Final Report Summary - POLYGRAPH (Up-Scaled Production of Graphene Reinforced Thermosetting Polymers for Composite, Coating and Adhesive Applications)
Executive Summary:
The concept of the PolyGraph project was to develop new production techniques, which deliver industrial scale quantities of graphene-reinforced thermosetting polymers. This was achieved by developing new manufacturing routes starting from the relatively inexpensive expanded graphite starting material. Alongside this, we developed the equipment and techniques necessary to disperse the graphene into low-viscosity thermosetting polymer resins in a uniform, consistent and scalable basis. In addition, we optimised the techniques for the production of fibre-reinforced composites, adhesives and coatings, to ensure that the graphene remains well distributed in the final part.
PolyGraph was a four-year EC funded project coming to an end in October 2017 and made up of 14 partners across Europe: seven SMEs, four large companies, two universities and one research centre. Together we have developed a number of demonstrator parts to highlight the material developments we have made, along with LCA/LCC evaluations and a comprehensive study of the potential risks/hazards associated with the use of Graphene in thermosets.
PolyGraph has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 604143.
Project Context and Objectives:
Context
The concept of the PolyGraph project is to develop new production techniques which will deliver industrial-scale quantities of graphene-reinforced thermosetting polymers.
These materials will be suitable for use in a number of key applications where improvements are needed in the strength, stiffness, toughness, electrical conductivity, as well as thermal and barrier properties of polymers; such as fibre-reinforced composite resins, coatings and adhesives.
Interest in graphene and its potential uses has grown rapidly since 2004, when the material was first isolated using the now famous “Scotch tape” method by Professors Andre Geim and Konstantin Novoselov at the University of Manchester.
An area of particular significance is graphene-reinforced polymers. After several years of research in the area, it is now well known that the addition of small quantities of graphene can simultaneously provide significant improvements in strength, toughness, as well as electrical and thermal conductivity to a number of polymers. This has raised expectation levels with many industries, such as polymer composites, coatings and adhesives, which are keen to exploit the excellent properties of graphene in order to produce high performance polymer components. However it remains the case that there are no techniques suitable for industrial-scale production of graphene-reinforced polymers. Specifically, the following issues remain:
• Current graphene production processes are typically low yield, energy intensive, time consuming and often use large amounts of solvent.
• As a result, the cost of graphene remains prohibitively expensive for many industries.
• Incorporation and uniform distribution of graphene in low-viscosity thermosetting polymers has not yet been demonstrated on an industrial scale.
• Conventional composite, coating and adhesive processing techniques have not yet been optimised to ensure that graphene remains uniformly distributed during processing.
PolyGraph will address these issues by developing two new routes to industrial-scale quantities of graphene-reinforced thermosetting polymers; both starting from a relatively inexpensive expanded graphite starting material.
In the first route, we will develop new chemical and mechano-chemical methods to exfoliate the expanded graphite and produce graphene. Alongside this, we will develop the equipment and techniques necessary to disperse the graphene into low-viscosity thermosetting polymer resins in a uniform, consistent and scalable basis.
Our second route will go a step further and will develop the equipment and techniques to enable in-situ exfoliation of the expanded graphite and dispersion of the resulting graphene in a single operation, directly in the low-viscosity thermosetting polymer resins.
From here, we will optimise production methods to ensure that the graphene remains well dispersed during the production of fibre-reinforced composites, adhesives and coatings, so that the materials are ready for immediate up-take by industry.
To prove this new technology, we will produce demonstrator components from key target sectors such as aerospace and automotive.
These developments will lead to the utilisation of enhanced composites, adhesives and coatings within a number of industries where weight reduction, improved thermal and barrier performance and enhanced electrical properties are desired.
Main objectives
The ultimate aim of PolyGraph is to develop a process in which graphene can be produced and dispersed “in-situ” within thermosetting polymer resins, using relatively inexpensive expanded graphite as a starting material.
We propose a staged approach to reach this ambitious goal, starting with production of graphene via new chemical and mechano-chemical methods and its subsequent dispersion in thermosetting resins. We will then further develop and modify existing mixing and dispersion equipment to enable the exfoliation of expanded graphite to be carried out directly in thermosetting polymers.
A further aim is to optimise techniques for the production of fibre-reinforced composites, adhesives and coatings, to ensure that the graphene remains well distributed in the final part.
As a result, we will significantly lower the overall cost of these materials and make them viable for use in the wider composites, coatings and adhesives industries.
To achieve this, the following specific objectives have been set:
• Produce grades of specially designed graphite suitable for subsequent processing
• Use the new graphite to produce graphene via chemical and mechano-chemical methods
• Develop the equipment and processes to exfoliate and disperse graphene in thermosetting resins
• Utilise state of the art methods to monitor the dispersion process
• Develop, optimise and test the resin formulations for use in composites, adhesives and coatings
• Optimise fibre-reinforced composite, coating and adhesive production techniques such that the graphene remains well-dispersed during component production
• Scale-up of the novel equipment and production techniques
• Produce and test four demonstrator parts for key sectors (e.g. aerospace and automotive)
• Carry out health, environmental, and economic assessment in a life cycle context for the newly developed materials and processes
• Close the price-performance gap which currently exists for commercially available graphene
Project Results:
Work Package 1
The aim of the opening work package was to define the scope for subsequent development activities.
To begin with, a number of potential demonstrator parts were outlined; covering composite, coating and adhesive applications and spanning aerospace, marine and automotive sectors. The intention, at this early stage, was to provide sufficient detail so as to allow key performance criteria to be identified and approximate target performance values to be highlighted. These target performance values would then act as a reference point for the early project development work (until the final selection – and detailed specification – of demonstrator parts towards the latter stages of the project).
Having defined target performance, suitable base polymers were then chosen, taking into consideration factors such as chain length, functionality, viscosity, and cure characteristics. It was decided that a multi-stage approach would be used, whereby very simple resins would be used during initial “screening trials”, moving onto more complex (and realistic) resin systems later in the project.
Similarly, a range of graphite and graphene grades were outlined, taking into account the target technical performance (and therefore taking into account known size-property relationships, influence of functionalisation etc.) and anticipating the limitations which may be introduced by differing downstream processing techniques.
Finally, this work package identified the various exfoliation and dispersion techniques available within the consortium and provided an initial plan for their evaluation.
Work package 2
The main challenge of work package 2 was to scale-up of the production of graphite and graphene materials with innovative processes developed at laboratory stage. A large number of materials have been produced according to the various processing techniques present in the consortium. The large number of samples initially available by the consortium required extensive evaluation in later work packages. Only after a successfully selection of the grades, ranked according to the final properties of the relative composite material, was it possible to proceed with the effective up-scale that has been completely achieved both for the graphite and nanographite (from 1Kg to above 100Kg) and for graphene (above 25Kg). In parallel, the functionalization of some of the materials produced have been investigated. The main aim of functionalization is to increase the adhesion of the polymer resin to the graphene thus increasing the mechanical performance of the composite.
Work package 2 was organised according to the following tasks:
Task 2.1 – Initial Production of Novel Grades of Graphite
Task 2.2 – Initial Direct Production of Graphene in 50g Batches
Task 2.3 – Surface Functionalisation of Graphene and Expanded Graphite
Task 2.4 – Optimisation of Laboratory-scale Graphene and Functionalised Graphene Production
Task 2.5 – Graphite Production Scale-up
Task 2.6 – Graphene and Functionalised Graphene Production Scale-up to 25kg Batches
Task 2.1 was devoted to the production of graphite grades tailored for subsequent exfoliation in work package 3. Some of these graphites were produced by modifying existing industrial processes in large quantities in order to satisfy project needs. Large quantities already available at the beginning of the project allowed the partners to readily apply their strategies to produce graphene dispersions in work package 3. Some more innovative processes were also used during this task to produce new nanographites with better performance that were sent to work package 3 for further evaluation.
Task 2.2 was focused on graphene production and was organized in order to distinguish the different approaches to the production of graphene. IMERYS and QMUL aimed at reducing the thickness of the graphite platelet by mechanical force, trying to preserve the chemical composition of the graphene planes and avoiding oxidation while Avanzare concentrated on optimizing a combined mechanical and chemical treatment which they had previously developed. These initial trials were intended not only to optimizing existing processes but also to deliver innovative materials in quantities needed to be evaluated in the final composite application during work package 3. The main drawback of most of the graphene material on the market is the low quantity available. These materials are often sold in gram scale as they are still mainly produced at laboratory scale. With these small quantity most of the industrial trials are impossible to be carried out as they require more materials. The polymer industry tests are most often performed at the demonstrator stage and need large quantity of additives, also to demonstrate the repeatability of the process and its stability. Thanks to this project some of the materials produced in small scale (either graphene or nanographite) have been up-scaled to an intermediate phase (normally hundreds of grams). This intermediate scale was needed to properly evaluate them in work package 3 but also enabled some partners to use their technology to try to produce graphene using graphites (Netzsch, Ytron and QMUL).
As the effectiveness of a graphene material has to be evaluated in the final composite material, the several steps involved (production of graphene, dispersion, composite manufacturing and evaluation) slowed down the selection process and in general has been the main difficulty of the project. Only by a pragmatic down-selection between the many materials produced and evaluated (more than 50 samples) we were able to select the most interesting products (15 products) and start with their further up-scaling in the following tasks (Task 2.5 and 2.6).
The selection was carried out using final performance in the composite as the main criteria. Both electrical conductivity and mechanical properties were taken into account. It was found that graphene was the most conductive materials able to introduce electrical conductivity at extremely low loading (even lower than carbon nanotubes) while special graphite material with thickness higher than graphene is an interesting alternative to graphene having intermediate electrical properties between graphene and graphite. Mechanical and other properties have been evaluated in following work packages and during the project we keep on investigating higher thickness materials (referred to as expanded graphites and nanographites) together with graphene as judged by the consortium as potentially interesting from a performance and economical point of view.
During tasks 2.5 and 2.6 the up-scaling of some of the grades produced during tasks 2.1 and 2.2 took place. The selected grades that showed promising results were upscaled from hundred grams to the kilogram stage initially and successively, in some cases, to above 5Kg scale. Regarding products produced by modified industrial processes, tests were performing to provide the partners with the required quantities and also to test the repeatability and stability of the process. Regarding graphene production, by combining three lines together Avanzare was able to achieve more than 30Kg graphene production per batch achieving completely project target.
Special emphasis was devoted to the on line monitoring of the process parameters and the control of oxidation state of the graphene that is normally considered a key factor in graphene manufacture and performance. The performance of the graphene produced at large scale was compared with the same product produced in smaller scale and it was found that by upscaling the batch size, the material was more performant from an electrical conductivity point of view.
