.
In Pickering clay nanocomposite films, the sorbed water is weakly bound, perhaps because of the nonpolar inorganic interfaces. Upon heating, the water is readily liberated. Latex films without clay particles retain water for temperatures as high as 200 °C. The 5 wt% clay samples (also the internally cross-linked latex) become opaque when soaked in water (i.e. “water whiten”) and then become transparent again with continuous soaking. This is a very unusual behaviour that could be related to a structural change.
3.3. Modelling of Film Formation
The modelling activity has been divided in three components: (1) Packing of mixtures of latex particles of different sizes; (2) calculation of the distribution of the length and diameters of the channels in the final film; and (3) deformation of the particles with viscoelastic flow.
3.3.1. Packing of mixtures of latex particles of different sizes
We studied coatings obtained from drying films containing mixtures of particles of different sizes. During evaporation the film’s air-water interface moves towards the bottom substrate. With computer simulations and theoretical modelling we have studied the drying process and the structure of the dry film. The initial study was carried out for two-component systems, i.e. a mixture of large and small model latex particles. We found that, when the number of small particles is larger than a critical value, the film stratifies into a layer of the larger particles at the bottom with a layer of the smaller particles on top. This is a potentially useful finding as stratified coatings could have novel properties, and will affect its barrier properties. The preponderance of small particles near the top of the film leads to smaller channels there and hence potentially better barrier properties to water ingress, of that part of the coating near the top surface. Hence, this finding was used as input into coatings studies at Surrey (with particles from Lyon), and these coatings studies verified our modelling predictions. The modelling predicted that if the particles were colloidally stable, that particle size was the dominant parameter, e.g. the effect would be found for conventional latices, surfactant-free latices, and those with and without inorganic material. This input informed particle synthesis at Lyon.
We developed a theoretical model to show that a gradient in osmotic pressure, which develops dynamically during drying, is responsible for the segregation mechanism behind stratification. The formation of stratified films was quite unexpected, therefore we investigated the formation of stratified layers in three-component systems, i.e. ternary mixtures of model latex particles of different sizes. The segregation mechanism was found to be important in ternary mixtures as well. The large parameter space available during formulation allows for a great control of the structure of the dry film. The modelling and simulation work on two-component systems reported here was published in Physical Review Letters in 2016.
The study of the packing of model latex particles in multicomponent systems was continued with studies of mixtures of polydisperse latex particles. The segregation mechanism was found here as well, but it has only a minor influence on the structure of the dry film.
3.3.2 Calculation of the distribution of channels in the film
A novel algorithm was developed to scan for empty spaces in the packings of dry films. The network of voids and channels was approximated by a collection of spheres. Cluster analysis was used to determine the structure of the network of channels. We found that the size of the largest voids is related to the size of the smallest particles. Furthermore, we found that the size and number of voids is larger nearer the substrate.
If small particles with attractive interactions are used in the composition, the resulting dry films have more voids and channels than dry films of purely repulsive particles. These attractive interactions model particles with reduced colloidal stability. Our models show that the size of the largest void, the number of voids, and the radius of gyration of the largest cluster of voids, i.e. biggest channel, are all smallest for particles with purely repulsive interactions. This is at the end of the packing of particles together caused by drying, but before coalescence. Thus for our mixed systems of particles, our modelling predicts that any attractions between the particles tend to create potentially problematic larger voids and channel. This suggests that barrier properties are optimised by minimising any attractions between the particles.
3.3.3 Deformation of particles with viscoelastic flows
The effect of particle deformation was investigated by discretising each latex particle into mobile
elements. These elements interact via an attractive interaction, and an elastic force. The dynamics of these elements, which leads to deformation of the particles, was modelled by a lattice dynamics. A ripening or coarsening of the voids driven by the minimisation of the surface free energy was found. The largest voids grow in size at the expense of the smallest voids. In perfectly ordered close-packed crystals, the coarsening leads to a reduction of the size of the network of channels connecting the top to the bottom of the film.
The deformation simulation was applied to the final particle packings found in our simulations of drying (which were far from perfect crystals). In these systems ripening leads to an increase in connectivity between different voids, leading to a percolated network of channels from the top surface of the film to the bottom substrate. The number of smaller voids was found to decrease during ripening. Also notable is that although introducing attractions between the particles, i.e. making the particles less colloidally stable, alters the pore structure before particle coalescence, the process of coalescence greatly reduces the difference attractions make to the final pore structure. This suggests that there should be a relatively large window of particle-particle interactions over which the final pore structure is invariant.
4. Weathering Testing
4.1 Application of Coatings
Prototype steel structures were coated and evaluated in terms of (1) Sag Resistance, (2) dry film thickness (DFT) and uniformity, and (3) Physical performance.
The performance of the Latexes JLH 278 and JLH 268 in pigmented and clear coatings was good in comparison to the commercial benchmarks. In particular, it was found that:
(a) Sag resistance was good with no running.
(b) The dry film thickness was controllable and within the expected range, while the coatings showed evidence of good edge coverage.
(c) The adhesion of JLH 278 (pigmented) was found to be good, achieving a rating of 1. JLH 278 (clear) adhesion was very good on direct-to-metal primer coatings and a 2K Epoxy (both rated 0) but poor on a JLH 278 coating (rating 5).
4.2 Corrosion Testing
The Barrier Plus samples with the JLH 278 pigmented base were all observed to corrode within the first cycle of D5894 testing without a scribe. The 2K Epoxy/JLH278 clear coatings developed corrosion spots following QUV accelerated weathering, but these didn’t degrade following cyclic corrosion tests. The JLH278 and JLH268 clear coatings on direct-to-metal primer samples maintained appearance with a small change in gloss. This is a promising result for the BarrierPlus materials.
In outdoor weather tests, the BarrierPlus pigmented and clearcoat coatings have so far performed favourably against the industrial benchmarks. Although weaker than the epoxy primed surfaces, the Barrier Plus systems are better than the Acrylic DTM systems in preliminary results. The outdoor weathering tests are ongoing.
4.3 Life Cycle Analysis
It was found through a life-cycle analysis that the BarrierPlus coatings had a lower environmental impact than benchmark solvent-based coatings. The commercial costs of the technology were investigated but cannot be determined until industrial-scale production is possible.
Potential Impact:
1. Impact
When a commercial product is developed from the BarrierPlus technology, it will have a number of competitive advantages over existing solvent-based and two-component systems:
- Lower health and safety risks;
- Reduction of maintenance times by improved barrier properties;
- Non-flammability;
- Lower VOC emission and compliance with REACH Legislation;
- Reduction of litigation risks in case of incorrect coating application.
The new coatings technology developed in the BarrierPlus project has the distinct potential to have economic, environmental, and societal impacts. Each type of impact is considered separately hereafter.
1.1. Economic Impact
The BarrierPlus technology, as developed in this programme, will primarily impact two commercial sectors, the structural steel sector (construction) and the protective coatings sector. There are likely also secondary project benefits that could impact the paint contractor industry and personal protective equipment sectors. But the focus here is on the overall effect likely to be achieved in the global protective coatings industry sectors intended for corrosion protection of large-scale, steel engineering structures. The global market segments affected are large in scope, and specifically in Europe, steel remains a key part of the European industry value chain with continuing yearly revenue streams in excess of € 3,000 billion, and employing 23 million people. All steel thus used must be protected from degradation and corrosion, and this is where the BarrierPlus technology can become impactful in the future. Recent market studies project that the global market size for such anti-corrosion coatings is estimated at € 18.4 billion, which is projected to grow to €26.5 billion by 2021 with a compound average growth rate (CAGR) of 5.1% between 2017 and 2021. From these projected values, products based on the BarrierPlus technology could well have a significant economic impact in the future, assuming the products thus developed function in ways that have commercial viability.
The coatings developed in the Barrier Plus project have potential to make an economic impact in the form of new products on the market. The market viability of any new product is always a function of the costs involved to produce, distribute and sell the product. In turn, these factors determine the eventual selling price for the product. All such cost factors must be manageable for a new product ultimately to be successful both in the European, and also in the global marketplaces. Manufacturing and supply chain cost analyses have been conducted. In this work, Megara Resins addressed the base resin manufacturing engineering and cost considerations of the BarrierPlus acrylic-latex materials. Market viability assessments for fully formulated paint products using the Megara-generated acrylic-latex resins were produced. Base resin manufacturing costs addressed in this analysis included variations needed in capital manufacturing machinery, as well as factory equipment adjustments needed for BarrierPlus technology differences when compared with more traditional manufacturing procedures for solvent-based paints and also for more traditional acrylic-latex manufacturing procedures.
In the BarrierPlus latex, the use of the macroRAFT agent increases costs in comparison with preparing the same latex with conventional free-radical polymerization and the appropriate emulsifier. An indicative assessment of costs for the macroRAFT latexes gave an estimated price that is significantly higher than a conventional industrial latex grade. MacroRAFT containing latexes have an estimated cost that is about 10 to 15 times higher than the cost of a conventional acrylic latex. This is due to the cost of the macroRAFT agent.The macroRAFT agent is a key chemical reagent necessary for the preparation of the surfactant-free latexes. MacroRAFT is not available as a commodity chemical. During the research phase of the BarrierPlus programme, UCBL were able to synthesize the chemical reagent (“RAFT agent”) for use at the research scale. 4-Cyano-4-thiothiopropylsulfanylpentanoic acid (CTPPA) was obtained by reaction of ACPA with bis(propylsulfanylthiocarbonyl) disulfide. However, much larger quantities are required for the scale-up for industrial manufacturing. Therefore, multiple quotations for pilot-scale quantities of RAFT agent were obtained and the lowest price option was selected for scale-up work. It should be emphasised that whilst the raw materials pricing considered in this report used the macroRAFT materials as purchased for this project, custom chemical manufacturing is significantly more expensive than eventual commodity production, the latter of which will likely be needed to achieve full commercial viability.
