THE EFFECT OF TRANSCRYSTALLINITY ON THE INTERFACIAL CHARACTERISTICS OF POLYPROPYLENE ALUMINA SINGLE-FIBER COMPOSITES/

The effect of processing parameters such as crystallisation temperatur e and cooling rate on the crystallisation and interfacial morphology o f isotactic polypropylene containing a single alumina fibre has been i nvestigated using a hot stage microfurnace. It was found that a transc rystalline layer (TL) could only be produced if the fibre was pulled t hrough the supercooled matrix, and that the thickness and growth rate of this TL depended upon the isothermal crystallisation temperature, b ut not on the cooling rate. The higher the crystallisation temperature , the slower the growth rate. Both alpha-monoclinic and beta-hexagonal crystal structures have been identified in the TL, with the beta crys tals only being induced in areas of existing alpha crystals. The alpha region transforms into beta crystals except for a small region at the fibre/matrix interface. These beta crystals grow at a faster rate tha n the alpha crystals and were found to melt at 157 degrees C, compared to 170 degrees C for the alpha crystals. The single fibre fragmentati on test was then used to characterise the interfacial adhesion in syst ems both with and without a TL. It was found that in systems containin g a TL, the fragment lengths at saturation were related to the thickne ss of the TL. Additionally, when the TL was not present, the cooling r ate influenced the stress transfer efficiency.