Finally, the work package investigated the functionalization of graphene (task 2.3 and task 2.4). This investigation was taken by many partners using different processes: Avanzare investigated mainly chemical routes by coupling agents, IMERYS investigated physical oxidation and reduction process and both Avanzare and IMERYS with the main contribution of SAIREM and University of Padova investigated functionalization by plasma. Avanzare investigated the functionalization of their graphene material by specific molecules by chemical bonding. They successfully demonstrated the functionalization by characterization and were able to demonstrate that the composite produced with their functionalized graphene increased electrical conductivity.
Oxidation and reduction was investigated by IMERYS but although effective change of the surface properties was achieved on the material powder, once cured in the resin, the functionalization showed no influence on most of the performance of the final composite material.
As plasma was known to be more effective and the preferential method for graphene functionalization, most of the efforts were devoted to this. Sairem produced a customized reactor for plasma functionalization and University of Padova worked on existing plasma generation devices with the reactor delivered by Sairem. They demonstrated that plasma treatment was effective in the functionalization of carbon based materials (both graphite and graphene) after having solved many initial problems (mainly related to the instability of the functionalization). Unfortunately, even though they were able to functionalize the two materials they did not observe any increase of mechanical or electrical properties in the expanded graphite product and only limited improvement of the mechanical properties (modulus) in the case of graphene. They found that the reason of this low performance is mainly attributed to the instability of the functionalization at the curing temperature. An alternative curing temperature could potentially overcome this problem, however this was outside the scope of this project.
Overall this work package was able to deliver the promised materials in the requested quantities. The main target, the up-scaling of expanded graphite, nanographite and graphene was fully accomplished (Avanzare was able to produce 30Kg/batch material) and the functionalization process (chemical or plasma process) was deeply investigated although the final answer on the impact of functionalization on the final composite performance has still to be fully clarified.
Work package 3
During the project the dispersion and exfoliation of a variety of graphite and graphene grades were tested using different mechanical and non-contact technologies. The exfoliating effect on graphite could be proven after processing of pre-mixed graphite/resin dispersions with the following three different methods: NETZSCH Dispersionizer, Triple Roll Mill and ultrasonic bath. Other tested technologies like rotor/stator homogenizers or micro-waving did not show significant exfoliation, while bead milling led to a reduction of the length and width of the platelets, which has a negative effect on the structural and electrical properties of the material in the final part.
Based on the positive results of the analyses of final part properties, a Graphite Exfoliation Plant was designed in two sizes. One for lab scale production of 10 kg graphene reinforced resin and one small industrial application with a capacity of 100 kg. Both plant designs consist mainly of an YTRON-Y Jet Mixer with powder addition tube and powder hopper installed in a heatable vacuum vessel for powder induction and pre-mixing of the initial graphite or graphene into the resin and of a NETZSCH Omega Dispersionizer for exfoliation and dispersion of the pre-mixed graphite filled resin.
In the Exfoliation Plant, the graphite powder is sucked in by the under pressure built up by mixing head of the Jet Mixer and directly mixed with the liquid below the surface to avoid dust emission of the powders of which some have an extremely low bulk density. The Jet Mixer produces a homogeneous graphite resin mixture which can be degassed after powder induction with the help of a vacuum pump. Then, the degassed resin is pumped to a NETZSCH Omega 60 or Omega 500 Dispersionizer for in-situ exfoliation of the wetted graphite by high pressure.
The OMEGA operation itself is easy and similar to all sizes of the machine. The total operating pressure is divided in to two settings. Nozzle and valve pressure. These pressures work together on the overall total pressure. Both parts have a different influence on the material itself. The nozzle will execute high shear and turbulence forces, elongation and cavitation on the material. The valve will execute impact forces to the material as the material impacts onto a wall. This combination offers the possibility to choose between the two of the different effects executed to the material.
After the exfoliation step the processed resin flows into a storage vessel from where it can be pumped either to a filling machine, to a mixing vessel for hardener addition or back into the inlet of the Dispersionizer again. Numerous trials showed that the most economic exfoliation result can be obtained by two passages through the Dispersionizer.
Process limitations due to the high viscosity of some filled resin formulations can be prevented by heating of the resin through the heat jacket of the vacuum vessel. This also shows a better results with the OMEGA when the material is slightly heated up.
The Exfoliation Plant is designed for operation in ATEX zone 1 and can be operated semi-automatic by a single person. The plant is compact as well and can be easily integrated into existing systems.
Work package 4
The aim of this work package is to take the graphene/graphite materials from WPs 2 & 3 and use them in the development of adhesive, coating and composite formulations.
The effect of addition of other additives (such as solvents, stabilisers, thixotropic additives or pigments) have been studied in order to ensure that dispersion of graphene is not adversely effected. This includes the following:
- Incorporate the graphene-reinforced polymer into an adhesive formulation
- Incorporate the graphene-reinforced polymer into a coating formulation
- Incorporate the graphene-reinforced polymer into a composite resin formulation
- Carry out analysis to determine the graphene dispersion levels and testing to evaluate performance
The concept has been to assess the range of improvements which were achieved through augmentation of the base composite, coatings or adhesives resins.
To aid the study and optimisation of the graphene formulations, it was decided to employ unmodified and well understood base thermosetting resins, free of any additional fillers (which may mask the effects of graphene). Additionally, it was important to employ two-part resin systems (i.e. resin and curing agent as separate parts) to afford greater options and flexibility for blending/dispersion studies.
The initial samples produced were based on a standard modified base epoxy resin with a reasonably short pot life and cure schedule. This enabled a screening matrix to be drawn up which shortlisted the best graphites, nano-graphites and graphene including few layer graphene. Hereafter called fillers.
The resultant viscosity increase vs % loading of filler was assessed and a selection of formulations were made and used for initial trials to measure dispersion using different equipment ranging from simple low shear hand mixing to high shear vacuum dispersers.
Once dispersed it is known that some fillers re-agglomerate and or sediment. This was evaluated by storage at elevated temperatures and monitored by use of microscopy. The use of surfactants and wetting agents has been evaluated. These were shown to make significant improvements.
The down selected list of fillers was incorporated into modified adhesive formulas and compared to standard proprietary resins commercially used in aerospace and automotive manufacture. The enhanced multifunctionality of the adhesives was demonstrated by measuring the adhesive lap shears and electrical conductivity on aluminium and GFRP substrates.
One key aim of the project was to take lower cost graphites and exfoliate in situ in a resin system. The resin allowed experimental work by the other partners to prove that triple roll mill (TRM) does in fact do that. Some of the other equipment designed would not process high viscosity mixes and the trials did not continue.
Another aim of the project was to show a method of dis-bonding the adhesive by use of RF or microwave. This was shown to work but the excessive smoke and fumes significantly limit the potential use.
The short useable pot life of the base resin proved to be limiting production of composite panels. To enable greater time for processing a hot curing system based on an aromatic curing agent was employed. Even with this longer application time it was not possible to produce resin transfer moulding (RTM) or vacuum infusion composites. This was primarily due to the filtration of the larger platelets particles. It was clearly demonstrated that there was a marked decrease in % filler loading vs distance from the injection point. The method chosen to overcome this was to use a pre-preg route to produce the composite. The resin formula was modified to enable the speed of crosslinking to be varied by addition of an accelerator. The correct addition level was determined using DSC and TMA instrumentation.
The final resin formulation enabled successful pre-preg to be produced with several fillers. The choice of filler was based on structural tests completed throughout the project.
The project effectively took standard epoxy and through careful formulation produced a number of working coupons and demonstrator parts.
Work package 5
The main aim of WP5 has been to further develop the adhesive, coating and composite formulations that were developed as part of WP4 and ensure the materials are optimised and suitable for product level manufacturing processes. The tasks include investigation into effects of end-user processing operations and optimisation of process parameters to achieve good quality and consistency.
In task 5.1 the end-users, plus formulators and science partners have worked in collaboration to evaluate and improve the suitability of the developing adhesives, coatings and composite matrices for deployment by the end-users under representative production environments, scales and processing equipment. In tasks 5.2 improvements, optimisations and innovative solutions have been considered to ensure the high levels of quality and reproducibility. Appropriate testing and analysis of the mechanical, electrical and morphological characteristics have been under concurrent evaluation as part of task 5.3. The main activities/findings are summarised below:
• Vacuum Assisted Resin Infusion and Resin Transfer Moulding techniques are popular for large scale and low cost manufacture of thermosetting composites. These techniques have been extensively investigated for fabrication of graphene/graphite fortified composites for both glass and carbon fibre laminates. It was noted that filtration induced segregation of the graphitic fillers was occurring to various degree of severity. Consequently, the filtration phenomenon was analysed comprehensively. It was demonstrated using different graphite and graphene with both glass fabric and carbon fabric. Experimental observation and associated theoretical models of the particle size limitation indicate that only graphite/graphene with small lateral dimensions can pass through the fabric. Therefore, the resin infusion processes are unsuitable for manufacture of composites with higher lateral size fillers which are in fact best suited for enhanced transport properties (e.g. electrical conductivity).
• Alternative composite processing techniques have been explored to overcome the filtration effects in cases where larger filler aspect ratios are desirable. These approaches aim to introduce the graphitic fillers close to their target destination within the laminate.
• A direct deposition technique has been developed to selectively add the graphene/graphite to composite interlaminar regions followed by resin infusion by conventional means. This has been shown to overcome the filtration effect and produce good quality laminates, but requires more development to achieve large scalability. Enabled functional properties include self-sensing effects for detection of strain and interlaminar damage as well as localised Joules heating of the laminate.
• The prepreg approach was also shown to be effective at overcoming the filtration issue. Both solvent based and holt-melt processing routes were investigated. The latter was successfully developed through modification of the base resin curing agent in order to promote partial Beta-stage cure of the resin and tailor its viscosity and tack as a prepreg matrix. A pilot prepreg line was designed and commissioned to enable sizeable production runs for the subsequent demonstrator activities.
• A range of graphene/graphite augmented structural adhesives were developed as part of the activities under WP4. In order to optimise the formulations for industrial applications they were analysed to down select the best formulations for further optimisation. A vacuum assisted mixing and cartridge filling technique was adopted to produce standard twin-pack dispensers suitable for use in industrial production settings.
Coatings developed in conjunction with WP4 were assessed for quality of finish, scalability and their functional effects to down select for scalable demonstrations under WP6. Electrical properties were suitable for protection provision of underlying composites against electromagnetic hazards (e.g. electromagnetic shielding and electrostatic discharge). Certain formulations were shown to provide strain sensing capabilities with good correlations between applied strain and resistivity change. Moisture barrier effects were characterised using accelerated conditioning in a high humidity chamber. Certain formulations were shown to provide a small but clear reduction in the moisture absorption content at saturation. Fire resistance behaviour of the coatings were characterised using the cone calorimetry technique. It was shown that certain formulations result in reduced heat release rate (HRR) peak intensities and associated reductions in the smoke production rates. A supplementary set of functional coatings were also developed (as part of WP6) to showcase enhanced functionalities, which included Joules heating for de-icing and synergistic fire protection properties.