Differences in paint product formulating and manufacturing costs, as well as distribution and sales costs have also been addressed in order to evaluate the overall cost effectiveness expectations and likely final pricing of the BarrierPlus technology. Furthermore, the technology associated with BarrierPlus should add little if any complexity or cost to the eventual paint manufacturing and distribution business function, when the base acrylic latex paint ingredients are supplied for paint manufacturing.
The significantly higher cost of the macroRAFT-based latexes does not necessarily preclude BarrierPlus technology from market viability. If paints forumulated using BarrierPlus latexes exhibit paint performance properties for durabilty and corrosion protection that are equal to, or better than, the 2K solvent borne products that are in widespread use today, then there will be strong interest from the market for the new technology. Furthermore, in general, the cost of the paint resin (i.e. ‘binder’) which acts to hold together all the ingredients deemed necessary to make a successful paint, is typically the most expensive single formulation ingredient, and its cost can be mitigated somewhat by the use of necessary paint raw materials that are less expensive (e.g. use of low cost pigment extenders such as platy micas used to provide improved barrier properties to the paint so as to limit the ingress of water, oxygen, and corrosive species through the paint).
The original commercial objective of this project was to supply a one component waterborne barrier coating performing as well or better than a comparable two component system at a cost of no more than €10 per litre. The average anticipated costs for formulated pigmented and clear BarrierPlus coatings are reasonably in line with epoxy and polyurethane cost structures of typical products used today, thus meeting the project’s objective.
A further consideration is that the 1K BarrierPlus technology inherently results in a simpler paint technology option compared with today’s 2K solvent based epoxy and polyurethane options. The key difference is that the acrylic has only one component and does not require the complexity of a separate paint component for chemical curing processes.
Although final costings cannot be estimated at this time, the BarrierPlus technology will inevitably result in considerable overall job cost savings in terms of ease of paint application using simple brush, roll and airless spray equipment, rather than contractors having to mix components A and B, with the possible further need to use complex spray application equipment such as plural component equipment. With BarrierPlus technology, 1K products will have a longer potlife than today’s 2K solvent borne paints, which will also reduce unusable or waste paint, thereby reducing overall job costs.
In summary, although the BarrierPlus resin costs initially appear to be uncompetitively high, the overall cost considerations for broader commercial viability do not preclude use and consideration for future commercial exploitation.
The overall cost calculations and long term commercial viability for the BarrierPlus technology will ultimately be a function of the demonstrated product performance capabilities of the finished paints. In this respect, ongoing data produced in the BarrierPlus consortium program as described in Work Package 3 will likely be the determining factor for future technology success. If BarrierPlus technology can be shown to be superior to today’s solvent-borne products, then significant market penetration is likely in the future.
It should, however, be noted that the adoption of any new technology in this and other related structural steel markets must be tested and approved to industry standard specifications. Technology adoption rates for high performance paint requirements are expected to be slow initially. Initial years of commercialization would be limited to further testing and validation of coatings performance properties when exposed in real-world conditions. Nevertheless, expected coating sales values would still be substantial and of considerable benefit to society in general.
1.2. Environmental Impact
The coatings developed in the project have the potential to make an environmental impact. In a full Life-Cycle Assessment, BarrierPlus coatings system performed better than the solvent-based system and showed promising results relative to commercial waterborne benchmarks.
The bulk of the environmental impacts for each system were from the creation of the pigments and resins. The solvent system also had significant impacts due to the use of conventional solvents (as opposed to water). Typically, titanium dioxide was the single largest contributor across all impact categories for each product system. Transportation, packaging, disposal, and manufacturing were relatively minor contributors to overall impact. Application impacts were negligible unless the product contained a significant amount of VOC, which was then assumed to be emitted during the use phase (causing a spike in photochemical ozone creation during this phase).
In order to put the Life Cycle Impact Assessment (LCIA) results in context, the impacts for 4 m2 of steel plate was considered. The 4 m2 area selected is a conservative estimate of how much metal substrate would be covered by the coating systems given the functional unit of this study. This is to say that this value reflects expected coverage area from 1 kg of both the basecoat and the topcoat. Given that BarrierPlus and the coating benchmarks are designed to protect metal substrates, this metric showcases the importance of such coatings, as the metal substrate exhibited impacts around an order of magnitude higher across several key impact categories. The only indicators where the coating products were expected to have higher impacts were ozone depletion and smog formation. The latter of these is unsurprising given the VOC content of the coating products.
Given that BarrierPlus is only being made at a laboratory level scale, it was unsurprising that it had higher impacts than comparable water-based chemistries made through large-scale production channels. It is worth noting that some of the results were not statistically significant, especially toxicity. Taking this into account, BarrierPlus had an overall comparable environmental profile to the conventional water based benchmarks even if its impacts tended to run slightly higher than those benchmarks.
Interestingly, one of the primary impact drivers of BarrierPlus was the anti-corrosive pigment used in the formula. If this is able to be substituted to another raw material, BarrierPlus could reduce its impacts by 10-20% in certain impact categories. If this were to occur, BarrierPlus may become essentially equal in environmental impact to the water-based benchmark systems.
Toxicity in general is a problematic indicator given its high uncertainty. In addition, USETox was not able to take into account the fact that the surfactants found in several common resins were eliminated from the latex systems. Since no specific characterization factors for these chemicals currently exist in USETox, the models were not able to capture this distinct benefit.
Since no field study performance results were available for BarrierPlus at this time, it was assumed that all systems were performance-neutral. In reality, some of the systems may perform better or worse relative to BarrierPlus. A scenario was considered where BarrierPlus achieved 50% better performance than the benchmark systems.
High performance is key when considering overall environmental impact. If BarrierPlus was to have 50% better performance than the benchmarks, it performs equivalently or better in each indicator. This shows that any significant performance gain under the BarrierPlus product system leads to an overall environmental improvement. As such, care should be taken to ensure that the performance of BarrierPlus be as optimized as possible and the LCA models should be reassessed once actual performance data becomes available.
1.3 Societal Impact
The BarrierPlus coatings technology developed in this project is expected to have a beneficial impact on the workforce of the European coatings industry. The majority of coatings in use today for structural steel applications are solvent-based, one-component or two-component systems. These coatings are typically applied to metal substrates by professional painting contractors, who are often SMEs. When these contractors apply solvent-based coatings, the chemical and physical hazards of these coatings products necessitate specialized training and the use of personal protective equipment, which may include eye protection, face protection, gloves, and possibly a respirator (when working in enclosed spaces or areas having poor ventilation). The low volatile emissions and use of water instead of solvents in the BarrierPlus coatings will significantly improve the working conditions for painting contractors. It reduces the burdens of personal protective equipment, saving money for SMEs and providing a safer work environment for painters. In addition, the low emissions and ease of water clean-up makes the BarrierPlus technology more accessible for use by non-professional, do-it-yourself type painters. This will enable the BarrierPlus technology to be used in a wider variety of applications, such as for residential and commercial architectural coatings.
Water-based coatings are generally easier to apply than solvent-based coatings. This may reduce the training requirements necessary to become a certified, professional painter, which would make the painting profession more accessible to a broader workforce.
A short term impact of BarrierPlus included the hiring of several post-doctoral and other professionals, who were employed by Surrey and UCBL to carry out research and administrative aspects of the project. The post-doctoral researchers gained valuable educational experience that they will leverage in their permanent employment positions in academia and industry.
2. Main Dissemination Activities
The Consortium disseminated results through a variety of means: publications in peer-reviewed journals, presentations at conferences and workshops, and publicly-available videos.
2.1. Publications in Peer-Reviewed Scientific Journals
To date, a total of six manuscripts have been written for publication in peer-reviewed scientific journals. Three of the manuscripts have now been published in international, high-impact journals: Physical Review Letters, Langmuir, and ACS Applied Materials and Interfaces (each published in the USA). Two manuscripts were submitted (Soft Matter and Steel Construction), and the final one is being revised for submission to Macromolecules. The publication in Physical Review Letters attracted international media attention (e.g. BBC News, The Independent Newspaper, The Daily Mail, etc.). One of the researchers, Andrea Fortini, was interviewed about the research on the BBC Surrey radio.
2.2. Presentations at Conferences, Expos and Workshops
At least 30 presentations were made at conferences, expositions and workshops by Consortium members. The audiences included researchers in both academia and in industry as well as users of coatings in a variety of fields. Two presentations of particular note are highlighted hereafter.
A highly successful lecture about the Barrier Plus technology was presented on May 26, 2016 at the European Technical Coatings Congress, which was held at the National Exhibition Centre in Birmingham, UK. The lecture was entitled “Advanced Water Borne Barrier Coatings for the Corrosion Protection of Structural Steel.” There was standing-room only in the lecture hall, with an estimated 130 delegates attending the presentation. Afterward, in the question session, there were several supportive and encouraging comments from the audience. The general feedback was that the concept of RAFT polymerization – with the organic/inorganic hybrids (UCBL research) when combined with the film formation results and analysis (Surrey research) was a great concept and not one attempted before. There were several comments looking forward to more results and paint information as generated during the balance of the project.
The Barrier Plus Project was represented at the Demolition, Decontamination and Recycling Expo held in Brussels from 14 to 16th June 2017. The potential of the project for reducing environmental impact was a strong attraction for potential partners from the Oil and Gas sector, whose offshore platforms will need refurbishment with minimal environmental impact. Mrs V. Dehan from the European Convention for Constructional Steelwork (ECCS) explained the potential of this new protection system, especially in harsh environments.
