Experimental detection of a transcrystalline interphase in glass-fibre/polypropylene composites

Crystallization and melting behaviour of polypropylene in glass-fibre-reinforced composites have been investigated by means of differential scanning calorimetry. Composites with differently size-coated glass fibres show different behaviour both in dynamic and isothermal crystallization. A high crystallization rate and a short induction time were observed for composites with unsized fibres at isothermal crystallization. Glass fibres sized with aminosilane and polypropylene film-former revealed a quantitatively separable two-step crystallization process. With the assignment to the transcrystallization and spherulitic crystallization the thickness of the transcrystalline PP interphase in this composite could be estimated to about 1 μm. The influence of transcrystallinity on the mechanical properties was discussed.