Work package 6
Four demonstrator parts have been developed and tested, in order to assess PolyGraph materials technologies, in terms of:
✓ manufacturing scalability;
✓ structural performance;
✓ multi-functional properties.
The demonstrator parts, representative of automotive and aerospace applications, have been defined as follow:
• An aerospace structural element (adhesive demonstrator)
• A coated aerospace radome/fairing element (coating demonstrator)
• A composite material automotive rear seat back panel (composite demonstrator)
• An assembly of composite material automotive rear seat back panel, coated and bonded to a metal frame (combined demonstrator)
Such parts have been designed, produced, tested and benchmarked against similar parts with traditional technologies.
It must be emphasized that production processes suitable for industrial use have been chosen, such as prepreg compression moulding for the manufacturing of composite demonstrator part.
The compliance of PolyGraph materials technologies with the selected production processes has proven their manufacturing scalability.
Moreover, testing activities have shown satisfactory quality and multifunctional properties, consistent with the defined requirements, such as:
a) Structural behaviour;
b) Weight reduction;
c) Aesthetic quality;
d) Electrical properties;
e) Fire retardancy.
Main results are summarized as follows:
Adhesive demonstrator
• The manufacturing scalability and industrial applicability of graphene/graphite fortified adhesives pastes have been assessed.
• A strength improvement has been attained comparing the graphitic formulation with an unmodified baseline.
• The improved electrical conductivity will enable production of multifunctional bonded structures (e.g. for electromagnetic hazard protection).
• The adhesive systems were shown to be scalable and did not pose any significant issues with regard to processing, handling or quality of finish.
Coatings demonstrator
• The manufacturing scalability and industrial applicability of graphene/graphite fortified coatings have been assessed.
• The modified coatings were found to be highly scalable and produced good and uniform quality surface finish and adhesion. There was no significant processing, handling or application issues.
• A wide range of industrially exploitable multi-functional characteristics were demonstrated which include self-sensing, Electromagnetic Interference (EMI) shielding, fire protection and de-icing capabilities.
Composite demonstrator
• Assessed manufacturing feasibility with prepreg compression moulding process, suitable for upscaling to industrial production.
• Reached 25% weight reduction with respect to the reference steel panel.
• Assessed mechanical static performance for automotive requirements.
• Graphene loaded composite material shows increase in stiffness compared to unloaded composite material.
Combined demonstrator
• Assessed scalable manufacturing feasibility and integration of composites, adhesive and coating processes.
• Reached 22% weight reduction with respect to the reference steel part.
• Assessed mechanical static and impact performance for automotive requirements.
Work package 7
Work package 7 aimed to provide a holistic risk and life cycle assessment of the activities and products undertaken and developed throughout the course of the PolyGraph project. In order to achieve this specific tasks were undertaken, these incorporated:
• Support in defining the graphene and graphite grades to be developed
• Early identification of safety issues & risk management measures
• Screening level toxicity assessments
• Particle release and exposure measurement
• Risk management guidance
• Life cycle analysis of end products
Support in Defining the Graphene and Graphite Grades
Whilst the material manufacturers were focused on defining grades of graphene that had the desired properties (electrical, mechanical, thermal) for specific end applications, the aim of IOM was to help determine if there were size/shape parameters of platelet materials that were not conducive to efficient deposition in the lung i.e. were there possible combinations of lateral dimension and platelet thickness that could reduce lung deposition (and hence dose) for use in particle selection that is inherently, safer-by-design.
Using the general equation for the calculating the aerodynamic equivalent diameter of plate-like particles of given lateral size and thickness, deposition efficiency in the alveolar region was calculated using the Multiple-Path Particle Dosimetry (MPPD) model. The output was a table which plotted projected area diameter versus estimated aerodynamic diameter and percentage alveolar deposition for circular plate-like particles. Results demonstrated that for the majority of combinations, deposition in the alveolar region is relatively high irrespective of lateral dimension or thickness (e.g. particles with a lateral size of 100µm could potentially deposit with an efficiency of greater than 10%). It is only when both lateral dimension and thickness increase substantially that the percentage of alveolar deposition drops below 3% of total inhaled dose.
In general terms, based on the theoretical calculations, it was suggested that:
• if GFN are required to be very thin
• lateral dimension should be limited to <5µm
• above this size, they will not only deposit in the alveolar region with moderate efficiency but may cause some hindrance of normal clearance mechanisms.
It should be remembered however that the above suggestions are based on theoretical calculations and would need to be confirmed fully by detailed toxicological studies.
Early Identification of Safety Issues & Risk Management Measures
In order to gain early insight into the potential hazards and risks associated with the manufacture and use of graphene and graphene-containing materials, a detailed review of the published toxicology- and exposure-based literature was undertaken. Nanomaterial synthesis and functionalisation stages were identified as presenting the highest potential for particle release, mainly due to the manual handling of GFNs in powder form. The potential for particle release was considered to reduce as activities moved towards the manufacture of intermediates and end articles, as the GFNs become bound within the polymer matrix.
Initial sites identified for the particle release and exposure monitoring campaigns were those which handle GFN in bulk powder form.
The hazard review focused on identifying the hazard potential of GFN and GFN-containing products used within the scope of the project by conducting a review of published literature. Key findings from the literature identified that the plate-like structure and morphology of GFN caught the most interest of toxicologists, with a focus on the potential of large plate-like structures conferring low aerodynamic diameters resulting in deposition within the deep lung. The relationship between the aerodynamic and physical size of platelets, in combination with chemical properties, was therefore a focus for the in vitro study.
Screening Level Toxicity Assessment
The primary focus of in vitro studies was to assess the toxicological outcomes of the various GFN in relation to the physicochemical data in order to identify and validate structure activity relationships and/ or groupings of materials. Laboratory work was initially undertaken to characterise nine grades of GFN developed within the project.
As the lung is the main target of concern in relation to aerosol exposure, a bespoke system was developed to aerosolise bulk graphene powder in order to classify, characterise and isolate the respirable fraction of the test particles. The classification system allowed for in-situ characterisation of the aerosol generated from the respirable fraction, allowing the determination of the mass median aerodynamic size (MMAD) and confirmation that the material was in the respirable size range, whilst allowing sample collection for further offline analysis (e.g. in vitro toxicology, platelet sizing). Platelet sizing by scanning electron microscopy allowed samples to be characterised in terms of aerodynamic size and corresponding physical size. All nine GFN grades were seen to contain respirable platelets with lateral dimensions in excess of 10 µm.
The toxicity of PolyGraph materials was studied using in vitro testing with alveolar macrophages (resident cells within the lung and primary defender against deposited particles), bulk and respirable powders were assessed for
• Cytotoxicity
• Oxidative stress
• Pro-inflammatory effects
• Effects on cell migration
Cytotoxicity and oxidative stress analysis showed similar trends where, for many particles, the bulk fraction showed low toxicity whilst the respirable fraction showed much higher toxicity. The reason for this is not known (full mechanistic analysis would need to be undertaken), however particle size could be considered a possible explanation. The bulk phase contains a much more heterogeneous mix of particles including particles far too large for the macrophage to effectively engulf. This means that the cells may receive a lower internal dose than would occur when exposed to the same mass dose of smaller particles. Analysis of inflammation and migration identified the PolyGraph GFN to be relatively benign, with behaviour seen to be similar to that of low toxicity carbon particles. It is evident that further studies are required to study the relationship between the physico-chemical properties of GFN and their associated toxicological responses.
Particle Release and Exposure Assessment
Exposure monitoring was primarily conducted with partners who handled GFN products in bulk powder form. This incorporated seven site visits to investigate graphene manufacture, graphene functionalisation and preparation of dispersions and downstream processing of graphene-containing composites.
A substantial amount of instrumental and contextual data was collected during the exposure monitoring work program across the seven partner sites identified, involving a variety of activities, processes and tasks.
Whilst a significant amount of exposure and contextual data was gathered across the sites, common themes were identified and used to consolidate key findings. These cross-cutting themes consisted of information and advice relating to control measures, cleaning and waste disposal activities, elemental carbon sampling, aerodynamic size, persistence and material feed.
Whilst results were naturally variable across individual sites it was clear that those activities involving the handling and processing of GFN in powder form presented the highest risk of release and exposure. Analysis conducted during composite processing identified that release of GFN is not considered likely once the material has been dispersed within a polymer matrix.
With question marks remaining on the potential toxicity of GFN, combined with no current workplace exposure limits, it is recommended that effort be made to assess, control and prevent release and exposure to respirable GFN in the workplace.
Risk Management Guidance
Information gained from the extensive work carried out on hazard and exposure assessment was consolidated into a single risk management guidance document which aimed to provide industry-focused advice on the safe production and handling of graphene and graphene-containing polymers. The risk evaluation employed in the guidance document followed the general principles of a control banding approach, where specific controls are recommended based on process risk.
Using information from the hazard identification and exposure assessment, priorities and resources can be assigned to the management of these risks, commensurate with the level of risk.
To supplement this specific advice, a short summary of best practice guidance relating to the management of fume cupboards, local exhaust ventilation, personal protective equipment, respiratory protection, clean-up, and waste handling was also included in the guidance document.
Life Cycle Analysis
The objective of the LCA work was to understand whether the production of new graphene and related materials in polymers, either mixed into the polymer or exfoliated in situ, is more or less damaging to the environment than conventional materials and methods.
The LCA study identified that the service life of the demonstrator parts has the highest environmental impact by far. The coating and adhesive parts had lower overall impacts than their reference materials, but the composite and steel rear seat back panel had roughly equal overall impacts. Looking solely at the formulations, the additional material needed to meet the mechanical and electrical performance requirements of the adhesive increased the environmental impact of the reference formulation compared with the new PolyGraph formulation. The exfoliated material used in the coating formulation had the highest impacts in most categories due to the CO2 emissions when producing the starting material. When comparing the steel rear seat back panel to the composite, the steel has much less impact in all categories due to the lower level of material processing.
Work package 8
Dissemination
The main dissemination channels for the project have been the website (polygraphproject.eu) LinkedIn group and through attendance at events such as Graphene Week and INC (Industrial Nanocomposites Conference).
A range of marketing collateral was produced including flyers, posters, postcards, booklets, case study datasheets and videos. These were utilised at events, conferences and workshops to aid in the effective dissemination of the project.
Life Cycle Costing of End Products
The LCC analyses showed that the reference coating and adhesive formulations were slightly more expensive than the PolyGraph formulations due to the need for a carbon fibre veil to provide comparable electromagnetic interference performance. The composite formulations were much more expensive than the reference (steel) due to the costs of the materials and processing of the composite.
The lifecycle costs of the PolyGraph coating and adhesive demonstrator parts were less expensive than their heavier references due to the reduced weight of the PolyGraph parts. Weight reduction is an important factor in the transport industry; however, the magnitude of the results depends on the cost of fuel during the service life of the part.