Professor Joe Keddie, from the University of Surrey, presented results from the Barrier Plus project at the Skandinaviska Lackteknikers Forbund (SLF) Congress in Gothenburg, Sweden in September 2015. His lecture reported insights into the stratification of waterborne coatings and the benefits of surfactant-free latex particles in increasing water barrier resistance of coatings. These results emerged from RTD performed by the teams at the Université Claude Bernard Lyon 1 (CNRS) and the University of Surrey as part of the Barrier Plus project.
His lecture was very well received by the 200 congress delegates, and his lecture was awarded a medallion from Coatings Societies International (CSI) for the Best Technical Paper. CSI is an association of international and national organisations devoted to the advancement of scientific and technical knowledge related to coatings, inks, construction materials and adhesives.
The SLF is the Federation of Scandinavian Paint and Varnish Technologists. It is the parent Nordic association for the four national associations from Denmark, Norway, Finland and Sweden.
The Coordinator of the Barrier Plus project, Professor Joe Keddie, presented the Thomas Graham Lecture at the UK Colloids 2017 Meeting in Manchester. In his lecture, he presented some of the discoveries made by the Surrey and Lyon teams working within the Barrier Plus project.
The Thomas Graham Lecture is awarded to those who are in the prime of their research careers, have established an international reputation in colloid science, have already made distinguished contributions to the field of colloid science, and have the prospect of a further 15+ years of active research to come. The lecture is named in honour of the 19th-century chemist who made major discoveries about the diffusion of gases and is considered one of the founders of colloid science. The lecturer is selected by the Joint Colloids Group of the Society of Chemical Industry (SCI) and the Royal Society of Chemistry (RSC).
UK Colloids 2017, which is described as an international colloids and interfacial science symposium, was held from July 10 to 12 at the Manchester Central Convention Centre.
2.3. Workshop on Surface Protection
A dedicated workshop was organised in Brussels on 12 April 2017 with the objective to gather together the market of steelwork and paint manufacturers (including resin manufacturers, polymers, powder coatings, etc.). The idea was to inform the profession about the existence of the Barrier Plus project and the potential commercial results, together with the advantages for the sector of steel construction, on the one hand, and for other sectors such as plastics, concrete, etc., allowing contacts between potential manufacturers for the future exploitation of technology.
The workshop was initiated and organised by ECCS-CECM. A key objective of the workshop was the creation of a Technical Committee on Surface Protection.
2.4. Videos and Websites
Two videos were created to explain coating self-stratification technology to a general audience. Both videos were published on YouTube and are available to be viewed on the project website at https://barrierplus.eu .
3 Exploitation of Results
Results will be exploited according to a defined plan, following consideration of patent searches, reviews of IP foreground, and execution of the IP strategy. All are described hereafter.
3.1 IP and Exploitation
Patent searches were performed in order to identify competitive patents that could inhibit progression of the BarrierPlus project, as well as, to seek opportunities for new intellectual property. Searches were limited to the European Patent Office (EP), World Intellectual Property Organization (WO), and U.S. granted patents published applications. The discovery of relevant patents was explored in technology areas related to BarrierPlus. The consortium monitored the specific coatings compositions assessed to meet the BarrierPlus objectives and will ensure IP is appropriately protected, as necessary. The IP protection needs of the BarrierPlus technology were assessed based on commercial coatings product benchmarks, both solventborne and waterbased, as well as an international patent study.
The BarrierPlus project contains a number of innovative approaches to the development of waterborne coatings for metallic surfaces and has generated significant intellectual know-how in the fields of surfactant-free self-cross-linking latex particles, polymer-encapsulated inorganic particles and Pickering stabilized lattices, as well as important know-how in the fields of barrier property models, formulation and testing. As part of the IPR management, patent searches were conducted by SME AGs and their partners to monitor for infringement of Foreground IP by third parties and/or potential conflicts with third parties’ IP. The project partners have the capability to supply the markets with BarrierPlus latex technology and coatings products. There is a strong core to market for the BarrierPlus technology.
3.2. Formation of a Technical Committee
Technical Committee 4 (Surface Protection) was set up by ECCS in order to further develop activities linked to the protection of steel structures through workshops, seminars, training courses, publication of guidelines and above all, drafting research projects.
Paint manufacturers, fabricators, and universities will be sitting on the Committee. One of the main and first missions will be to develop a follow-on research programme to extend the work of the Barrier Plus project. The objective will be to extend the positive characteristics of the BarrierPlus coatings (VOC free, REACH compliant, etc.) but raising to a protection level of 4 or 5, in order to be applicable in the fields of offshore oil structures and wind turbines.
List of Websites:
Project website: https://barrierplus.eu/
Project Co-ordinator: Professor Joseph Keddie (j.keddie@surrey.ac.uk)
This is the final report of the European Commission Framework 7 project entitled "BarrierPlus: One Component Waterborne Barrier Coatings."
Steel is the most used metal in construction and the costs of protecting Europe’s structural steel installations and assets from corrosion is thought to be 3% of GDP (or about €375BN). However, there are two factors that will increasingly affect future protective coatings developments: VOC emissions and health/safety issues. Firstly there is a strong mandate to apply VOC emissions legislation to protective coatings (and in particular extend the Paint Products Directive to include them). Secondly REACH, together with increasing effects of chemicals on humans supported through medical literature, may prevent the use of some coating additives and formulations.
Our vision for BARRIER-PLUS is to develop one-component waterborne barrier coatings that are competitive in performance to two component coatings. One component waterborne coatings have a number of advantages over two component coatings and solventborne systems: low VOC emissions; low fire risk; lower insurance issues; no exposure to isocyanates or epoxy resins; no waste or poor film performance arising from pot life problems. Our approach is to build upon recent research in the fields of polymers and organic/inorganic nanocomposites to create enhanced film barrier properties. Although this project is focused on the protection of steel, the technology developed will have applications in the protection of other substrates, e.g. concrete, brickwork and stonework.
The project has achieved its main objective. A one-component, water-based corrosion protective coating was developed for structural steel. The waterborne polymer used in the coating was manufactured without the use of conventional surfactants. This one-component system avoids the use of isocyanates, which are commonly used in two-component polyurethane coatings. Moreover, its VOC content is significantly lower compared to a solvent-borne coating. Clear and pigmented coatings were successfully applied to steel structures. A life cycle assessment confirmed that the environmental profile of the coatings is better than a solvent-borne benchmark coating. Further work will be required to optimize the BarrierPlus technology for potential commercialization.
Project Context and Objectives:
The main concept of the Barrier-Plus project is to develop a one-component waterborne barrier coating technology for the structural steel maintenance sector. Problems with existing barrier coatings include the emission of volatile organic compounds (VOCs), flammability, short pot-life and associated wastage, and the use of isocyanates which are harmful.
Our solution is to produce a one-component waterborne paint system by blending together self-stabilised acrylic latices elaborated within Work Package 1, and polymer-encapsulated inorganic latices or Pickering stabilised latices elaborated within Work Package 2. To make a barrier coating, these particles undergo a process of evaporation, particle packing, deformation, and coalescence. The polymer molecules in the particles were reacted to bond them together to make chemical crosslinks. The purpose of crosslinking is to increase the elastic modulus, increase the coating cohesion, and to add chemical resistance. The latices were formulated with various additives and pigments to make paints in Work Package 3. The manufacturing of the latices was scaled up to make larger volumes and to move the technology towards industrial production.
The steps in the film formation process were studied in Work Package 4. The arrangement of the particles in the coating was correlated with the barrier properties. Crosslinking was confirmed through studies of the mechanical properties. The formulated paints were applied to steel structures. The weathering of the paints was studied in outdoor exposure tests and in accelerated weathering tests. The final formulated paint achieved the project objectives of being a waterborne and one-component barrier coating. Stratified coatings containing inorganic particles can provide additional properties such as film hardness (e.g. from silica) and/or UV protection (e.g. from ceria).
Project Results:
Most of the existing coatings for structural steel have two key characteristics: (1) they are deposited by dissolving the polymer binder in an organic solvent (i.e. they are solvent borne); and (2) they are hardened or cured by mixing two components. Over 88% of the global protective coatings market is based on solvent-borne technologies. A good example is a two component (2K) solvent-borne acrylic polyurethane coating. In this system, one component is a polymer resin containing hydroxyl groups, which is dissolved in an organic solvent. Before the coating is applied to a metal surface, a second component consisting of isocyanate curing agents must be added to harden the coating.
Water-based coatings account for about 12% of the global protective coatings market, but only account for about 2% of the coatings used on steel. Waterborne coatings offer several advantages over their solvent-borne counterparts, namely (a) easier clean up, generally requiring only water and (b) reduced volatile organic compound (VOC) emissions. The latter reduces potential impacts on the environment and on human health, while meeting restrictions on emissions established by legislation. Additionally, waterborne coatings are not flammable, which ensures greater safety for manufacturing centres and workers.
Converting from a conventional 2K technology to a one component (1K) formulation offers additional benefits. The use of isocyanates and related curing chemicals is minimized or eliminated, thereby reducing chemical hazards. Additionally, there is reduced waste in 1K formulations. In 2K formulations, there is a short life of the product after it is mixed (“pot life”), whereas 1K formulations overcome this challenge and can have a longer pot life.
The FP7 BarrierPlus project aimed to develop 1K water-based anticorrosion coatings for structural steel with performance equal to conventional 2K solvent-borne coatings. The project’s consortium consisted of two European associations (European Convention for Constructional Steelwork, Belgium and Norsk Stålforbund, Norway), two SMEs (Megara Resins, Greece and Tuinsa Norte, Spain), an industrial partner (Sherwin-Williams Protective and Marine Coatings, UK) and three research centres (Université Claude Bernard Lyon 1, CPE Lyon, CNRS, France; University of Surrey, UK, and CREST, Dublin Institute of Technology, Republic of Ireland). This consortium worked together to prepare unique polymers, formulate coatings, and characterize and test these systems against industry standard benchmark solvent-borne and water-based coatings.
