Optimisation of CFRP composite recycling process based on energy consumption, kinetic behaviour and thermal degradation mechanism of recycled carbon fibre

Abstract

Abstract Pyrolysis is a thermo-chemical method to recover clean fibres from carbon fibre reinforced polymer (CFRP) composite waste under oxygen-free conditions. To ensure the recovery quality and economic efficiency of reclaimed fibres, thermal decomposition of CFRP needs to be guided by the kinetic analysis. This paper investigates the kinetic behaviour of CFRP thermal decomposition at temperatures of up to 800 °C. A thermo-gravimetric method is used to monitor the thermal decomposition of CFRP samples during the pyrolysis process. The activation energies (E) required for different conversion fractions (α) are evaluated based on five different kinetic models: four Arrhenius-type model-free methods (Friedman, OFW, KAS and Starink) and one curve fitting method (Coats-Redfern). Pyrolysis of CFRP composite wastes show that the process consists of two stages, where majority of the polymer matrix (55%) is removed in the first stage of reaction. During stage one and up to 425 °C, lower heating rates successfully lead to higher conversion fractions with lower activation energies. Moreover, by investigating physical characteristics of the recycled fibres using scanning electron microscopy (SEM) and conversion kinetics of the recycling process, it is shown that pyrolysis of the composite remains efficient until 425 °C and an oxidation process up to 550 °C is required to achieve high quality recycled carbon fibre (rCF) products. The outcomes of this research contribute to optimisation of process variables and development of highly efficient and cost effective CFRP recycling method using pyrolysis technique.