The composite parts were slightly more expensive than the steel part (30 € vs. 25 €). The extra expense of the composite formulations was nearly balanced by the reduced production costs and fuel savings. An interesting feature of this comparison is that the steel part can be easily recycled, whereas the GFRP cannot be recycled at this time. Depending on the future recyclability of GFRP, and also on the value of the recycled materials, these results could change.
Potential Impact:
Work package 2
The consortium was able to identify the best performing materials according to their performance in thermosets. The relative processing routes have been implemented and optimized to deliver larger quantities (above 1kg) during the complete duration of the project and it permitted the realization of specific tests and evaluations that needed larger quantities of material, well above the few grams scale normally produced at R&D level. If any of the material developed in the successive work packages would be of industrial interest the project we would have the background information to start a continuous production or, if needed, increase further the production capacity. We found a basic agreement between conductivity and higher aspect ratio as most of the conductive model anticipated, but it is still not clear the advantages of lower loading would have in practice. The higher mechanical properties expected for graphene loaded compounds were not discovered. Mechanical properties are mainly linked to the surface state of the material that is determined by the specific processing that also determine the agglomeration state. Surface state requires long investigation and is difficult to control. As demonstrated during this project, although we could modify the surface state, the resulting higher mechanical properties were basically missing due to the instability of the functionalization to the curing temperatures. Overall, the performance of the material evaluated in composites is positive, but still far from the material performance hoped for. This difference is not able to justify mass commercial usage of most of the materials discovered due also to their high production costs. Following a general material development curve, the materials available are still in the development phase, but thanks to this project are available in larger quantities and ready for application development in many fields. This development work started in the applications within the scope of Polygraph project can continue further within the wider composite world. For example, one field of application not touched by the Polygraph project is lithium ion batteries but many other applications have still to be considered. By accelerating the application development, Europe will increase its competitiveness in the global arena being in a better position to achieve faster market introduction of graphene materials and being able to obtain better materials for better citizen lifestyle.
Work package 3
The newly designed prototype of a graphite exfoliation plant is capable of exfoliating most of the tested graphite grades at low and medium concentrations and is capable of dispersing some of graphene grades at low concentrations. The exfoliation plant can produce 100 kg batches of well dispersed graphene reinforced polymer within 3 hours. Since the powder addition during the pre-mixing step can be done below the liquid surface, the dust emission at the working place is minimized. As the pilot plant is a closed system with pipes, there will be very minimal solvent emissions, especially during the delamination process with the OMEGA machine. The pilot plant can be integrated in existing processes and follows ATEX regulations. The plant can be up- and downscaled as well, according to the needs.
Work package 4
Enhanced functionality has been demonstrated for the adhesive, coating and composite resin formulations.
Work package 5
Industrial utilization of composites, adhesives and coatings represent important and growing markets across diverse applications including aerospace, automotive, maritime and infrastructure. Successful augmentations with graphene/graphite promise to address some recognised deficiencies such as low electrical conductivities and poor matrix dominated composite properties. The WP5 outputs include a series of impactful and exploitable results:
• Resin infusion or resin transfer processing routes are attractive as relatively lower cost options, especially for larger components. Filtration effects, whereby the filler phase is gradually trapped and filtered out of the resin, have been studied and characterised in detail. There are significant filtration effects which are exacerbated through use of the larger flake sizes. The limit of the particle size constraints has been identified.
• Alternative composite processing techniques by means of direct dry fabric deposition and prepregging have been developed to successfully overcome the filtration effects for larger platelet sizes, which are of particular interest in formulations/applications that require improve transport properties.
• Wet lay-up, solvent based and hot-melt prepreg processing routes have been explored and assessed. The hot-melt technique was successfully adopted in a pilot line production facility. Working in collaboration with the resin supply partner, a suitable Beta-staged chemistry has been developed, implemented and demonstrated. This represents a notable advance in manufacturing readiness levels of graphitic composites.
• The direct deposition technique for manufacture of filtration-free laminates has demonstrated clear feasibility to deposit and localise GNPs into composite laminate. The capability has also enabled capabilities for composite strain-sensing and localised electrical heating. These functionalities can be exploited in the context of in-situ structural health monitoring and de-icing applications in high value composite structures.
• Disbond-on-command using graphitic structural adhesive developments showed feasibility of localised heating using microwave energy. Although bonded joint detachments were attained, further development is needed to optimise for more localised effects.
• Techniques for scalable and industrially applicable delivery of the adhesive formulations using vacuum mixing and dispensing using twin cartridges have been developed.
• Graphene/graphite augmented coating developments highlighted a number of exploitable functional properties. These include, protection against electromagnetic hazards (e.g. EMI or ESD); wide area strain sensing which could be used to promote structural health monitoring and condition based maintenance of high value structures; moisture barrier effects which may be deployed to reduce environmental degradation of composite structures; fire retardancy especially through development of synergistic effects; and utilisation of the electrical heating for de-icing of aerofoil structures. Importantly, a number of the functionalities can be integrated into a single coating solution.
Work package 6
On the basis of the achieved outcomes, several industrial applications may be developed, both in aerospace and in automotive sectors, such as:
• Lightweight structures, allowing lower fuel consumptions, emissions and operating costs
• New electrically conductive coatings, with de-icing and lightning strike protection functionalities and improved fire resistance
Moreover, the project activities and experience have contributed to the development of a specific and strategic knowledge, combined with the strong position Europe already enjoys in the composites, adhesives and coatings markets. This way the project has fostered the competitiveness of the European graphene production industry and also strengthened Europe’s position in the fields of advanced composites, specialty coatings and high-performance adhesives.
Possible industrialization of PolyGraph technologies will take advantage of the work carried out for production and testing of demonstrator parts, representative of high quality products, which can be translated into higher production volumes.
Work package 7
In order for any new technology to be successfully developed, adopted and sustained in a commercial sense, it must not only achieve the aspirational performance (and cost) targets but must also demonstrate that there are no underlying causes for concern with regards to potential health risks associated with either its manufacture or use. This is particularly relevant in the development of these novel advanced materials where regulation and specific knowledge on potential health concerns can significantly lag behind their fast-paced development.
This can be seen in the development of nanomaterials in general where, in the absence of meaningful toxicity assessment and more defined regulation, some organisations are seen to adopt a zero-use policy for these advanced materials. It is therefore clear that knowledge-based understanding of potential risks is integral in ensuring not only long-term sustainability but early adoption of these technologies.
From a health and safety perspective it is clear that the development in the understanding and knowledge of the potential impact of the aerodynamic properties of graphene (and nano-platelet materials in general) has identified a potentially significant risk which may negatively impact the development of graphene and graphene-containing materials. The work carried out in PolyGraph has significantly advanced our understanding in the potential risks associated with nano-platelets. This is particularly seen to be the case in the development of novel characterisation techniques that allow us to map aerodynamic and physical size of platelets whilst isolating the respirable fraction for more scientifically robust and meaningful in vitro toxicity assessments.
This understanding of aerodynamic properties transgresses potential toxicological behaviour into the workplace environment, where detailed exposure monitoring studies have highlighted the issue of particle persistence as a risk to organisations involved in either the manufacture or use of graphene in bulk powder form. Information and knowledge gained throughout the project has served to highlight these risks in order that appropriate steps can be undertaken to mitigate potential exposure to workers involved in these activities.
In contrast to the use of graphene in bulk powder form, detailed analysis has shown that risk of exposure is significantly reduced once the graphene is either in the dispersed phase (e.g. aqueous, solvent or resin systems) or in fully cured polymer matrices. Machining of graphene-containing composites has readily shown that the graphene remains embedded within the matrix and is not liberated as a free entity. Whilst there remains a lack of information on the toxicity of graphene-containing polymers (with regards to inhalation of respirable fragments generated through machining), it is considered to be the case that the toxicity should be consistent with that of the virgin polymer (based on analogous studies conducted with other nanomaterials, including carbon nanotubes). A caveat to this is that the graphene (nanomaterial) is adequately dispersed within the matrix i.e. there are no pockets of under-dispersed powder within the cured composite.
Whilst the health and safety work-package has significantly extended the knowledge on the potential risks associated with the manufacture and use of graphene and graphene-containing composites, it is clear that much work is still required in this relatively nascent area. This is particularly the case for the toxicology community where further, more in-depth, research is required to investigate further the potential toxicity of graphene (and 2D materials in general) with a specific focus in developing a correlation between toxicological response, mechanism of toxicity and physicochemical properties.
Work package 8
Dissemination
In September 2017, PolyGraph exhibited at Graphene Week. The 5-day event was attended by approximately 800 industry professionals. Several project partners provided talks at Graphene Week, along with a “Graphene Enhanced Composites” workshop held as a parallel session. On display on the exhibition stand was two demonstration parts and several samples made within the project.
The talks given at Graphene Week were:
• Preparation and processing of large lateral size graphene material in epoxy matrix composites - Julio Gomez Cordon, Avanzare, Spain
• Estimating the life cycle costs and environmental impacts of production of GRM and GRM filled polymer formulations - Francine Amon, RISE, Sweden
• Self-sensing using graphene in thermoset composites - Han Zhang, Queen Mary University of London, UK
In October 2017, PolyGraph will exhibit at the Industrial Nanocomposites Conference, where demonstration parts and samples will be on display. A talk will be given by one of the project partners.
A training video has been produced by IOM on health and safety aspects of working with graphene enhanced nanocomposites.
PolyGraph joined the Graphene Flagship as a partnering project, enabling cross-project dissemination of results with the aim of bringing together scientists, engineers and commercial companies looking to turn graphene and related materials from academic research into real-world products.
An initial press release, detailing the launch and objectives of the project was published within the first month of the project. The press release outlined the aims of the project and the project consortium members.
Further press releases were issued throughout the project to give updates on project progress and to notify people of the project’s attendance at various events.
Throughout the project various posters, flyers and postcards were produced which detailed the aims, objectives, development and outcomes of the project. The poster, flyer and postcard allowed partners to effectively dissemination the project’s broad goals.
During the later stages of the project some flyers and a booklet were produced giving details of the automotive and aerospace case studies.
PolyGraph project partners have attended many conferences, exhibitions and workshops throughout the duration of the project where its aims, objectives and outcomes have been disseminated.
Life Cycle Costing
The initially higher cost of GRM filled polymers may be a deterrent to their acceptance for use in commercial products (from a formulation manufacturing perspective); however, when the improvements in product performance and efficiency are considered (from a consumer perspective) it is possible to show that the GRM filled products are less expensive over the lifetime of the product. This is particularly true in the transport industry, where reduced weight is a very important factor in product design.
A challenge to the acceptance of composite replacements for steel parts, whether the composite is GRM filled or not, is the recyclability of the material at the end of life. Steel, although much heavier than composite, has recycling value. Future improvements in recycling technology might shift the balance more in favour of composite replacement parts.
