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 stateof-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.

Automated summary

The study investigated the use of infrared irradiation for desizing CF fabrics to enhance interfacial adhesion with thermoplastic matrices, achieving similar performance to industrial counterparts. Conversely, TPCL prepared from EP-sized CF fabrics showed poor consolidation and wetting out by the thermoplastic matrix, underlining the importance of removing EP sizing.