Robert Chapple

This work investigates the aerosols emitted from carbon fibre-reinforced epoxy composites (CFC) incorporating nanomaterials (nanoclays and nanotubes), subjected to simultaneous fire and impact, representing an aeroplane or automotive crash. Simultaneous fire and impact tests were performed using a previously described bespoke testing methodology with the capability to collect particles released from the front/back faces of the impacted composites plus the effluents. In this work the methodology has been further developed by connecting the Dekati Low Pressure Impactor (DLPI) and Mini Particle Sampler (MPS) sampling system in the extraction chimney. The aerosols emitted have been characterized using various devices devoted to the analysis of aerosols. The influence of the nanoadditives in the matrix on the number concentration and the size distribution of airborne particles produced, was studied with a cascade impactor in the 5 nm–10 µm range. The morphology of the separated soot fractions was examined by SEM. The measurement of aerodynamic size of particles that can deposit in human respiratory tract indicate that 75% of the soot and particles released from CFC could deposit in the lungs reaching the bronchi region at a minimum. There was however, a minimal difference between the number particle concentrations or particle-size mass distribution of particles from CFC and CFC containing nanoadditives. Moreover, no fibres were found in the effluents.

Nanomaterials are usually incorporated in the polymeric resin matrix of the carbon fibre-reinforced composites (CFC) to enhance their mechanical and thermal performances. CFCs when exposed to heat/fire and impact such as in an aeroplane/transport vehicle crash, are known to release small carbon fibres, some of which could be of nanosized diameters and hence airborne. While this is still an under researched area, there is no information available on the fate of CFCs containing nanomaterials in such scenarios. To address this, we have recently developed a methodology to subject CFCs to simultaneous heat/fire and impact and collect all of the released debris from the front/back faces plus the effluents of the heated/burning composite. CFCs containing nanomaterials, namely layered double hydroxides (LDH), nanotubes (NT) and graphene oxide (GO) were subjected to varying radiant heat fluxes and 19J low velocity impact. Particle size distribution of released particles was conducted by image analysis of SEM micrographs and their agglomeration behaviour by zeta potential measurement. The presence of nanomaterials did not significantly affect the particle size distribution of the released particles; however, the heat duration and the fire had a noticeable effect, the particle size decreased with increasing heat flux and duration. From the particle size distribution and agglomeration behaviours their potential health hazards could be contemplated.

The toxicological profile of particulates released from carbon fibre-reinforced composites (CFC) incorporating nanoadditives, under impact and fire conditions (e.g. aircraft crash), is unknown to date. Our aim was to investigate the effects of simultaneous impact and fire on the physicochemical features of the particles released from CFCs produced from a graphene oxide (GO)-reinforced epoxy resin and the consequences on its toxicological profile. CFC samples with (CFC+GO) or without GO (CFC) were subjected to simultaneous impact and fire through a specific setup. Soot and residues were characterised and their toxicity was compared to that of virgin GO. Virgin GO was not cytotoxic but induced pro-inflammatory and oxidative stress responses. The toxicity profile of CFC was similar for soot and residue: globally not cytotoxic, inducing a pro-inflammatory response and no oxidative stress. However, an increased cytotoxicity at the highest concentration was potentially caused by fibres of reduced diameters or fibril bundles, which were observed only in this condition. While the presence of GO in CFC did not alter the cytotoxicity profile, it seemed to drive the pro-inflammatory and oxidative stress response in soot. On the contrary, in CFC+GO residue the biological activity was decreased due to the physicochemical alterations of the materials.

A novel laboratory scale testing equipment has been designed and developed, which combines impact and heat/fire conditions to enable the testing of composite laminates, including the ability to capture debris/particles released during the test. This incorporates a pendulum impactor to create impact whilst the sample is exposed to a cone heater at a particular heat flux for a specified period of time.
A protocol for testing samples under different conditions and capturing particles released, both from the front and back faces, along with effluents has been provided. A carbon fibre-reinforced epoxy composite was impacted whilst being exposed to different heat fluxes for a range of time periods. A loss of stiffness related to the heating exposure time was found to affect the damage type. At lower heat fluxes, the captured particles included broken carbon fibres, decomposed resinous particles and resin coated fibres. Quantitative and morphological analyses of captured particles demonstrated that the sizes of decomposed resin particles and fibres reduced with longer exposure time or increased heat flux. This information could be useful to provide insight into potential health hazards of components of the composites.