Evaluation of Recycled Carbon Fibre/Epoxy Composites: Thermal Degradation Behaviour of Pyrolysed and Virgin Carbon Fibres Using Thermogravimetric Analysis

Abstract The recycling of carbon fibres is a critical step in the reutilization of carbon fibres in a closed-loop economy. Evaluation of the recovered fibres regarding their mechanical properties, purity of the fibre surfaces and thermal stability are key points when exploring new high performance applications. This publication reports about the investigation of the thermal stability of pyrolysed carbon fibres and virgin fibres alone and in composite materials using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). A commercial pyrolysed woven fabric (unaltered in length) was processed like virgin high tenacity carbon fibre to investigate the recycling potential of unchopped fibres and demonstrate their recycling without further down-cycling. Identical components of virgin and pyrolysed fibres were manufactured. These composite materials as well as the fibres solely were compared regarding their thermal degradation behaviours as a function of heating rates as well as temperature ranges in different gas environments. For further analysis of the data a kinetic study was performed. In addition, light microscopy and SEM imaging was used to visualize and investigate the samples. A slight shift to lower temperatures in thermal decomposition behaviour of the pyrolysed carbon fibres was observed. The decomposition of the matrix was similar in the TGA measurements but possibly, due to the missing sizing and lower fibre orientation a higher mass fraction of resin as well as higher activation energy values were calculated. The degradation of the carbon fibre fraction showed the largest variation. This is assumed to be due to the carbon fibre crystal structure but for verification, additional work needs to be performed.