The binder for the coatings of the BarrierPlus technology initially consists of spherical polymer particles in water, in what is known as latex. These latex particles undergo a film formation process to form a binder for a coating. The particles, typically a few hundred nanometers in diameter, are stabilized in water. When the liquid is cast on a surface, such as by spraying, the water evaporates and particles pack together. Because of the effects of surface energy, the particles deform from their spherical shape to fill the space around them. The polymer molecules within the latex particles mix with the molecules in neighbouring particles, so that the particles fuse together (i.e. coalesce) to create a homogeneous solid barrier on the coated surface.
A major problem of the conventional waterborne binder technology is that the particles are stabilized by “water-loving” (or hydrophilic) molecules called surfactants. These hydrophilic soap-like molecules can be trapped at the boundaries of particles where they can create paths for water and salts to travel through a coating to corrode the underlying surface. The surfactants can also decorate the coating surface where they can decrease the gloss, cause tackiness, and encourage dirt pick-up.
The new technology developed in the BarrierPlus project does not rely on soap-like surfactant molecules in the binder. Instead the particles are stabilized with polymer molecules. Conventional waterborne binder particles are usually synthesized using emulsion polymerization in which the particles grow from clusters of the surfactant molecules. The surfactant covers the entire surface of the particles and offers stability in water. In contrast, the particles synthesized in the BarrierPlus project have spring-like polymer molecules on their surface.
1. Latex Synthesis
Organic latexes are most of the time stabilized by low molecular weight surfactants that sit at the surface of the final polymer particles. Several alternatives have been proposed to replace them or reduce their amount to counterbalance the negative impact of their migration once the film has been formed. Ionic or ionogenic comonomers, hydrophilic macromonomers, amphiphilic (block or random) copolymers have thus been used instead. In all cases, the hydrophilic component becomes strongly anchored at the particle surface (either via covalent bond or via hydrophobic interaction and/or entanglement). Due to their heterogeneous composition distribution, very large amounts of amphiphilic random copolymers are required and only a small percentage of the chains are really efficient in particle stabilization. For amphiphilic block copolymers, the main drawbacks are the multiple step synthesis and the need for a short hydrophobic block in order to allow an easy solubilization in water.
A new way of incorporating amphiphilic diblock copolymers with long hydrophobic block, without suffering from the aforementioned drawbacks (i.e. via a single preparation step, possibility of low amounts, no problem of solubility, no remaining water-soluble species if initiation is 100% efficient) is to start the polymerization with water-soluble chains that can be reactivated for the polymerization of a hydrophobic monomer. In situ quantitative chain extension in water in the presence of the core forming monomer(s) will afford an amphiphilic block copolymer - with possibility of high molecular weight for the hydrophobic block - that will self-assemble into micelles. Those micelles can be further used as a seed for conventional free-radical emulsion polymerization, toward high solids content latexes. Such re-activatable chains (also called living chains) are easily obtained by reversible-deactivation radical polymerization (RDRP). Among the available techniques, RAFT (reversible addition-fragmentation chain transfer) is very versatile and tolerant to many functionalities and reaction conditions, allowing the synthesis of these hydrophilic living chains (named macroRAFT) to be carried out in water. In this case, the overall process of latex synthesis can be conducted in a one-pot/two-step process starting from a hydrophilic monomer and feeding the hydrophobic monomer once the water-soluble macroRAFT is obtained. Carrying carboxylate, sulfate, sulfonate, phosphate, phosphonate monomer units or MPEGMAs (methoxypoly(ethylene glycol) methacrylates) those chains hence provide the final particles not only with stability but also additional properties.
1.1. Surfactant-free Latex (WP1)
UCBL employed a strategy to obtain surfactant-free latices that was inspired by the polymerization induced self-assembly (PISA) process performed in water. This is a “one pot” process in which the water-soluble macroRAFT (i.e. an hydrophilic polymer chain) carrying an end chain active in controlled radical polymerisation (CRP) (specifically, a thiocarbonylthio group) can be reactivated for the polymerization of hydrophobic monomers. The polymerization yields amphiphilic block copolymers that can act as in-situ formed stabilizers of the simultaneously forming latex particles. In the resulting self-stabilized latex particles, this macromolecular stabilizer is thus anchored and covalently linked to the particles. These stabilizing polymers are used instead of small molecule surfactants that are typically employed in conventional emulsion polymerization.
Initially, four model latices were synthesised via the copolymerization of n-butyl-acrylate (BA) and methyl methacrylate (MMA) (referred to in the project as latices A and B) or BA, MMA and styrene (S) (referred to as latices C and D), performed in the presence of poly(methacrylic acid) (PMAA) as the stabiliser. Additionally, a model latex obtained from the copolymerization of BA and in the presence of poly(sodium 4-styrene sulfonate) (PSSNa) as the stabiliser (called latex E) was also synthesised (as analogues of Latex A and B). The PSSNa macroRAFT stabilization seems to afford more stable latices compared to the PMAA-stabilized latices.
Each of these latices fit the requirements listed in the project specifications, most notably a solids (polymer) content of 40 wt% in water. They also contain less than 1.5 wt% of hydrophilic macroRAFT agent and less than 0.2 wt% of coagulum at the end of the polymerization. Some of the resulting polymers present broad glass transition temperatures (Tg). However, additional experiments showed that the use of a semi-batch process leads to a sharp glass transition region.
Starting from these four model latices, a crosslinking strategy was implemented to confer improved properties to the films formed from the latices. Three crosslinking strategies were employed and investigated. Strategy (1) leads to an internal crosslinking performed prior to the film formation while strategies (2) and (3) concern self-crosslinking reactions occurring during film formation.
A series of internally crosslinked latices were obtained via the introduction of 1,3-butanediol diacrylate (BuDA) as a co-monomer. However, because the particles were internally crosslinked, the interdiffusion of their constituent molecules was restricted. Furthermore, there was no crosslink formation between the particles within the film. Hence, weak and brittle films resulted. Consequently, this first strategy (1) was set aside and not investigated further.
The second strategy (2) used to obtain crosslinked films is based on the reaction between ketones (either diacetone acrylamide, DAAm, or acetoacetoxy ethylmethacrylate, AAEM) in the presence of reactive additives (a dihydrazide or a diamine) during film formation. Thus, both DAAm- and AAEM-functionalized latices based on the various original models have been synthesized and delivered. The final strategy (3) envisioned for the formation of crosslinked films relies on the introduction of a silane monomer during the emulsion polymerization. The functionalization of latices B and E using a silane co-monomer has been carried out and the samples sent to other partners for applications in coatings. The use of a semi-batch process resulted in polymers with well-defined and sharp glass transitions. The particle size was also decreased.
Concerning Strategy 2, tests on latices A-, B-, C- and D-type were carried out. Due to some opacity observed when forming films out of latex C, this one was set aside. Thus, different samples based on latex A, B and D were supplied to the other partners of the project. A new latex composition based on latex D, but stabilized with only 1.0 wt% of PMAA instead of 1.5 wt% was also developed and supplied. The objective was to reduce the amount of hydrophilic component.
For the AAEM/diamine strategy, latices stabilized with PMAA macroRAFT agent were delivered (A-, B- and D-type). A new latex containing more MMA than latex D (BA/S/MMA 55/10/35 wt% instead of 60/10/30 wt%) and less macroRAFT agent (1.2 wt% instead of 1.5 wt%) was developed.
1.2. Polymer-Encapsulated and Pickering Stabilised Latex Synthesis (WP2)
Hybrid latices based on the encapsulation of silica, ceria or titania have been synthesised. Silica (40-100 nm) encapsulated latices have been synthesised by a conventional route involving surface modification and surfactant stabilisation. This approach gives (single core)- shell hybrid latices with 20 wt.% solids content and particle sizes in the order of 100 nm. The final latices reach a limit around 30 wt% solids before significant coagulation is produced. Incidentally, a (multi core)-shell morphology due to particle coalescence is evident at a solids content close to the limit of instability.
The encapsulation of ceria and titania have been achieved through the use of macroRAFT-mediated emulsion polymerisation. Applying the same methodology to silica was unsuccessful due to poor interaction strengths between the macroRAFT agent and silica. The encapsulation of ceria (7 nm) has resulted in (multi core)-shell hybrid latices. Hybrid latices with particle sizes on the order of 500 nm have been synthesised. While targeting solids content greater than 30 wt.% results in high amounts of coagulation during synthesis, the formation of foam with samples containing 30 wt% solids content has further lowered the usable solids content to 20 wt.% for this system. Titania (400 nm) was encapsulated with a thin (15 nm) polymer shell surrounding individual titania particles, but large amounts of irreversible sedimentation was observed. Due to these instability problems, the model samples have been re-assessed to compromise the solids content for long-term stability. Long-term stability tests of the latices were introduced to guard against the problem.
Pickering-stabilised latices based on ceria and clay were also synthesised. Obtaining latices armoured with silica was less successful due to the poor interaction strengths between the polymer and silica. Hybrid latices using negatively charged ceria (7 nm) as a starting material allowed the formation of latices with up to 30 wt% solids content and large particles on the order of 800 nm. Due to the large size, the morphology cannot be ascertained. By using positively-charged ceria (7 nm), hybrid latices with an unquestionably armoured morphology were obtained with 30 wt.% solids content and particle sizes around 400 nm. However, instability was observed at pH > 7, which is problematic for paint formulations unless the charge on the particles can be inverted without irreversible aggregation. Latices armoured with clay platelets have also been synthesised with 20 wt.% solids content with 400 nm individual particles and some aggregation.
