Thermo-oxidative ageing effect on mechanical properties and morphology of short fibre reinforced polyamide composites – comparison of carbon and glass fibres

Abstract

The present paper examined the thermo-oxidative ageing behavior of short carbon fibre reinforced polyamide 6 composites (CF/PA6), in comparison with commercial glass reinforced composites (Ultramid® B3WG7). The mechanical results revealed that the tensile strength of CF/PA6 composites (retention above 90%) was well maintained, while the notched Izod impact strength of both CF/PA6 and Ultramid® B3WG7 were continuously decreased during the ageing process. Annealing effects on PA6 and chain arrangement were found in the initial ageing stage, and a better thermal stability of CF/PA6 compared with the Ultramid® B3WG7 sample was observed from the TGA curves as the ageing time was prolonged. A noticeable color transition from white to black was observed in Ultramid® B3WG7 samples when the increasing ageing temperature. The ageing process also resulted in topography damage with matrix cracks and fibre/matrix interfacial debonding due to chain scission, oxidization and formation of chromophoric groups of polyamide molecules, which was illustrated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Furthermore, metallographs of polished cross-sections of Ultramid® B3WG7 demonstrated the evolution of an oxidized layer of the composites at increased ageing temperatures for prolonged ageing time, which was ascribed to the contribution of mechanical changes that play an important role at high ageing temperatures.