Assessment of carbon fiber composite recycling

Carbon fiber reinforced plastics (CFRP) usually consist of carbon fibers arranged in an engineered pattern and a thermoset resin such as epoxy serving as the matrix. The carbon fiber (CF) provides extremely high modulus of... [ view full abstract ]

Carbon fiber reinforced plastics (CFRP) usually consist of carbon fibers arranged in an engineered pattern and a thermoset resin such as epoxy serving as the matrix. The carbon fiber (CF) provides extremely high modulus of elasticity or strength compared to traditional metallic alloys while the resin matrix provides damping capability or shock absorbance. The unique properties of such composite material systems attract great attention from wind-turbine, aeronautical, automotive and high-end sports equipment industries that seek materials with high performance-to-weight ratio. Despite the high annual growth of carbon fiber production that reached 28,000 tons in 2006 with a price of 50-200 USD/kg of CF, the recycling technology of CFRP remains far behind the manufacturing advances most likely due to the very nature of composites – two dissimilar materials (i.e. fiber and resin matrix) highly mixed together that gives rise to the desired properties yet presents challenges for separation during recycling. Given the high price of virgin CFRP, the current end-of-life disposal options such as landfilling and mechanical crushing don’t allow much recovery of the economic value and presents substantial disposal cost which suggest an economic incentive to recycle CFRP.

Other than the economy of recycling, this study quantifies the environmental impact of recycled carbon fiber (rCF) via pyrolysis at 500°C. Since rCF has been shown to retain up to 90% of the properties of vCF, we compare carbon fiber recycling to virgin polyacrylonitrile (PAN)-based carbon fiber production. We find that the pyrolysis process under laboratory-scale conditions produces global warming potential (GWP) of around 7 kg CO₂ eq/kg of rCF and requires cumulative energy demand (CED) of around 110 MJ/kg of rCF. The results are compared to vCF production under both laboratory scale and industrial scale. In both cases, the environmental impact of rCF via pyrolysis is significantly lower due to lower energy consumption from the relatively low process temperature of 500°C. This presentation will also comment on the continued challenges with carbon fiber recycling despite these potential environmental benefits.