In general, hybrid latices with a minimum of 20 wt% solids content were obtained with most systems approaching instability at 30 wt% solids content. Pickering latices have reached 35 wt.% solids content (e.g. AC25) at which point a higher solids content produces high coagulation. As considered in the risk assessment, the use of lower than 40 wt% solids content is viable provided that the barrier property performance is good. To this end, samples AC12 (CeO2, encapsulation), AC19 (CeO2, Pickering), and MP-26 (clay, Pickering) were selected for further development as coatings.
All of the latices form films within the desired range of 0-25 °C allowing them to be studied for their barrier properties. All samples of encapsulated latices have sharp glass transition temperatures in the intended range for film formation at room temperature. Samples of Pickering latices have glass transitions that are significantly broader in temperature; nevertheless the minimum film-forming temperature experiments demonstrate film formation slightly below room temperature.
Ceria encapsulated, ceria Pickering latices, and clay Pickering latices were re-synthesised for film testing. In addition, internal and external crosslinking functionality were implemented. With concerns over the practicality and upscaling of synthesising encapsulated latices through a macroRAFT mediated strategy, as well as pressure to supply samples for the project work flow, subsequent work was concentrated on Pickering latices. Consequently, the number of Pickering latices supplied was greater than the target number, but the number of encapsulated latices supplied was approximately one-half of the target number.
The implementation of a semi-batch monomer feed gave more stable clay Pickering latices, which improved the films’ characteristics, such as transparency and texture. Implementing the semi-batch monomer feed, a range of samples were synthesised and characterised. Internal and external crosslinking functionality was also implemented.
A variation on the recipe of clay Pickering latices removed the auxiliary comonomer (PEGMA) and resulted in stable latices with a subtly different morphology (namely, smaller particle sizes and ‘less armoured’ per particle). By exploiting this variation, the size of the particles was fine tuned. Also, new information was obtained on the effect of the clay, auxiliary comonomer, and the morphology, on the film properties. This new approach also showed promise in reaching the targeted 40 wt% solids content. Solids content were increased to 35 wt%, although 30 wt% is recommended to avoid coagulum. For crosslinked films, gel fractions were increased using silane external crosslinkers. Various samples (including external crosslinking) were synthesised with solids content of 35 wt%.
While latices with 40 wt% solids content have not been achieved, mechanistic studies provide guidance towards further improvement. Mechanistic studies were performed on the synthesis of clay Pickering latices in order to increase solids content. Generally to obtain a stable latex, coalescence of particles should be minimised by exploiting the charge stabilisation of clay platelets. PEGMA reduces the effectiveness of clay as a stabiliser by screening charges. A slow monomer feed can allow time for the clay to reorganise and be more effective as well as reduce the number of monomer droplets which can interact with clay. Stirring also should be considered as it impacts particle collisions (and therefore coalescence), but a minimum speed is needed to aid monomer diffusion into the polymer particles.
It was found that various parameters can be tuned for a more fine control of the size of particles: by monomer composition in the case of ceria, and auxiliary comonomer and clay concentration in the case of clay.
Internal and external crosslinking have also been explored with various systems, but mostly clay Pickering latices due to the easier characterisation and ease of synthesis. 1,3- Butanediol diacrylate (BDA) and a functional silane monomer were effective at giving internally and externally crosslinked films, respectively. Gel fractions were calculated for all crosslinked Pickering latices, and was found to be particularly low for the silane-functionalised clay Pickering latices, which suggests that this system can be further improved.
Subsequently, self-crosslinking (MPTPS) ceria encapsulated latices were synthesised, based on the existing model samples to allow film comparisons to be made. Investigation of an inexpensive macroRAFT approach (use of PSSNa-CTPPA) to encapsulate ceria clusters using internal crosslinkers failed due to early aggregation. P(SSNa-stat-BA)-CTPPA macroRAFT agent was used to encapsulate ceria as a proof of concept and was successful, however this alternative approach can be optimised. Efforts to encapsulate clay through the use of PSSNa macroRAFT agents allowed us to obtain ‘dumbbell’ morphologies (i.e. clay platelets sandwiched by two polymeric nodes). Since the approach is less cost-effective than clay Pickering emulsion polymerisations and is limited to solid contents ≤ 20 wt%, benefits of this morphology requires justification.
To obtain a ‘true’ ceria Pickering latex which is stable in basic conditions, a different ceria source was used in conjunction with PSSNa-CTPPA to prevent clustering of ceria. Unfortunately, this idea was unsuccessful and the ceria lacked interaction with the polymer latex. Additional investigations were performed on blends of ceria, first to study the impact on a film between using a pre-assembled armoured structure compared to blends with ‘blank’ latices, then also as a means to introduce ceria to the polymer latex. More specifically, blends were made of ceria with macroRAFT-based latices from WP1, as well as blends of acidic sol Pickering latices with macroRAFT-based latices. While this route worked to an extent, the charge-inversion route with poly(acrylic acid) showed more promise towards ‘truly’ armoured ceria latices stable in basic conditions.
In summary, ten polymer-encapsulated latices have been synthesised and delivered as follows: four silica-encapsulated; one titania-encapsulated; and five ceria-encapsulated latices. A total of 23 ceria Pickering and 27 clay Pickering stabilized latices have been synthesized and delivered, including two crosslinked ceria Pickering samples and seven crosslinked clay Pickering samples.
2. Formulation
Throughout the formulation trials, several different additives were used for various purposes. The additives included a pigment dispersant, a defoamer, a surface tension modifier, flash corrosion inhibitor, a UV stabiliser, co-solvents, a rheology modifier, pigment, a corrosion inhibitor, an extender, and a filler.
A total of 70 formulations (clear and pigmented) were prepared, using the surfactant-free latex. Selected formulations were screened and evaluated using Electrochemical Impedance Spectroscopy, UV stability tests, and laboratory environmental corrosion tests.
After screening the various formulations, one clear and pigmented formulation was selected for scale-up for weathering testing. It was Latex A (JLH 268) with AAEM functional groups for crosslinking with HMDA.
The synthesis of six latexes were scaled-up to the laboratory (or pilot) scale at Megara and evaluated for formulation as both clear coats and pigmented coatings. These latexes are:
(1) Latex A + DAAM--JLH250
(2) Latex A + AAEM- JLH278
(3) Latex G + AAEM- JLH268
(4) Latex B + DAAM- JLH234/229
(5) Latex B + AAEM - JLH227
(6) Latex E + AAEM - JLH266
Thus, a total of twelve candidate coatings formulations were produced, which exceeds the eight formulations that were set as the original target. Three formulations were selected as being the most suitable for application testing. These final formulations required the addition of the HMDA cross-linker before outdoor weathering testing.
The stability of AAEM formulations containing the HMDA additive was studied. It was found that the BarrierPlus clear and pigmented formulations were indeed stable as a one-component formulation. Hence, the main objective of the project was achieved. This formulation was deemed to be suitable for C2 environments, which are exterior rural areas with low pollution, according to the ISO 12944 classification.
Issues observed included:
• Foaming during manufacture of clear or pigmented (and latex) which then dries to a very brittle film forming an insoluble crust, which breaks down easily.
• A tough hard settlement forms with the clear coats, which was not dispersed without high speed mixing, which can then induce undesirable foaming.
• A sharp drop in pH was observed with both JLH 268 and JLH 278 clear coats during a short storage period (5 days) at ambient temperatures. This sharp drop led to an irreversible particulate sediment forming in the delivered JLH 268 material.
• The JLH268 clear formulation is not stable at 5°C. Therefore it is not freeze/thaw stable and would suffer during winter storage.
• After five weeks of storage, the pigmented JLH278 was stable with a slight increase in viscosity at both 52°C and 5°C with no sedimentation observed.
Conclusions that can be drawn include:
• A further study of the clear formulations is required to develop a product with a sufficient shelf life that maintains a constant pH, which may be achieved using more suitable amine alternatives.
• The development of latexes requires more scale-up trial data through Megara Resins, which would be realistic of large-scale manufacturing conditions.
3. Film Formation and Properties of Latex Films
3.1. Experimental Studies of the Drying and Particle Packing in Particle Blends (WP4)
Experiments were conducted to understand the influence of different parameters (such as the presence, chemistry and amount of surfactant or macroRAFT agent in the latex synthesis, the size and number ratio in particle blends, and the annealing temperature) on the film formation process of coatings. Microscopies have been used as appropriate.
Film formation consists of three main processes: (1) water evaporation and particle packing; (2) particle deformation; (3) interdiffusion and coalescence. The introduction of macroRAFT agents in latices synthesized in WP1 were found to slow down the drying (water evaporation) process of coatings when compared with latexes made with surfactant or MAA stabilizer. Using a less hydrophilic macroRAFT (based on PSSNa) helps to reach the drying plateau faster than when using a more hydrophilic one (based on PMAA). The introduction of clay in the Pickering latex (5 and 10 wt.%) also slows down film formation when compared to a blank latex.
The difference in the barrier coatings made from surfactant-free particles is immediately apparent when examined at the sub-micrometre scale using an atomic force microscope. In a conventional waterborne coating, the surfactant was seen to accumulate in droplets on the film surface when aged at elevated temperatures. The surfactant-free coating made in the BarrierPlus project, on the other hand, has a more homogeneous surface structure and is more stable when aged.
Small angle neutron scattering (SANS) was used to follow in real time the last stages of film formation (coalescence and phase inversion) in macroRAFT (surfactant-free) and in surfactant-containing films. The data show a shift to lower wave-vector (q) along with a loss of peak intensity, which are changes attributed to the decrease in the particle spacing with water evaporation, followed by close-packing, and particle deformation. MacroRAFT samples annealed in the range of 100 to 200 °C show a distinct feature of 30-40 nm in size, which was also visualized via AFM images and identified as macroRAFT domains. This result shows that the macroRAFT agent does not form a continuous network throughout the coating when annealed. The water barrier properties of the coating might benefit from not having a continuous hydrophilic path from the top surface to the substrate. Surfactant, in comparison, formed blob-like structures on the films. This increased mobility surfactant compared with macroRAFT agents, and the rearrangement of surfactant into clusters, could be detrimental for water barrier properties.
