Investigation of the Transcrystallised Interphase in Fibre-Reinforced Thermoplastic Composites

Abstract

The occurrence of transcrystallisation in fibre-reinforced polypropylene is shown to depend on the type of fibre used. The list of fibres which transcrystallise polypropylene is not identical to that for other semicrystalline thermoplastics. Furthermore, the ability of aramid fibres and high-modulus carbon fibres to induce transcrystallisation in polypropylene depends on the crystallisation temperature and the polymer molecular weight. With one particular polypropylene, at crystallisation temperatures below 138 °C, the growth rate of the transcrystallised region around three different types of fibre in polypropylene was found to be the same as the growth rate for the bulk spherulites. Above 138 °C these fibres did not nucleate transcrystallinity, although spherulites were still nucleated in the bulk. Further more it was possible, through the application of shear, to induce a crystalline region around fibres embedded in polypropylene at temperatures where transcrystallisation was not obtained in quiescent crystallisation. When studied using polarised light microscopy this region could not be distinguished from a transcrystallised region. We therefore propose that transcrystallisation and stress-induced crystallisation may be related.