Dr Gary Foster
Project Manager
NetComposites
4A Broom Business Park
Bridge Way
Chesterfield
S41 9QG
United Kingdom
Tel: +44(0)1246 266 244
Email: gary.foster@netcomposites.com
The concept of the PolyGraph project was to develop new production techniques, which deliver industrial scale quantities of graphene-reinforced thermosetting polymers. This was achieved by developing new manufacturing routes starting from the relatively inexpensive expanded graphite starting material. Alongside this, we developed the equipment and techniques necessary to disperse the graphene into low-viscosity thermosetting polymer resins in a uniform, consistent and scalable basis. In addition, we optimised the techniques for the production of fibre-reinforced composites, adhesives and coatings, to ensure that the graphene remains well distributed in the final part.
PolyGraph was a four-year EC funded project coming to an end in October 2017 and made up of 14 partners across Europe: seven SMEs, four large companies, two universities and one research centre. Together we have developed a number of demonstrator parts to highlight the material developments we have made, along with LCA/LCC evaluations and a comprehensive study of the potential risks/hazards associated with the use of Graphene in thermosets.
PolyGraph has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 604143.
Project Context and Objectives:
Context
The concept of the PolyGraph project is to develop new production techniques which will deliver industrial-scale quantities of graphene-reinforced thermosetting polymers.
These materials will be suitable for use in a number of key applications where improvements are needed in the strength, stiffness, toughness, electrical conductivity, as well as thermal and barrier properties of polymers; such as fibre-reinforced composite resins, coatings and adhesives.
Interest in graphene and its potential uses has grown rapidly since 2004, when the material was first isolated using the now famous “Scotch tape” method by Professors Andre Geim and Konstantin Novoselov at the University of Manchester.
An area of particular significance is graphene-reinforced polymers. After several years of research in the area, it is now well known that the addition of small quantities of graphene can simultaneously provide significant improvements in strength, toughness, as well as electrical and thermal conductivity to a number of polymers. This has raised expectation levels with many industries, such as polymer composites, coatings and adhesives, which are keen to exploit the excellent properties of graphene in order to produce high performance polymer components. However it remains the case that there are no techniques suitable for industrial-scale production of graphene-reinforced polymers. Specifically, the following issues remain:
• Current graphene production processes are typically low yield, energy intensive, time consuming and often use large amounts of solvent.
• As a result, the cost of graphene remains prohibitively expensive for many industries.
• Incorporation and uniform distribution of graphene in low-viscosity thermosetting polymers has not yet been demonstrated on an industrial scale.
• Conventional composite, coating and adhesive processing techniques have not yet been optimised to ensure that graphene remains uniformly distributed during processing.
PolyGraph will address these issues by developing two new routes to industrial-scale quantities of graphene-reinforced thermosetting polymers; both starting from a relatively inexpensive expanded graphite starting material.
In the first route, we will develop new chemical and mechano-chemical methods to exfoliate the expanded graphite and produce graphene. Alongside this, we will develop the equipment and techniques necessary to disperse the graphene into low-viscosity thermosetting polymer resins in a uniform, consistent and scalable basis.
Our second route will go a step further and will develop the equipment and techniques to enable in-situ exfoliation of the expanded graphite and dispersion of the resulting graphene in a single operation, directly in the low-viscosity thermosetting polymer resins.
From here, we will optimise production methods to ensure that the graphene remains well dispersed during the production of fibre-reinforced composites, adhesives and coatings, so that the materials are ready for immediate up-take by industry.
To prove this new technology, we will produce demonstrator components from key target sectors such as aerospace and automotive.
These developments will lead to the utilisation of enhanced composites, adhesives and coatings within a number of industries where weight reduction, improved thermal and barrier performance and enhanced electrical properties are desired.
Main objectives
The ultimate aim of PolyGraph is to develop a process in which graphene can be produced and dispersed “in-situ” within thermosetting polymer resins, using relatively inexpensive expanded graphite as a starting material.
We propose a staged approach to reach this ambitious goal, starting with production of graphene via new chemical and mechano-chemical methods and its subsequent dispersion in thermosetting resins. We will then further develop and modify existing mixing and dispersion equipment to enable the exfoliation of expanded graphite to be carried out directly in thermosetting polymers.
A further aim is to optimise techniques for the production of fibre-reinforced composites, adhesives and coatings, to ensure that the graphene remains well distributed in the final part.
As a result, we will significantly lower the overall cost of these materials and make them viable for use in the wider composites, coatings and adhesives industries.
To achieve this, the following specific objectives have been set:
• Produce grades of specially designed graphite suitable for subsequent processing
• Use the new graphite to produce graphene via chemical and mechano-chemical methods
• Develop the equipment and processes to exfoliate and disperse graphene in thermosetting resins
• Utilise state of the art methods to monitor the dispersion process
• Develop, optimise and test the resin formulations for use in composites, adhesives and coatings
• Optimise fibre-reinforced composite, coating and adhesive production techniques such that the graphene remains well-dispersed during component production
• Scale-up of the novel equipment and production techniques
• Produce and test four demonstrator parts for key sectors (e.g. aerospace and automotive)
• Carry out health, environmental, and economic assessment in a life cycle context for the newly developed materials and processes
• Close the price-performance gap which currently exists for commercially available graphene
Project Results:
Work Package 1
The aim of the opening work package was to define the scope for subsequent development activities.
To begin with, a number of potential demonstrator parts were outlined; covering composite, coating and adhesive applications and spanning aerospace, marine and automotive sectors. The intention, at this early stage, was to provide sufficient detail so as to allow key performance criteria to be identified and approximate target performance values to be highlighted. These target performance values would then act as a reference point for the early project development work (until the final selection – and detailed specification – of demonstrator parts towards the latter stages of the project).
Having defined target performance, suitable base polymers were then chosen, taking into consideration factors such as chain length, functionality, viscosity, and cure characteristics. It was decided that a multi-stage approach would be used, whereby very simple resins would be used during initial “screening trials”, moving onto more complex (and realistic) resin systems later in the project.
Similarly, a range of graphite and graphene grades were outlined, taking into account the target technical performance (and therefore taking into account known size-property relationships, influence of functionalisation etc.) and anticipating the limitations which may be introduced by differing downstream processing techniques.
Finally, this work package identified the various exfoliation and dispersion techniques available within the consortium and provided an initial plan for their evaluation.
Work package 2
The main challenge of work package 2 was to scale-up of the production of graphite and graphene materials with innovative processes developed at laboratory stage. A large number of materials have been produced according to the various processing techniques present in the consortium. The large number of samples initially available by the consortium required extensive evaluation in later work packages. Only after a successfully selection of the grades, ranked according to the final properties of the relative composite material, was it possible to proceed with the effective up-scale that has been completely achieved both for the graphite and nanographite (from 1Kg to above 100Kg) and for graphene (above 25Kg). In parallel, the functionalization of some of the materials produced have been investigated. The main aim of functionalization is to increase the adhesion of the polymer resin to the graphene thus increasing the mechanical performance of the composite.
Work package 2 was organised according to the following tasks:
Task 2.1 – Initial Production of Novel Grades of Graphite
Task 2.2 – Initial Direct Production of Graphene in 50g Batches
Task 2.3 – Surface Functionalisation of Graphene and Expanded Graphite
Task 2.4 – Optimisation of Laboratory-scale Graphene and Functionalised Graphene Production
Task 2.5 – Graphite Production Scale-up
Task 2.6 – Graphene and Functionalised Graphene Production Scale-up to 25kg Batches
Task 2.1 was devoted to the production of graphite grades tailored for subsequent exfoliation in work package 3. Some of these graphites were produced by modifying existing industrial processes in large quantities in order to satisfy project needs. Large quantities already available at the beginning of the project allowed the partners to readily apply their strategies to produce graphene dispersions in work package 3. Some more innovative processes were also used during this task to produce new nanographites with better performance that were sent to work package 3 for further evaluation.
Task 2.2 was focused on graphene production and was organized in order to distinguish the different approaches to the production of graphene. IMERYS and QMUL aimed at reducing the thickness of the graphite platelet by mechanical force, trying to preserve the chemical composition of the graphene planes and avoiding oxidation while Avanzare concentrated on optimizing a combined mechanical and chemical treatment which they had previously developed. These initial trials were intended not only to optimizing existing processes but also to deliver innovative materials in quantities needed to be evaluated in the final composite application during work package 3. The main drawback of most of the graphene material on the market is the low quantity available. These materials are often sold in gram scale as they are still mainly produced at laboratory scale. With these small quantity most of the industrial trials are impossible to be carried out as they require more materials. The polymer industry tests are most often performed at the demonstrator stage and need large quantity of additives, also to demonstrate the repeatability of the process and its stability. Thanks to this project some of the materials produced in small scale (either graphene or nanographite) have been up-scaled to an intermediate phase (normally hundreds of grams). This intermediate scale was needed to properly evaluate them in work package 3 but also enabled some partners to use their technology to try to produce graphene using graphites (Netzsch, Ytron and QMUL).
As the effectiveness of a graphene material has to be evaluated in the final composite material, the several steps involved (production of graphene, dispersion, composite manufacturing and evaluation) slowed down the selection process and in general has been the main difficulty of the project. Only by a pragmatic down-selection between the many materials produced and evaluated (more than 50 samples) we were able to select the most interesting products (15 products) and start with their further up-scaling in the following tasks (Task 2.5 and 2.6).
The selection was carried out using final performance in the composite as the main criteria. Both electrical conductivity and mechanical properties were taken into account. It was found that graphene was the most conductive materials able to introduce electrical conductivity at extremely low loading (even lower than carbon nanotubes) while special graphite material with thickness higher than graphene is an interesting alternative to graphene having intermediate electrical properties between graphene and graphite. Mechanical and other properties have been evaluated in following work packages and during the project we keep on investigating higher thickness materials (referred to as expanded graphites and nanographites) together with graphene as judged by the consortium as potentially interesting from a performance and economical point of view.
During tasks 2.5 and 2.6 the up-scaling of some of the grades produced during tasks 2.1 and 2.2 took place. The selected grades that showed promising results were upscaled from hundred grams to the kilogram stage initially and successively, in some cases, to above 5Kg scale. Regarding products produced by modified industrial processes, tests were performing to provide the partners with the required quantities and also to test the repeatability and stability of the process. Regarding graphene production, by combining three lines together Avanzare was able to achieve more than 30Kg graphene production per batch achieving completely project target.
Special emphasis was devoted to the on line monitoring of the process parameters and the control of oxidation state of the graphene that is normally considered a key factor in graphene manufacture and performance. The performance of the graphene produced at large scale was compared with the same product produced in smaller scale and it was found that by upscaling the batch size, the material was more performant from an electrical conductivity point of view.
Finally, the work package investigated the functionalization of graphene (task 2.3 and task 2.4). This investigation was taken by many partners using different processes: Avanzare investigated mainly chemical routes by coupling agents, IMERYS investigated physical oxidation and reduction process and both Avanzare and IMERYS with the main contribution of SAIREM and University of Padova investigated functionalization by plasma. Avanzare investigated the functionalization of their graphene material by specific molecules by chemical bonding. They successfully demonstrated the functionalization by characterization and were able to demonstrate that the composite produced with their functionalized graphene increased electrical conductivity.