Film formation studies in bimodal colloidal mixtures revealed a stratification effect. The smaller particles excluded the larger particles and formed a layer at the top of the drying film, as we demonstrated using AFM and confocal laser scanning microscopy. This newly-discovered mechanism will be useful whenever the properties of the top and the bottom of a coating need to be controlled independently via a one-step deposition process.
A binary colloidal system that allows self-stratification during drying can be "switched off" using pH as the trigger. Coatings are stratified when cast from dispersion with a pH below 7, but the effect is lost at higher pHs. The stimuli-responsive polymer colloids, synthesized in WP1, increase in size when the pH is raised. This switch off is explained by the combined effect of a decrease in the particle size ratio, an increase in the total volume fraction and a decrease in pressure gradients. Langevin dynamics simulations showed that when the particle size increases above 80 nm, the stratification is suppressed, which agrees remarkably well with the experiments. Achieving such control over the stratification process allows not only the independent programming of the properties of the top surface, but also the possibility of switching the surface properties without changing the starting materials.
3.2. Structure and Barrier Properties (WP4)
Experiments were conducted to understand the nano- and microstructures of the dry, film-formed waterborne coatings, and then to correlate the structures with barrier properties. Microscopies were used as appropriate. Additionally, water was used as a probe of structure via the characterisation of the states of water (dissolved, bound, freely-diffusing) within the coatings.
The characterization of surfactant-free latices synthesized in the presence of macroRAFT reveals that they show better barrier properties as measured by lower water sorption (from both liquid and vapour) and adhesion than control latices synthesized via standard emulsion polymerization using the same compositions. Comparison of the samples suggests that the amount of macroRAFT agent and its hydrophilicity are key parameters in the barrier properties of the coatings. The use of magnetic resonance relaxometry allowed the characterization of the distribution of water after soaking of the films, revealing that a less hydrophilic stabilizer leads to smaller water clusters. Atomic force microscopy was used to determine the structure of packed particles during coalescence. Water vapour sorption experiments show that the hydrophilic species are less accessible in macroRAFT latex films than in standard emulsion polymerization films of the same nominal composition.
The surfactant-free binder technology developed within the BarrierPlus project offers some obvious benefits in preventing the penetration of water through barrier coatings. When one of the surfactant-free 1K coatings, developed in the BarrierPlus project, is soaked in liquid water for one day, it absorbed approximately 17 wt% water, which shows it has poor suitability as a barrier coating. The stabilizing molecule on the particles in this formulation contains carboxylic acid (-COOH) groups in this example. However, when the stabilizing polymer molecule is substituted for another type of stabilizer without -COOH, only about 2 wt.% water is absorbed, after an initial uptake when first immersed in the water, which makes it more suitable for a barrier coating.
When a conventional waterborne (latex) coating is soaked in water for prolonged times, it becomes opaque because water penetrates the coating where it creates small droplets that scatter light. This phenomenon is referred to as “water whitening” in the coatings literature. The BarrierPlus coatings prevent water from penetrating, and they stay optically transparent even after soaking in water for up to three hours. The original latex composition displays evidence for water whitening, as the optical transparency decreases strongly over time. When a different stabilising polymer is used in the latex synthesis, there is very little water whitening. The superior properties of this BarrierPlus technology is apparent.
The 1K coatings technology developed within the BarrierPlus project uses particles that have chemical groups that react with molecules in the water phase (so-called crosslinkers) during the drying process. With added crosslinkers, the coating becomes harder, more scratch-resistant, and has improved barrier properties after curing.
Our studies show that the addition of cross-linking functionality to the latices can be either detrimental (if the latex particles are internally cross-linked) or beneficial (if the latex particles self-cross-link during film formation) for mechanical properties of the coatings and the retention of optical clarity. However, all of the cross-linking functionalization carried out within WP1 result in an increased amount of water sorbed upon soaking. External cross-linking of the macroRAFT latices via DAAm functionalization slows down water whitening considerably and improves the mechanical properties of the coating. However, the amount of water sorbed after 72h is higher than that of the blank. External cross-linking of the macroRAFT latices via AAEM functionalization does not improve significantly either the water barrier or the mechanical properties of the blank latex. Silane cross-linking slows down the water whitening process slightly and improves significantly the mechanical properties, except for the strain at failure which is reduced.
Our results show that the impact of the addition of ceria nanoparticles on the coating properties depends strongly on the ceria distribution within the coating. True armoured morphologies, such as obtained in the Pickering latex synthesized in WP2 using an acid ceria sol, where every latex particle is surrounded by ceria nanoparticles, show the best combination of high absorbance in the UV region and high visible transparency for coating applications. Also, the addition of ceria raises the storage modulus significantly at temperatures above Tg. However, when there is a significant amount of free ceria (such as in the Rhodigard ceria Pickering latices synthesized in WP2) there is a significant loss of transparency in the visible region. Optical properties were correlated with the structures determined using atomic force microscopy and electron microscopy. Moreover, the addition of ceria results in lower water content after soaking for 72h in comparison to the standard latex.
In Pickering clay nanocomposite films, the sorbed water is weakly bound, perhaps because of the nonpolar inorganic interfaces. Upon heating, the water is readily liberated. Latex films without clay particles retain water for temperatures as high as 200 °C. The 5 wt% clay samples (also the internally cross-linked latex) become opaque when soaked in water (i.e. “water whiten”) and then become transparent again with continuous soaking. This is a very unusual behaviour that could be related to a structural change.
3.3. Modelling of Film Formation
The modelling activity has been divided in three components: (1) Packing of mixtures of latex particles of different sizes; (2) calculation of the distribution of the length and diameters of the channels in the final film; and (3) deformation of the particles with viscoelastic flow.
3.3.1. Packing of mixtures of latex particles of different sizes
We studied coatings obtained from drying films containing mixtures of particles of different sizes. During evaporation the film’s air-water interface moves towards the bottom substrate. With computer simulations and theoretical modelling we have studied the drying process and the structure of the dry film. The initial study was carried out for two-component systems, i.e. a mixture of large and small model latex particles. We found that, when the number of small particles is larger than a critical value, the film stratifies into a layer of the larger particles at the bottom with a layer of the smaller particles on top. This is a potentially useful finding as stratified coatings could have novel properties, and will affect its barrier properties. The preponderance of small particles near the top of the film leads to smaller channels there and hence potentially better barrier properties to water ingress, of that part of the coating near the top surface. Hence, this finding was used as input into coatings studies at Surrey (with particles from Lyon), and these coatings studies verified our modelling predictions. The modelling predicted that if the particles were colloidally stable, that particle size was the dominant parameter, e.g. the effect would be found for conventional latices, surfactant-free latices, and those with and without inorganic material. This input informed particle synthesis at Lyon.
We developed a theoretical model to show that a gradient in osmotic pressure, which develops dynamically during drying, is responsible for the segregation mechanism behind stratification. The formation of stratified films was quite unexpected, therefore we investigated the formation of stratified layers in three-component systems, i.e. ternary mixtures of model latex particles of different sizes. The segregation mechanism was found to be important in ternary mixtures as well. The large parameter space available during formulation allows for a great control of the structure of the dry film. The modelling and simulation work on two-component systems reported here was published in Physical Review Letters in 2016.
The study of the packing of model latex particles in multicomponent systems was continued with studies of mixtures of polydisperse latex particles. The segregation mechanism was found here as well, but it has only a minor influence on the structure of the dry film.
3.3.2 Calculation of the distribution of channels in the film
A novel algorithm was developed to scan for empty spaces in the packings of dry films. The network of voids and channels was approximated by a collection of spheres. Cluster analysis was used to determine the structure of the network of channels. We found that the size of the largest voids is related to the size of the smallest particles. Furthermore, we found that the size and number of voids is larger nearer the substrate.
If small particles with attractive interactions are used in the composition, the resulting dry films have more voids and channels than dry films of purely repulsive particles. These attractive interactions model particles with reduced colloidal stability. Our models show that the size of the largest void, the number of voids, and the radius of gyration of the largest cluster of voids, i.e. biggest channel, are all smallest for particles with purely repulsive interactions. This is at the end of the packing of particles together caused by drying, but before coalescence. Thus for our mixed systems of particles, our modelling predicts that any attractions between the particles tend to create potentially problematic larger voids and channel. This suggests that barrier properties are optimised by minimising any attractions between the particles.
3.3.3 Deformation of particles with viscoelastic flows
The effect of particle deformation was investigated by discretising each latex particle into mobile
elements. These elements interact via an attractive interaction, and an elastic force. The dynamics of these elements, which leads to deformation of the particles, was modelled by a lattice dynamics. A ripening or coarsening of the voids driven by the minimisation of the surface free energy was found. The largest voids grow in size at the expense of the smallest voids. In perfectly ordered close-packed crystals, the coarsening leads to a reduction of the size of the network of channels connecting the top to the bottom of the film.
The deformation simulation was applied to the final particle packings found in our simulations of drying (which were far from perfect crystals). In these systems ripening leads to an increase in connectivity between different voids, leading to a percolated network of channels from the top surface of the film to the bottom substrate. The number of smaller voids was found to decrease during ripening. Also notable is that although introducing attractions between the particles, i.e. making the particles less colloidally stable, alters the pore structure before particle coalescence, the process of coalescence greatly reduces the difference attractions make to the final pore structure. This suggests that there should be a relatively large window of particle-particle interactions over which the final pore structure is invariant.
