Heterogeneous nucleation of short glass fibre-polypropylene composites

Abstract

The heterogeneous nucleation of polypropylene homopolymer and discontinuous glass fibre (critical fibre length, L c ⩾ 3 mm) reinforced polypropylene was performed by using sodium benzoate as the nucleating agent. Isothermal crystallization of the compression-moulded nucleated polypropylene, non-nucleated polypropylene, nucleated composite and non-nucleated composite was carried out over a temperature range of 370–398 K. Comparison of the shift in the bulk crystallization peak temperatures, as well as the rate of isothermal crystallization of the samples, showed that the incorporation of the nucleating agent resulted in a significant improvement in the crystallization of the polypropylene homopolymer. The short glass fibres nucleated the polypropylene matrix to the extent that the crystallization and morphology of the matrix differ appreciably from those of the homopolymer. Detailed Avrami kinetic analysis was carried out at 390 K for the samples and values of the Avrami constants K and n, ranging from 2.3 × 10 −5 to 2.4 × 10 −3 and 2.01 to 1.66 for the polypropylene homopolymer to the nucleated composite, respectively, were obtained. Optical microscopic analysis showed spherulitic crystallization for the homopolymer, crystallitic crystallization for the nucleated polypropylene, and mixed crystallitic and axialitic crystallization for the discontinuous composite.