Life Cycle Strategies for Improving Mechanical and Environmental Performance of Recycled Carbon Fibre Composite in the Automotive Industry

Abstract

Carbon fibre reinforced polymer (CFRP) is increasingly used in the wind, aerospace and sporting industries due to its properties such as a high strength-to-weight ratio, good corrosion resistance and low thermal expansion. The increasing use of CFRP is generating increasing carbon fibre wastes. These wastes are potentially sustainable, low-cost yet high-quality sources of carbon fibre for vehicle lightweighting in the automotive industry. However, the current recycling process for carbon fibre leads to a significant reduction in the mechanical performance of CFRP. CFRP is currently down-cycled from structurally critical applications to those with low structural significance. Improving the mechanical performance of recycled CFRP (rCFRP) is beneficial for widening its application in the automotive industry and moving carbon fibre towards material circularity.

This work investigates the potential strategies for improving the mechanical performance of rCFRP for automotive applications. A research method integrating Life Cycle Assessment (LCA) and experimental investigation was adopted to answer the research question. First, primary data regarding the life cycle of a state-of-the-art rCFRP vehicle part was collected through a collaboration with an automotive manufacturer in the USA. The part was analysed to investigate the most impactful areas in carbon fibre recycling on the mechanical performance of the rCFRP parts. Scenario analysis was also conducted to compare the impact of different recycling stages. An experimental investigation was conducted to evaluate the need for pre-recycling sorting of CFRP wastes to address the varying tensile property reductions of carbon fibre during recycling. The potential of fibre architecture preservation as a recycling strategy for improving the physical and mechanical properties of rCFRP was also experimentally investigated in a lab-scale recycling facility. Finally, based on primary data from the experimental investigations, the implications of the two carbon fibre recycling strategies, waste sorting for reducing variations in fibre tensile properties and fibre architecture preservation, on the mechanical and environmental performance of rCFRP in the automotive industry were evaluated.

Undertaking a Life Cycle Assessment of the current practices of using rCFRP in automotive production identifies significant reductions in the mechanical performance of rCFRP as a result of the pre- and post-recycling stages. Improvements in the architecture of recycled carbon fibre (rCF) and the fibre volume fraction of rCFRP would lead to the most significant reduction in the life cycle environmental impacts of rCFRP vehicle parts. Through experimental investigation, it was found that carbon fibres with surface treatments are subjected to increased reductions in tensile strength during recycling. This is due to the interactions between fibre, sizing layer and fibre surface functional groups. Sorting carbon fibre wastes based on fibre surface treatments is important to improve the consistency in the applicability of rCF in structural applications. Moreover, preserving carbon fibre architecture during recycling reduces the flexural modulus reduction of CFRP after recycling by at least 51%, as compared with the current recycling practice. The use of architecture-preserved rCF in producing a vehicle roof panel exhibits an overall reduction in the life cycle environmental impacts compared with the steel baseline and the current rCFRP.

Pre-recycling sorting of carbon fibre wastes based on fibre surface treatments and fibre architecture preservation are effective recycling strategies for improving the mechanical and environmental performance of rCFRP in the automotive industry.