Summaries published as Polygraph draws to a close
In November 2017 the FP7 PolyGraph project came to a close after four years of work into the up-scaled production of graphene.
The project aimed to develop a process in which graphene could be produced and dispersed "in-situ" within thermosetting polymer resins, using relatively inexpensive expanded graphite as a starting material. These materials are suitable for use in a number of key applications where improvements are required in the strength, stiffness, toughness, electrical conductivity and thermal and barrier properties of polymers, such as fibre-reinforced composite resins, coatings and adhesives.
SAFENANO led the health and environmental impact assessment work package, involving detailed characterisation and assessment of the potential risks presented by materials and processes developed throughout the duration of the project.
The main objectives of work package 7 were focused on identifying the potential hazards associated with graphene-family nanomaterials (GFN) and the potential for these materials to be released into the workplace air during the handling and processing activities undertaken throughout the project. Hazard assessment was conducted by means of a detailed review of peer-reviewed published literature combined with in vitro studies of materials generated within the scope of the project. Potential exposure to GFN materials was undertaken through detailed measurements undertaken at seven partner sites. Aspects from the Hazard and Exposure assessments were then consolidated to provide pragmatic Risk Management Guidance document for understanding and addressing the potential risks associated with the manufacture and use of graphene and graphene-containing composites.
The objective of the life-cycle assessment (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.
Of the various physico-chemical properties of GFN, it is their peculiar plate-like structure that has most caught the interest of toxicologists. There is evidence to show that very thin platelets of large (> 10 µm) lateral diameter can possess a sufficiently small aerodynamic equivalent diameter (Dae) to allow alveolar deposition. This has a direct consequence for the clearance mechanisms which should not normally have to deal with such large particles, where difficulty will arise in clearing these particles from the lung. The deposition of large particles in the lung has been shown to result in the generation of localised inflammation, granuloma formation and scarring (fibrosis). The mechanism of toxicity presented by such particles is the cornerstone of what is known as the Fibre Pathogenicity Paradigm. As evidence continues to emerge with regards to the aerodynamic properties of GFN, it can be argued that that Fibre Paradigm should be extended to include nano-platelets.
The toxicity of PolyGraph materials was studied using in vitro testing with alveolar macrophages. As the lung is the main target of concern in relation aerosol exposure, a respirable fraction of the test particles was generated using methodology developed within the project. Bulk and respirable powders were assessed for cytotoxicity, oxidative stress, pro-inflammatory effects and 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.
Whilst a significant amount of exposure and contextual data was gathered across seven partner site visits, common themes across the sites were identified and used to consolidate key findings. These contained information on control measures, cleaning and waste disposal, elemental carbon analysis, aerodynamic sizing, persistence potential of platelets and issues surrounding material feed. Whilst results were 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. For activities conducted in the open workplace, existing LEV systems (e.g. flexible trunking or other extraction systems) were not seen to be capable in containing release and preventing migration into the surrounding work areas. Where GFN had been released their low aerodynamic properties may present an issue of persistence where theory suggests that these platelets could remain in the surrounding air for days and weeks after completion of activities, presenting a potential longer-term exposure risk. 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.
The LCA results show that the service life of the demonstrator parts (the use phase of the life cycle) has the highest environmental impact by far. The coating and adhesive parts had lower overall impacts than their references, 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.
More information about the outcomes of PolyGraph, including contributions from other project partners, can be found on the project website.Back to news listing