Crystallization behavior and effect of thermal history on fracture performance of glass flake reinforced polypropylene

In this work, the role of interface and matrix morphology in fracture behavior of glass flake reinforced polypropylene was investigated. Differential scanning calorimetric analysis showed that a silane coupling agent modified the crystallization behavior of the polypropylene matrix. The presence of dry blend silane treated glass flakes in polypropylene was found to induce the nucleation process and decrease the overall rate of crystallization. The effect of matrix morphology on the fracture performance was analyzed by post-yield fracture mechanics on samples of different levels of crystallinity. An increase in matrix crystallinity in pure polypropylene and glass flakes polypropylene composites led to a reduction in the maximum crack growth resistance. The lower ductility of a more cystalline matrix resulted in a reduction of the energy dissipated in the matrix stretching and therefore, a concomitant decrease in the fracture energy. Although the effect of matrix morphology seemed to be very important in the case of pure polypropylene and untreated glass flake polypropylene composites, this effect was found to be negligible for the silane treated composites. Nevertheless, microscopic observation of the fracture surfaces of silane treated composites also revealed a reduction in the ductility of the matrix in highly crystalline samples. An improvement in the matrix-filler interface seemed to inhibit the effect of matrix morphology on the fracture behavior of glass flake polypropylene composites.