Oxidation and reduction was investigated by IMERYS but although effective change of the surface properties was achieved on the material powder, once cured in the resin, the functionalization showed no influence on most of the performance of the final composite material.
As plasma was known to be more effective and the preferential method for graphene functionalization, most of the efforts were devoted to this. Sairem produced a customized reactor for plasma functionalization and University of Padova worked on existing plasma generation devices with the reactor delivered by Sairem. They demonstrated that plasma treatment was effective in the functionalization of carbon based materials (both graphite and graphene) after having solved many initial problems (mainly related to the instability of the functionalization). Unfortunately, even though they were able to functionalize the two materials they did not observe any increase of mechanical or electrical properties in the expanded graphite product and only limited improvement of the mechanical properties (modulus) in the case of graphene. They found that the reason of this low performance is mainly attributed to the instability of the functionalization at the curing temperature. An alternative curing temperature could potentially overcome this problem, however this was outside the scope of this project.
Overall this work package was able to deliver the promised materials in the requested quantities. The main target, the up-scaling of expanded graphite, nanographite and graphene was fully accomplished (Avanzare was able to produce 30Kg/batch material) and the functionalization process (chemical or plasma process) was deeply investigated although the final answer on the impact of functionalization on the final composite performance has still to be fully clarified.
Work package 3
During the project the dispersion and exfoliation of a variety of graphite and graphene grades were tested using different mechanical and non-contact technologies. The exfoliating effect on graphite could be proven after processing of pre-mixed graphite/resin dispersions with the following three different methods: NETZSCH Dispersionizer, Triple Roll Mill and ultrasonic bath. Other tested technologies like rotor/stator homogenizers or micro-waving did not show significant exfoliation, while bead milling led to a reduction of the length and width of the platelets, which has a negative effect on the structural and electrical properties of the material in the final part.
Based on the positive results of the analyses of final part properties, a Graphite Exfoliation Plant was designed in two sizes. One for lab scale production of 10 kg graphene reinforced resin and one small industrial application with a capacity of 100 kg. Both plant designs consist mainly of an YTRON-Y Jet Mixer with powder addition tube and powder hopper installed in a heatable vacuum vessel for powder induction and pre-mixing of the initial graphite or graphene into the resin and of a NETZSCH Omega Dispersionizer for exfoliation and dispersion of the pre-mixed graphite filled resin.
In the Exfoliation Plant, the graphite powder is sucked in by the under pressure built up by mixing head of the Jet Mixer and directly mixed with the liquid below the surface to avoid dust emission of the powders of which some have an extremely low bulk density. The Jet Mixer produces a homogeneous graphite resin mixture which can be degassed after powder induction with the help of a vacuum pump. Then, the degassed resin is pumped to a NETZSCH Omega 60 or Omega 500 Dispersionizer for in-situ exfoliation of the wetted graphite by high pressure.
The OMEGA operation itself is easy and similar to all sizes of the machine. The total operating pressure is divided in to two settings. Nozzle and valve pressure. These pressures work together on the overall total pressure. Both parts have a different influence on the material itself. The nozzle will execute high shear and turbulence forces, elongation and cavitation on the material. The valve will execute impact forces to the material as the material impacts onto a wall. This combination offers the possibility to choose between the two of the different effects executed to the material.
After the exfoliation step the processed resin flows into a storage vessel from where it can be pumped either to a filling machine, to a mixing vessel for hardener addition or back into the inlet of the Dispersionizer again. Numerous trials showed that the most economic exfoliation result can be obtained by two passages through the Dispersionizer.
Process limitations due to the high viscosity of some filled resin formulations can be prevented by heating of the resin through the heat jacket of the vacuum vessel. This also shows a better results with the OMEGA when the material is slightly heated up.
The Exfoliation Plant is designed for operation in ATEX zone 1 and can be operated semi-automatic by a single person. The plant is compact as well and can be easily integrated into existing systems.
Work package 4
The aim of this work package is to take the graphene/graphite materials from WPs 2 & 3 and use them in the development of adhesive, coating and composite formulations.
The effect of addition of other additives (such as solvents, stabilisers, thixotropic additives or pigments) have been studied in order to ensure that dispersion of graphene is not adversely effected. This includes the following:
- Incorporate the graphene-reinforced polymer into an adhesive formulation
- Incorporate the graphene-reinforced polymer into a coating formulation
- Incorporate the graphene-reinforced polymer into a composite resin formulation
- Carry out analysis to determine the graphene dispersion levels and testing to evaluate performance
The concept has been to assess the range of improvements which were achieved through augmentation of the base composite, coatings or adhesives resins.
To aid the study and optimisation of the graphene formulations, it was decided to employ unmodified and well understood base thermosetting resins, free of any additional fillers (which may mask the effects of graphene). Additionally, it was important to employ two-part resin systems (i.e. resin and curing agent as separate parts) to afford greater options and flexibility for blending/dispersion studies.
The initial samples produced were based on a standard modified base epoxy resin with a reasonably short pot life and cure schedule. This enabled a screening matrix to be drawn up which shortlisted the best graphites, nano-graphites and graphene including few layer graphene. Hereafter called fillers.
The resultant viscosity increase vs % loading of filler was assessed and a selection of formulations were made and used for initial trials to measure dispersion using different equipment ranging from simple low shear hand mixing to high shear vacuum dispersers.
Once dispersed it is known that some fillers re-agglomerate and or sediment. This was evaluated by storage at elevated temperatures and monitored by use of microscopy. The use of surfactants and wetting agents has been evaluated. These were shown to make significant improvements.
The down selected list of fillers was incorporated into modified adhesive formulas and compared to standard proprietary resins commercially used in aerospace and automotive manufacture. The enhanced multifunctionality of the adhesives was demonstrated by measuring the adhesive lap shears and electrical conductivity on aluminium and GFRP substrates.
One key aim of the project was to take lower cost graphites and exfoliate in situ in a resin system. The resin allowed experimental work by the other partners to prove that triple roll mill (TRM) does in fact do that. Some of the other equipment designed would not process high viscosity mixes and the trials did not continue.
Another aim of the project was to show a method of dis-bonding the adhesive by use of RF or microwave. This was shown to work but the excessive smoke and fumes significantly limit the potential use.
The short useable pot life of the base resin proved to be limiting production of composite panels. To enable greater time for processing a hot curing system based on an aromatic curing agent was employed. Even with this longer application time it was not possible to produce resin transfer moulding (RTM) or vacuum infusion composites. This was primarily due to the filtration of the larger platelets particles. It was clearly demonstrated that there was a marked decrease in % filler loading vs distance from the injection point. The method chosen to overcome this was to use a pre-preg route to produce the composite. The resin formula was modified to enable the speed of crosslinking to be varied by addition of an accelerator. The correct addition level was determined using DSC and TMA instrumentation.
The final resin formulation enabled successful pre-preg to be produced with several fillers. The choice of filler was based on structural tests completed throughout the project.
The project effectively took standard epoxy and through careful formulation produced a number of working coupons and demonstrator parts.
Work package 5
The main aim of WP5 has been to further develop the adhesive, coating and composite formulations that were developed as part of WP4 and ensure the materials are optimised and suitable for product level manufacturing processes. The tasks include investigation into effects of end-user processing operations and optimisation of process parameters to achieve good quality and consistency.
In task 5.1 the end-users, plus formulators and science partners have worked in collaboration to evaluate and improve the suitability of the developing adhesives, coatings and composite matrices for deployment by the end-users under representative production environments, scales and processing equipment. In tasks 5.2 improvements, optimisations and innovative solutions have been considered to ensure the high levels of quality and reproducibility. Appropriate testing and analysis of the mechanical, electrical and morphological characteristics have been under concurrent evaluation as part of task 5.3. The main activities/findings are summarised below:
• Vacuum Assisted Resin Infusion and Resin Transfer Moulding techniques are popular for large scale and low cost manufacture of thermosetting composites. These techniques have been extensively investigated for fabrication of graphene/graphite fortified composites for both glass and carbon fibre laminates. It was noted that filtration induced segregation of the graphitic fillers was occurring to various degree of severity. Consequently, the filtration phenomenon was analysed comprehensively. It was demonstrated using different graphite and graphene with both glass fabric and carbon fabric. Experimental observation and associated theoretical models of the particle size limitation indicate that only graphite/graphene with small lateral dimensions can pass through the fabric. Therefore, the resin infusion processes are unsuitable for manufacture of composites with higher lateral size fillers which are in fact best suited for enhanced transport properties (e.g. electrical conductivity).
• Alternative composite processing techniques have been explored to overcome the filtration effects in cases where larger filler aspect ratios are desirable. These approaches aim to introduce the graphitic fillers close to their target destination within the laminate.
• A direct deposition technique has been developed to selectively add the graphene/graphite to composite interlaminar regions followed by resin infusion by conventional means. This has been shown to overcome the filtration effect and produce good quality laminates, but requires more development to achieve large scalability. Enabled functional properties include self-sensing effects for detection of strain and interlaminar damage as well as localised Joules heating of the laminate.
• The prepreg approach was also shown to be effective at overcoming the filtration issue. Both solvent based and holt-melt processing routes were investigated. The latter was successfully developed through modification of the base resin curing agent in order to promote partial Beta-stage cure of the resin and tailor its viscosity and tack as a prepreg matrix. A pilot prepreg line was designed and commissioned to enable sizeable production runs for the subsequent demonstrator activities.
• A range of graphene/graphite augmented structural adhesives were developed as part of the activities under WP4. In order to optimise the formulations for industrial applications they were analysed to down select the best formulations for further optimisation. A vacuum assisted mixing and cartridge filling technique was adopted to produce standard twin-pack dispensers suitable for use in industrial production settings.
Coatings developed in conjunction with WP4 were assessed for quality of finish, scalability and their functional effects to down select for scalable demonstrations under WP6. Electrical properties were suitable for protection provision of underlying composites against electromagnetic hazards (e.g. electromagnetic shielding and electrostatic discharge). Certain formulations were shown to provide strain sensing capabilities with good correlations between applied strain and resistivity change. Moisture barrier effects were characterised using accelerated conditioning in a high humidity chamber. Certain formulations were shown to provide a small but clear reduction in the moisture absorption content at saturation. Fire resistance behaviour of the coatings were characterised using the cone calorimetry technique. It was shown that certain formulations result in reduced heat release rate (HRR) peak intensities and associated reductions in the smoke production rates. A supplementary set of functional coatings were also developed (as part of WP6) to showcase enhanced functionalities, which included Joules heating for de-icing and synergistic fire protection properties.
Work package 6
Four demonstrator parts have been developed and tested, in order to assess PolyGraph materials technologies, in terms of:
✓ manufacturing scalability;
✓ structural performance;
✓ multi-functional properties.
