The effect of thermally desized carbon fibre reinforcement on the flexural and impact properties of PA6, PPS and PEEK composite laminates: A comparative study

Commercial carbon fibre (CF) fabrics are frequently equipped with an epoxy-based (EP) sizing, which is required for fibre protection during weaving but unsuitable for subsequent thermoplastic processing due to incompatibility. The present study investigates a heat treatment method of CF fabrics in order to remove the incompatible sizing and promote interfacial adhesion with thermoplastic matrices through the oxidised carbon surface. The removal of the EP-sizing from CF fabrics (desizing) was conducted by infrared-irradiation (IR) in air atmosphere at 400 °C. IR-desized CF fabrics were confirmed to be free from sizing residues by SEM imaging and thermogravimetric analysis. Subsequently, CF-PA6, CF-PPS and CF-PEEK thermoplastic composite laminates (TPCL) were manufactured by means of film stacking and hot compression moulding with fibre volume fractions ranging from 45-47%. For comparative purposes, the in-house moulded TPCL were benchmarked against state-of-the-art industrial TPCL in 3-point flexural, short-beam flexural and Charpy impact tests. Overall, very similar performance was attained between IR-desized TPCL and their industrial counterparts. Excellent wet-out and interfacial adhesion of IR-desized CF was observed from SEM imaging of fractured laminates. Conversely, TPCL prepared from EP-sized CF fabrics were found to be neither sufficiently consolidated nor thoroughly wetted out by the thermoplastic matrix, confirming poor interfacial compatibility. The correspondingly poor mechanical performance of EP-sized TPCL emphasised the importance of EP-sizing removal.