4. Weathering Testing
4.1 Application of Coatings
Prototype steel structures were coated and evaluated in terms of (1) Sag Resistance, (2) dry film thickness (DFT) and uniformity, and (3) Physical performance.
The performance of the Latexes JLH 278 and JLH 268 in pigmented and clear coatings was good in comparison to the commercial benchmarks. In particular, it was found that:
(a) Sag resistance was good with no running.
(b) The dry film thickness was controllable and within the expected range, while the coatings showed evidence of good edge coverage.
(c) The adhesion of JLH 278 (pigmented) was found to be good, achieving a rating of 1. JLH 278 (clear) adhesion was very good on direct-to-metal primer coatings and a 2K Epoxy (both rated 0) but poor on a JLH 278 coating (rating 5).
4.2 Corrosion Testing
The Barrier Plus samples with the JLH 278 pigmented base were all observed to corrode within the first cycle of D5894 testing without a scribe. The 2K Epoxy/JLH278 clear coatings developed corrosion spots following QUV accelerated weathering, but these didn’t degrade following cyclic corrosion tests. The JLH278 and JLH268 clear coatings on direct-to-metal primer samples maintained appearance with a small change in gloss. This is a promising result for the BarrierPlus materials.
In outdoor weather tests, the BarrierPlus pigmented and clearcoat coatings have so far performed favourably against the industrial benchmarks. Although weaker than the epoxy primed surfaces, the Barrier Plus systems are better than the Acrylic DTM systems in preliminary results. The outdoor weathering tests are ongoing.
4.3 Life Cycle Analysis
It was found through a life-cycle analysis that the BarrierPlus coatings had a lower environmental impact than benchmark solvent-based coatings. The commercial costs of the technology were investigated but cannot be determined until industrial-scale production is possible.
Potential Impact:
1. Impact
When a commercial product is developed from the BarrierPlus technology, it will have a number of competitive advantages over existing solvent-based and two-component systems:
- Lower health and safety risks;
- Reduction of maintenance times by improved barrier properties;
- Non-flammability;
- Lower VOC emission and compliance with REACH Legislation;
- Reduction of litigation risks in case of incorrect coating application.
The new coatings technology developed in the BarrierPlus project has the distinct potential to have economic, environmental, and societal impacts. Each type of impact is considered separately hereafter.
1.1. Economic Impact
The BarrierPlus technology, as developed in this programme, will primarily impact two commercial sectors, the structural steel sector (construction) and the protective coatings sector. There are likely also secondary project benefits that could impact the paint contractor industry and personal protective equipment sectors. But the focus here is on the overall effect likely to be achieved in the global protective coatings industry sectors intended for corrosion protection of large-scale, steel engineering structures. The global market segments affected are large in scope, and specifically in Europe, steel remains a key part of the European industry value chain with continuing yearly revenue streams in excess of € 3,000 billion, and employing 23 million people. All steel thus used must be protected from degradation and corrosion, and this is where the BarrierPlus technology can become impactful in the future. Recent market studies project that the global market size for such anti-corrosion coatings is estimated at € 18.4 billion, which is projected to grow to €26.5 billion by 2021 with a compound average growth rate (CAGR) of 5.1% between 2017 and 2021. From these projected values, products based on the BarrierPlus technology could well have a significant economic impact in the future, assuming the products thus developed function in ways that have commercial viability.
The coatings developed in the Barrier Plus project have potential to make an economic impact in the form of new products on the market. The market viability of any new product is always a function of the costs involved to produce, distribute and sell the product. In turn, these factors determine the eventual selling price for the product. All such cost factors must be manageable for a new product ultimately to be successful both in the European, and also in the global marketplaces. Manufacturing and supply chain cost analyses have been conducted. In this work, Megara Resins addressed the base resin manufacturing engineering and cost considerations of the BarrierPlus acrylic-latex materials. Market viability assessments for fully formulated paint products using the Megara-generated acrylic-latex resins were produced. Base resin manufacturing costs addressed in this analysis included variations needed in capital manufacturing machinery, as well as factory equipment adjustments needed for BarrierPlus technology differences when compared with more traditional manufacturing procedures for solvent-based paints and also for more traditional acrylic-latex manufacturing procedures.
In the BarrierPlus latex, the use of the macroRAFT agent increases costs in comparison with preparing the same latex with conventional free-radical polymerization and the appropriate emulsifier. An indicative assessment of costs for the macroRAFT latexes gave an estimated price that is significantly higher than a conventional industrial latex grade. MacroRAFT containing latexes have an estimated cost that is about 10 to 15 times higher than the cost of a conventional acrylic latex. This is due to the cost of the macroRAFT agent.The macroRAFT agent is a key chemical reagent necessary for the preparation of the surfactant-free latexes. MacroRAFT is not available as a commodity chemical. During the research phase of the BarrierPlus programme, UCBL were able to synthesize the chemical reagent (“RAFT agent”) for use at the research scale. 4-Cyano-4-thiothiopropylsulfanylpentanoic acid (CTPPA) was obtained by reaction of ACPA with bis(propylsulfanylthiocarbonyl) disulfide. However, much larger quantities are required for the scale-up for industrial manufacturing. Therefore, multiple quotations for pilot-scale quantities of RAFT agent were obtained and the lowest price option was selected for scale-up work. It should be emphasised that whilst the raw materials pricing considered in this report used the macroRAFT materials as purchased for this project, custom chemical manufacturing is significantly more expensive than eventual commodity production, the latter of which will likely be needed to achieve full commercial viability.
Differences in paint product formulating and manufacturing costs, as well as distribution and sales costs have also been addressed in order to evaluate the overall cost effectiveness expectations and likely final pricing of the BarrierPlus technology. Furthermore, the technology associated with BarrierPlus should add little if any complexity or cost to the eventual paint manufacturing and distribution business function, when the base acrylic latex paint ingredients are supplied for paint manufacturing.
The significantly higher cost of the macroRAFT-based latexes does not necessarily preclude BarrierPlus technology from market viability. If paints forumulated using BarrierPlus latexes exhibit paint performance properties for durabilty and corrosion protection that are equal to, or better than, the 2K solvent borne products that are in widespread use today, then there will be strong interest from the market for the new technology. Furthermore, in general, the cost of the paint resin (i.e. ‘binder’) which acts to hold together all the ingredients deemed necessary to make a successful paint, is typically the most expensive single formulation ingredient, and its cost can be mitigated somewhat by the use of necessary paint raw materials that are less expensive (e.g. use of low cost pigment extenders such as platy micas used to provide improved barrier properties to the paint so as to limit the ingress of water, oxygen, and corrosive species through the paint).
The original commercial objective of this project was to supply a one component waterborne barrier coating performing as well or better than a comparable two component system at a cost of no more than €10 per litre. The average anticipated costs for formulated pigmented and clear BarrierPlus coatings are reasonably in line with epoxy and polyurethane cost structures of typical products used today, thus meeting the project’s objective.
A further consideration is that the 1K BarrierPlus technology inherently results in a simpler paint technology option compared with today’s 2K solvent based epoxy and polyurethane options. The key difference is that the acrylic has only one component and does not require the complexity of a separate paint component for chemical curing processes.
Although final costings cannot be estimated at this time, the BarrierPlus technology will inevitably result in considerable overall job cost savings in terms of ease of paint application using simple brush, roll and airless spray equipment, rather than contractors having to mix components A and B, with the possible further need to use complex spray application equipment such as plural component equipment. With BarrierPlus technology, 1K products will have a longer potlife than today’s 2K solvent borne paints, which will also reduce unusable or waste paint, thereby reducing overall job costs.
In summary, although the BarrierPlus resin costs initially appear to be uncompetitively high, the overall cost considerations for broader commercial viability do not preclude use and consideration for future commercial exploitation.
The overall cost calculations and long term commercial viability for the BarrierPlus technology will ultimately be a function of the demonstrated product performance capabilities of the finished paints. In this respect, ongoing data produced in the BarrierPlus consortium program as described in Work Package 3 will likely be the determining factor for future technology success. If BarrierPlus technology can be shown to be superior to today’s solvent-borne products, then significant market penetration is likely in the future.
It should, however, be noted that the adoption of any new technology in this and other related structural steel markets must be tested and approved to industry standard specifications. Technology adoption rates for high performance paint requirements are expected to be slow initially. Initial years of commercialization would be limited to further testing and validation of coatings performance properties when exposed in real-world conditions. Nevertheless, expected coating sales values would still be substantial and of considerable benefit to society in general.
1.2. Environmental Impact
The coatings developed in the project have the potential to make an environmental impact. In a full Life-Cycle Assessment, BarrierPlus coatings system performed better than the solvent-based system and showed promising results relative to commercial waterborne benchmarks.
The bulk of the environmental impacts for each system were from the creation of the pigments and resins. The solvent system also had significant impacts due to the use of conventional solvents (as opposed to water). Typically, titanium dioxide was the single largest contributor across all impact categories for each product system. Transportation, packaging, disposal, and manufacturing were relatively minor contributors to overall impact. Application impacts were negligible unless the product contained a significant amount of VOC, which was then assumed to be emitted during the use phase (causing a spike in photochemical ozone creation during this phase).
In order to put the Life Cycle Impact Assessment (LCIA) results in context, the impacts for 4 m2 of steel plate was considered. The 4 m2 area selected is a conservative estimate of how much metal substrate would be covered by the coating systems given the functional unit of this study. This is to say that this value reflects expected coverage area from 1 kg of both the basecoat and the topcoat. Given that BarrierPlus and the coating benchmarks are designed to protect metal substrates, this metric showcases the importance of such coatings, as the metal substrate exhibited impacts around an order of magnitude higher across several key impact categories. The only indicators where the coating products were expected to have higher impacts were ozone depletion and smog formation. The latter of these is unsurprising given the VOC content of the coating products.
