Transfer of load from matrix to fiber in self-reinforced polymer composites

The tensile properties of self-reinforced polypropylene composites, obtained by rapid extension of an isotactic polypropylene/atactic polypropylene melt, have been measured and correlated to morphological parameters derived from x-ray experiments. The longitudinal morphology of the core-fibrils is found to be independent of sample composition, while the lateral thickness of the fibers varies between 220 Å for iPP and 110 Å for the blend containing 50 wt.% aPP. Critical fiber lengths, as a function of sample composition and the elastic modulus and the yield stress of the fibers, could be determined. While the number of corefibrils increases with mass fraction of atactic polypropylene, the length of the lateral interface between fiber and matrix and the interface volume decreases with increasing aPP mass fraction. It is shown that this interface is responsible for the mechanical behavior of the composite by effecting the transfer of load from matrix to fiber.