The demonstrator parts, representative of automotive and aerospace applications, have been defined as follow:
• An aerospace structural element (adhesive demonstrator)
• A coated aerospace radome/fairing element (coating demonstrator)
• A composite material automotive rear seat back panel (composite demonstrator)
• An assembly of composite material automotive rear seat back panel, coated and bonded to a metal frame (combined demonstrator)
Such parts have been designed, produced, tested and benchmarked against similar parts with traditional technologies.
It must be emphasized that production processes suitable for industrial use have been chosen, such as prepreg compression moulding for the manufacturing of composite demonstrator part.
The compliance of PolyGraph materials technologies with the selected production processes has proven their manufacturing scalability.
Moreover, testing activities have shown satisfactory quality and multifunctional properties, consistent with the defined requirements, such as:
a) Structural behaviour;
b) Weight reduction;
c) Aesthetic quality;
d) Electrical properties;
e) Fire retardancy.
Main results are summarized as follows:
Adhesive demonstrator
• The manufacturing scalability and industrial applicability of graphene/graphite fortified adhesives pastes have been assessed.
• A strength improvement has been attained comparing the graphitic formulation with an unmodified baseline.
• The improved electrical conductivity will enable production of multifunctional bonded structures (e.g. for electromagnetic hazard protection).
• The adhesive systems were shown to be scalable and did not pose any significant issues with regard to processing, handling or quality of finish.
Coatings demonstrator
• The manufacturing scalability and industrial applicability of graphene/graphite fortified coatings have been assessed.
• The modified coatings were found to be highly scalable and produced good and uniform quality surface finish and adhesion. There was no significant processing, handling or application issues.
• A wide range of industrially exploitable multi-functional characteristics were demonstrated which include self-sensing, Electromagnetic Interference (EMI) shielding, fire protection and de-icing capabilities.
Composite demonstrator
• Assessed manufacturing feasibility with prepreg compression moulding process, suitable for upscaling to industrial production.
• Reached 25% weight reduction with respect to the reference steel panel.
• Assessed mechanical static performance for automotive requirements.
• Graphene loaded composite material shows increase in stiffness compared to unloaded composite material.
Combined demonstrator
• Assessed scalable manufacturing feasibility and integration of composites, adhesive and coating processes.
• Reached 22% weight reduction with respect to the reference steel part.
• Assessed mechanical static and impact performance for automotive requirements.
Work package 7
Work package 7 aimed to provide a holistic risk and life cycle assessment of the activities and products undertaken and developed throughout the course of the PolyGraph project. In order to achieve this specific tasks were undertaken, these incorporated:
• Support in defining the graphene and graphite grades to be developed
• Early identification of safety issues & risk management measures
• Screening level toxicity assessments
• Particle release and exposure measurement
• Risk management guidance
• Life cycle analysis of end products
Support in Defining the Graphene and Graphite Grades
Whilst the material manufacturers were focused on defining grades of graphene that had the desired properties (electrical, mechanical, thermal) for specific end applications, the aim of IOM was to help determine if there were size/shape parameters of platelet materials that were not conducive to efficient deposition in the lung i.e. were there possible combinations of lateral dimension and platelet thickness that could reduce lung deposition (and hence dose) for use in particle selection that is inherently, safer-by-design.
Using the general equation for the calculating the aerodynamic equivalent diameter of plate-like particles of given lateral size and thickness, deposition efficiency in the alveolar region was calculated using the Multiple-Path Particle Dosimetry (MPPD) model. The output was a table which plotted projected area diameter versus estimated aerodynamic diameter and percentage alveolar deposition for circular plate-like particles. Results demonstrated that for the majority of combinations, deposition in the alveolar region is relatively high irrespective of lateral dimension or thickness (e.g. particles with a lateral size of 100µm could potentially deposit with an efficiency of greater than 10%). It is only when both lateral dimension and thickness increase substantially that the percentage of alveolar deposition drops below 3% of total inhaled dose.
In general terms, based on the theoretical calculations, it was suggested that:
• if GFN are required to be very thin
• lateral dimension should be limited to <5µm
• above this size, they will not only deposit in the alveolar region with moderate efficiency but may cause some hindrance of normal clearance mechanisms.
It should be remembered however that the above suggestions are based on theoretical calculations and would need to be confirmed fully by detailed toxicological studies.
Early Identification of Safety Issues & Risk Management Measures
In order to gain early insight into the potential hazards and risks associated with the manufacture and use of graphene and graphene-containing materials, a detailed review of the published toxicology- and exposure-based literature was undertaken. Nanomaterial synthesis and functionalisation stages were identified as presenting the highest potential for particle release, mainly due to the manual handling of GFNs in powder form. The potential for particle release was considered to reduce as activities moved towards the manufacture of intermediates and end articles, as the GFNs become bound within the polymer matrix.
Initial sites identified for the particle release and exposure monitoring campaigns were those which handle GFN in bulk powder form.
The hazard review focused on identifying the hazard potential of GFN and GFN-containing products used within the scope of the project by conducting a review of published literature. Key findings from the literature identified that the plate-like structure and morphology of GFN caught the most interest of toxicologists, with a focus on the potential of large plate-like structures conferring low aerodynamic diameters resulting in deposition within the deep lung. The relationship between the aerodynamic and physical size of platelets, in combination with chemical properties, was therefore a focus for the in vitro study.
Screening Level Toxicity Assessment
The primary focus of in vitro studies was to assess the toxicological outcomes of the various GFN in relation to the physicochemical data in order to identify and validate structure activity relationships and/ or groupings of materials. Laboratory work was initially undertaken to characterise nine grades of GFN developed within the project.
As the lung is the main target of concern in relation to aerosol exposure, a bespoke system was developed to aerosolise bulk graphene powder in order to classify, characterise and isolate the respirable fraction of the test particles. The classification system allowed for in-situ characterisation of the aerosol generated from the respirable fraction, allowing the determination of the mass median aerodynamic size (MMAD) and confirmation that the material was in the respirable size range, whilst allowing sample collection for further offline analysis (e.g. in vitro toxicology, platelet sizing). Platelet sizing by scanning electron microscopy allowed samples to be characterised in terms of aerodynamic size and corresponding physical size. All nine GFN grades were seen to contain respirable platelets with lateral dimensions in excess of 10 µm.
The toxicity of PolyGraph materials was studied using in vitro testing with alveolar macrophages (resident cells within the lung and primary defender against deposited particles), bulk and respirable powders were assessed for
• Cytotoxicity
• Oxidative stress
• Pro-inflammatory effects
• Effects on cell migration
Cytotoxicity and oxidative stress analysis showed similar trends where, for many particles, the bulk fraction showed low toxicity whilst the respirable fraction showed much higher toxicity. The reason for this is not known (full mechanistic analysis would need to be undertaken), however particle size could be considered a possible explanation. The bulk phase contains a much more heterogeneous mix of particles including particles far too large for the macrophage to effectively engulf. This means that the cells may receive a lower internal dose than would occur when exposed to the same mass dose of smaller particles. Analysis of inflammation and migration identified the PolyGraph GFN to be relatively benign, with behaviour seen to be similar to that of low toxicity carbon particles. It is evident that further studies are required to study the relationship between the physico-chemical properties of GFN and their associated toxicological responses.
Particle Release and Exposure Assessment
Exposure monitoring was primarily conducted with partners who handled GFN products in bulk powder form. This incorporated seven site visits to investigate graphene manufacture, graphene functionalisation and preparation of dispersions and downstream processing of graphene-containing composites.
A substantial amount of instrumental and contextual data was collected during the exposure monitoring work program across the seven partner sites identified, involving a variety of activities, processes and tasks.
Whilst a significant amount of exposure and contextual data was gathered across the sites, common themes were identified and used to consolidate key findings. These cross-cutting themes consisted of information and advice relating to control measures, cleaning and waste disposal activities, elemental carbon sampling, aerodynamic size, persistence and material feed.
Whilst results were naturally variable across individual sites it was clear that those activities involving the handling and processing of GFN in powder form presented the highest risk of release and exposure. Analysis conducted during composite processing identified that release of GFN is not considered likely once the material has been dispersed within a polymer matrix.
With question marks remaining on the potential toxicity of GFN, combined with no current workplace exposure limits, it is recommended that effort be made to assess, control and prevent release and exposure to respirable GFN in the workplace.
Risk Management Guidance
Information gained from the extensive work carried out on hazard and exposure assessment was consolidated into a single risk management guidance document which aimed to provide industry-focused advice on the safe production and handling of graphene and graphene-containing polymers. The risk evaluation employed in the guidance document followed the general principles of a control banding approach, where specific controls are recommended based on process risk.
Using information from the hazard identification and exposure assessment, priorities and resources can be assigned to the management of these risks, commensurate with the level of risk.
To supplement this specific advice, a short summary of best practice guidance relating to the management of fume cupboards, local exhaust ventilation, personal protective equipment, respiratory protection, clean-up, and waste handling was also included in the guidance document.
Life Cycle Analysis
The objective of the LCA work was to understand whether the production of new graphene and related materials in polymers, either mixed into the polymer or exfoliated in situ, is more or less damaging to the environment than conventional materials and methods.
The LCA study identified that the service life of the demonstrator parts has the highest environmental impact by far. The coating and adhesive parts had lower overall impacts than their reference materials, but the composite and steel rear seat back panel had roughly equal overall impacts. Looking solely at the formulations, the additional material needed to meet the mechanical and electrical performance requirements of the adhesive increased the environmental impact of the reference formulation compared with the new PolyGraph formulation. The exfoliated material used in the coating formulation had the highest impacts in most categories due to the CO2 emissions when producing the starting material. When comparing the steel rear seat back panel to the composite, the steel has much less impact in all categories due to the lower level of material processing.
Work package 8
Dissemination
The main dissemination channels for the project have been the website (polygraphproject.eu) LinkedIn group and through attendance at events such as Graphene Week and INC (Industrial Nanocomposites Conference).
A range of marketing collateral was produced including flyers, posters, postcards, booklets, case study datasheets and videos. These were utilised at events, conferences and workshops to aid in the effective dissemination of the project.
Life Cycle Costing of End Products
The LCC analyses showed that the reference coating and adhesive formulations were slightly more expensive than the PolyGraph formulations due to the need for a carbon fibre veil to provide comparable electromagnetic interference performance. The composite formulations were much more expensive than the reference (steel) due to the costs of the materials and processing of the composite.
The lifecycle costs of the PolyGraph coating and adhesive demonstrator parts were less expensive than their heavier references due to the reduced weight of the PolyGraph parts. Weight reduction is an important factor in the transport industry; however, the magnitude of the results depends on the cost of fuel during the service life of the part.