Given that BarrierPlus is only being made at a laboratory level scale, it was unsurprising that it had higher impacts than comparable water-based chemistries made through large-scale production channels. It is worth noting that some of the results were not statistically significant, especially toxicity. Taking this into account, BarrierPlus had an overall comparable environmental profile to the conventional water based benchmarks even if its impacts tended to run slightly higher than those benchmarks.
Interestingly, one of the primary impact drivers of BarrierPlus was the anti-corrosive pigment used in the formula. If this is able to be substituted to another raw material, BarrierPlus could reduce its impacts by 10-20% in certain impact categories. If this were to occur, BarrierPlus may become essentially equal in environmental impact to the water-based benchmark systems.
Toxicity in general is a problematic indicator given its high uncertainty. In addition, USETox was not able to take into account the fact that the surfactants found in several common resins were eliminated from the latex systems. Since no specific characterization factors for these chemicals currently exist in USETox, the models were not able to capture this distinct benefit.
Since no field study performance results were available for BarrierPlus at this time, it was assumed that all systems were performance-neutral. In reality, some of the systems may perform better or worse relative to BarrierPlus. A scenario was considered where BarrierPlus achieved 50% better performance than the benchmark systems.
High performance is key when considering overall environmental impact. If BarrierPlus was to have 50% better performance than the benchmarks, it performs equivalently or better in each indicator. This shows that any significant performance gain under the BarrierPlus product system leads to an overall environmental improvement. As such, care should be taken to ensure that the performance of BarrierPlus be as optimized as possible and the LCA models should be reassessed once actual performance data becomes available.
1.3 Societal Impact
The BarrierPlus coatings technology developed in this project is expected to have a beneficial impact on the workforce of the European coatings industry. The majority of coatings in use today for structural steel applications are solvent-based, one-component or two-component systems. These coatings are typically applied to metal substrates by professional painting contractors, who are often SMEs. When these contractors apply solvent-based coatings, the chemical and physical hazards of these coatings products necessitate specialized training and the use of personal protective equipment, which may include eye protection, face protection, gloves, and possibly a respirator (when working in enclosed spaces or areas having poor ventilation). The low volatile emissions and use of water instead of solvents in the BarrierPlus coatings will significantly improve the working conditions for painting contractors. It reduces the burdens of personal protective equipment, saving money for SMEs and providing a safer work environment for painters. In addition, the low emissions and ease of water clean-up makes the BarrierPlus technology more accessible for use by non-professional, do-it-yourself type painters. This will enable the BarrierPlus technology to be used in a wider variety of applications, such as for residential and commercial architectural coatings.
Water-based coatings are generally easier to apply than solvent-based coatings. This may reduce the training requirements necessary to become a certified, professional painter, which would make the painting profession more accessible to a broader workforce.
A short term impact of BarrierPlus included the hiring of several post-doctoral and other professionals, who were employed by Surrey and UCBL to carry out research and administrative aspects of the project. The post-doctoral researchers gained valuable educational experience that they will leverage in their permanent employment positions in academia and industry.
2. Main Dissemination Activities
The Consortium disseminated results through a variety of means: publications in peer-reviewed journals, presentations at conferences and workshops, and publicly-available videos.
2.1. Publications in Peer-Reviewed Scientific Journals
To date, a total of six manuscripts have been written for publication in peer-reviewed scientific journals. Three of the manuscripts have now been published in international, high-impact journals: Physical Review Letters, Langmuir, and ACS Applied Materials and Interfaces (each published in the USA). Two manuscripts were submitted (Soft Matter and Steel Construction), and the final one is being revised for submission to Macromolecules. The publication in Physical Review Letters attracted international media attention (e.g. BBC News, The Independent Newspaper, The Daily Mail, etc.). One of the researchers, Andrea Fortini, was interviewed about the research on the BBC Surrey radio.
2.2. Presentations at Conferences, Expos and Workshops
At least 30 presentations were made at conferences, expositions and workshops by Consortium members. The audiences included researchers in both academia and in industry as well as users of coatings in a variety of fields. Two presentations of particular note are highlighted hereafter.
A highly successful lecture about the Barrier Plus technology was presented on May 26, 2016 at the European Technical Coatings Congress, which was held at the National Exhibition Centre in Birmingham, UK. The lecture was entitled “Advanced Water Borne Barrier Coatings for the Corrosion Protection of Structural Steel.” There was standing-room only in the lecture hall, with an estimated 130 delegates attending the presentation. Afterward, in the question session, there were several supportive and encouraging comments from the audience. The general feedback was that the concept of RAFT polymerization – with the organic/inorganic hybrids (UCBL research) when combined with the film formation results and analysis (Surrey research) was a great concept and not one attempted before. There were several comments looking forward to more results and paint information as generated during the balance of the project.
The Barrier Plus Project was represented at the Demolition, Decontamination and Recycling Expo held in Brussels from 14 to 16th June 2017. The potential of the project for reducing environmental impact was a strong attraction for potential partners from the Oil and Gas sector, whose offshore platforms will need refurbishment with minimal environmental impact. Mrs V. Dehan from the European Convention for Constructional Steelwork (ECCS) explained the potential of this new protection system, especially in harsh environments.
Professor Joe Keddie, from the University of Surrey, presented results from the Barrier Plus project at the Skandinaviska Lackteknikers Forbund (SLF) Congress in Gothenburg, Sweden in September 2015. His lecture reported insights into the stratification of waterborne coatings and the benefits of surfactant-free latex particles in increasing water barrier resistance of coatings. These results emerged from RTD performed by the teams at the Université Claude Bernard Lyon 1 (CNRS) and the University of Surrey as part of the Barrier Plus project.
His lecture was very well received by the 200 congress delegates, and his lecture was awarded a medallion from Coatings Societies International (CSI) for the Best Technical Paper. CSI is an association of international and national organisations devoted to the advancement of scientific and technical knowledge related to coatings, inks, construction materials and adhesives.
The SLF is the Federation of Scandinavian Paint and Varnish Technologists. It is the parent Nordic association for the four national associations from Denmark, Norway, Finland and Sweden.
The Coordinator of the Barrier Plus project, Professor Joe Keddie, presented the Thomas Graham Lecture at the UK Colloids 2017 Meeting in Manchester. In his lecture, he presented some of the discoveries made by the Surrey and Lyon teams working within the Barrier Plus project.
The Thomas Graham Lecture is awarded to those who are in the prime of their research careers, have established an international reputation in colloid science, have already made distinguished contributions to the field of colloid science, and have the prospect of a further 15+ years of active research to come. The lecture is named in honour of the 19th-century chemist who made major discoveries about the diffusion of gases and is considered one of the founders of colloid science. The lecturer is selected by the Joint Colloids Group of the Society of Chemical Industry (SCI) and the Royal Society of Chemistry (RSC).
UK Colloids 2017, which is described as an international colloids and interfacial science symposium, was held from July 10 to 12 at the Manchester Central Convention Centre.
2.3. Workshop on Surface Protection
A dedicated workshop was organised in Brussels on 12 April 2017 with the objective to gather together the market of steelwork and paint manufacturers (including resin manufacturers, polymers, powder coatings, etc.). The idea was to inform the profession about the existence of the Barrier Plus project and the potential commercial results, together with the advantages for the sector of steel construction, on the one hand, and for other sectors such as plastics, concrete, etc., allowing contacts between potential manufacturers for the future exploitation of technology.
The workshop was initiated and organised by ECCS-CECM. A key objective of the workshop was the creation of a Technical Committee on Surface Protection.
2.4. Videos and Websites
Two videos were created to explain coating self-stratification technology to a general audience. Both videos were published on YouTube and are available to be viewed on the project website at https://barrierplus.eu .
3 Exploitation of Results
Results will be exploited according to a defined plan, following consideration of patent searches, reviews of IP foreground, and execution of the IP strategy. All are described hereafter.
3.1 IP and Exploitation
Patent searches were performed in order to identify competitive patents that could inhibit progression of the BarrierPlus project, as well as, to seek opportunities for new intellectual property. Searches were limited to the European Patent Office (EP), World Intellectual Property Organization (WO), and U.S. granted patents published applications. The discovery of relevant patents was explored in technology areas related to BarrierPlus. The consortium monitored the specific coatings compositions assessed to meet the BarrierPlus objectives and will ensure IP is appropriately protected, as necessary. The IP protection needs of the BarrierPlus technology were assessed based on commercial coatings product benchmarks, both solventborne and waterbased, as well as an international patent study.
The BarrierPlus project contains a number of innovative approaches to the development of waterborne coatings for metallic surfaces and has generated significant intellectual know-how in the fields of surfactant-free self-cross-linking latex particles, polymer-encapsulated inorganic particles and Pickering stabilized lattices, as well as important know-how in the fields of barrier property models, formulation and testing. As part of the IPR management, patent searches were conducted by SME AGs and their partners to monitor for infringement of Foreground IP by third parties and/or potential conflicts with third parties’ IP. The project partners have the capability to supply the markets with BarrierPlus latex technology and coatings products. There is a strong core to market for the BarrierPlus technology.
3.2. Formation of a Technical Committee
Technical Committee 4 (Surface Protection) was set up by ECCS in order to further develop activities linked to the protection of steel structures through workshops, seminars, training courses, publication of guidelines and above all, drafting research projects.
Paint manufacturers, fabricators, and universities will be sitting on the Committee. One of the main and first missions will be to develop a follow-on research programme to extend the work of the Barrier Plus project. The objective will be to extend the positive characteristics of the BarrierPlus coatings (VOC free, REACH compliant, etc.) but raising to a protection level of 4 or 5, in order to be applicable in the fields of offshore oil structures and wind turbines.
List of Websites:
Project website: https://barrierplus.eu/
Project Co-ordinator: Professor Joseph Keddie (j.keddie@surrey.ac.uk)