The composite parts were slightly more expensive than the steel part (30 € vs. 25 €). The extra expense of the composite formulations was nearly balanced by the reduced production costs and fuel savings. An interesting feature of this comparison is that the steel part can be easily recycled, whereas the GFRP cannot be recycled at this time. Depending on the future recyclability of GFRP, and also on the value of the recycled materials, these results could change.
Potential Impact:
Work package 2
The consortium was able to identify the best performing materials according to their performance in thermosets. The relative processing routes have been implemented and optimized to deliver larger quantities (above 1kg) during the complete duration of the project and it permitted the realization of specific tests and evaluations that needed larger quantities of material, well above the few grams scale normally produced at R&D level. If any of the material developed in the successive work packages would be of industrial interest the project we would have the background information to start a continuous production or, if needed, increase further the production capacity. We found a basic agreement between conductivity and higher aspect ratio as most of the conductive model anticipated, but it is still not clear the advantages of lower loading would have in practice. The higher mechanical properties expected for graphene loaded compounds were not discovered. Mechanical properties are mainly linked to the surface state of the material that is determined by the specific processing that also determine the agglomeration state. Surface state requires long investigation and is difficult to control. As demonstrated during this project, although we could modify the surface state, the resulting higher mechanical properties were basically missing due to the instability of the functionalization to the curing temperatures. Overall, the performance of the material evaluated in composites is positive, but still far from the material performance hoped for. This difference is not able to justify mass commercial usage of most of the materials discovered due also to their high production costs. Following a general material development curve, the materials available are still in the development phase, but thanks to this project are available in larger quantities and ready for application development in many fields. This development work started in the applications within the scope of Polygraph project can continue further within the wider composite world. For example, one field of application not touched by the Polygraph project is lithium ion batteries but many other applications have still to be considered. By accelerating the application development, Europe will increase its competitiveness in the global arena being in a better position to achieve faster market introduction of graphene materials and being able to obtain better materials for better citizen lifestyle.
Work package 3
The newly designed prototype of a graphite exfoliation plant is capable of exfoliating most of the tested graphite grades at low and medium concentrations and is capable of dispersing some of graphene grades at low concentrations. The exfoliation plant can produce 100 kg batches of well dispersed graphene reinforced polymer within 3 hours. Since the powder addition during the pre-mixing step can be done below the liquid surface, the dust emission at the working place is minimized. As the pilot plant is a closed system with pipes, there will be very minimal solvent emissions, especially during the delamination process with the OMEGA machine. The pilot plant can be integrated in existing processes and follows ATEX regulations. The plant can be up- and downscaled as well, according to the needs.
Work package 4
Enhanced functionality has been demonstrated for the adhesive, coating and composite resin formulations.
Work package 5
Industrial utilization of composites, adhesives and coatings represent important and growing markets across diverse applications including aerospace, automotive, maritime and infrastructure. Successful augmentations with graphene/graphite promise to address some recognised deficiencies such as low electrical conductivities and poor matrix dominated composite properties. The WP5 outputs include a series of impactful and exploitable results:
• Resin infusion or resin transfer processing routes are attractive as relatively lower cost options, especially for larger components. Filtration effects, whereby the filler phase is gradually trapped and filtered out of the resin, have been studied and characterised in detail. There are significant filtration effects which are exacerbated through use of the larger flake sizes. The limit of the particle size constraints has been identified.
• Alternative composite processing techniques by means of direct dry fabric deposition and prepregging have been developed to successfully overcome the filtration effects for larger platelet sizes, which are of particular interest in formulations/applications that require improve transport properties.
• Wet lay-up, solvent based and hot-melt prepreg processing routes have been explored and assessed. The hot-melt technique was successfully adopted in a pilot line production facility. Working in collaboration with the resin supply partner, a suitable Beta-staged chemistry has been developed, implemented and demonstrated. This represents a notable advance in manufacturing readiness levels of graphitic composites.
• The direct deposition technique for manufacture of filtration-free laminates has demonstrated clear feasibility to deposit and localise GNPs into composite laminate. The capability has also enabled capabilities for composite strain-sensing and localised electrical heating. These functionalities can be exploited in the context of in-situ structural health monitoring and de-icing applications in high value composite structures.
• Disbond-on-command using graphitic structural adhesive developments showed feasibility of localised heating using microwave energy. Although bonded joint detachments were attained, further development is needed to optimise for more localised effects.
• Techniques for scalable and industrially applicable delivery of the adhesive formulations using vacuum mixing and dispensing using twin cartridges have been developed.
• Graphene/graphite augmented coating developments highlighted a number of exploitable functional properties. These include, protection against electromagnetic hazards (e.g. EMI or ESD); wide area strain sensing which could be used to promote structural health monitoring and condition based maintenance of high value structures; moisture barrier effects which may be deployed to reduce environmental degradation of composite structures; fire retardancy especially through development of synergistic effects; and utilisation of the electrical heating for de-icing of aerofoil structures. Importantly, a number of the functionalities can be integrated into a single coating solution.
Work package 6
On the basis of the achieved outcomes, several industrial applications may be developed, both in aerospace and in automotive sectors, such as:
• Lightweight structures, allowing lower fuel consumptions, emissions and operating costs
• New electrically conductive coatings, with de-icing and lightning strike protection functionalities and improved fire resistance
Moreover, the project activities and experience have contributed to the development of a specific and strategic knowledge, combined with the strong position Europe already enjoys in the composites, adhesives and coatings markets. This way the project has fostered the competitiveness of the European graphene production industry and also strengthened Europe’s position in the fields of advanced composites, specialty coatings and high-performance adhesives.
Possible industrialization of PolyGraph technologies will take advantage of the work carried out for production and testing of demonstrator parts, representative of high quality products, which can be translated into higher production volumes.
Work package 7
In order for any new technology to be successfully developed, adopted and sustained in a commercial sense, it must not only achieve the aspirational performance (and cost) targets but must also demonstrate that there are no underlying causes for concern with regards to potential health risks associated with either its manufacture or use. This is particularly relevant in the development of these novel advanced materials where regulation and specific knowledge on potential health concerns can significantly lag behind their fast-paced development.
This can be seen in the development of nanomaterials in general where, in the absence of meaningful toxicity assessment and more defined regulation, some organisations are seen to adopt a zero-use policy for these advanced materials. It is therefore clear that knowledge-based understanding of potential risks is integral in ensuring not only long-term sustainability but early adoption of these technologies.
From a health and safety perspective it is clear that the development in the understanding and knowledge of the potential impact of the aerodynamic properties of graphene (and nano-platelet materials in general) has identified a potentially significant risk which may negatively impact the development of graphene and graphene-containing materials. The work carried out in PolyGraph has significantly advanced our understanding in the potential risks associated with nano-platelets. This is particularly seen to be the case in the development of novel characterisation techniques that allow us to map aerodynamic and physical size of platelets whilst isolating the respirable fraction for more scientifically robust and meaningful in vitro toxicity assessments.
This understanding of aerodynamic properties transgresses potential toxicological behaviour into the workplace environment, where detailed exposure monitoring studies have highlighted the issue of particle persistence as a risk to organisations involved in either the manufacture or use of graphene in bulk powder form. Information and knowledge gained throughout the project has served to highlight these risks in order that appropriate steps can be undertaken to mitigate potential exposure to workers involved in these activities.
In contrast to the use of graphene in bulk powder form, detailed analysis has shown that risk of exposure is significantly reduced once the graphene is either in the dispersed phase (e.g. aqueous, solvent or resin systems) or in fully cured polymer matrices. Machining of graphene-containing composites has readily shown that the graphene remains embedded within the matrix and is not liberated as a free entity. Whilst there remains a lack of information on the toxicity of graphene-containing polymers (with regards to inhalation of respirable fragments generated through machining), it is considered to be the case that the toxicity should be consistent with that of the virgin polymer (based on analogous studies conducted with other nanomaterials, including carbon nanotubes). A caveat to this is that the graphene (nanomaterial) is adequately dispersed within the matrix i.e. there are no pockets of under-dispersed powder within the cured composite.
Whilst the health and safety work-package has significantly extended the knowledge on the potential risks associated with the manufacture and use of graphene and graphene-containing composites, it is clear that much work is still required in this relatively nascent area. This is particularly the case for the toxicology community where further, more in-depth, research is required to investigate further the potential toxicity of graphene (and 2D materials in general) with a specific focus in developing a correlation between toxicological response, mechanism of toxicity and physicochemical properties.
Work package 8
Dissemination
In September 2017, PolyGraph exhibited at Graphene Week. The 5-day event was attended by approximately 800 industry professionals. Several project partners provided talks at Graphene Week, along with a “Graphene Enhanced Composites” workshop held as a parallel session. On display on the exhibition stand was two demonstration parts and several samples made within the project.
The talks given at Graphene Week were:
• Preparation and processing of large lateral size graphene material in epoxy matrix composites - Julio Gomez Cordon, Avanzare, Spain
• Estimating the life cycle costs and environmental impacts of production of GRM and GRM filled polymer formulations - Francine Amon, RISE, Sweden
• Self-sensing using graphene in thermoset composites - Han Zhang, Queen Mary University of London, UK
In October 2017, PolyGraph will exhibit at the Industrial Nanocomposites Conference, where demonstration parts and samples will be on display. A talk will be given by one of the project partners.
A training video has been produced by IOM on health and safety aspects of working with graphene enhanced nanocomposites.
PolyGraph joined the Graphene Flagship as a partnering project, enabling cross-project dissemination of results with the aim of bringing together scientists, engineers and commercial companies looking to turn graphene and related materials from academic research into real-world products.
An initial press release, detailing the launch and objectives of the project was published within the first month of the project. The press release outlined the aims of the project and the project consortium members.
Further press releases were issued throughout the project to give updates on project progress and to notify people of the project’s attendance at various events.
Throughout the project various posters, flyers and postcards were produced which detailed the aims, objectives, development and outcomes of the project. The poster, flyer and postcard allowed partners to effectively dissemination the project’s broad goals.
During the later stages of the project some flyers and a booklet were produced giving details of the automotive and aerospace case studies.
PolyGraph project partners have attended many conferences, exhibitions and workshops throughout the duration of the project where its aims, objectives and outcomes have been disseminated.
Life Cycle Costing
The initially higher cost of GRM filled polymers may be a deterrent to their acceptance for use in commercial products (from a formulation manufacturing perspective); however, when the improvements in product performance and efficiency are considered (from a consumer perspective) it is possible to show that the GRM filled products are less expensive over the lifetime of the product. This is particularly true in the transport industry, where reduced weight is a very important factor in product design.
A challenge to the acceptance of composite replacements for steel parts, whether the composite is GRM filled or not, is the recyclability of the material at the end of life. Steel, although much heavier than composite, has recycling value. Future improvements in recycling technology might shift the balance more in favour of composite replacement parts.
Dr Gary Foster
Project Manager
NetComposites
4A Broom Business Park
Bridge Way
Chesterfield
S41 9QG
United Kingdom
Tel: +44(0)1246 266 244
Email: gary.foster@netcomposites.com