CRYSTALLIZATION BEHAVIOR AND EFFECT OF THERMAL-TREATMENT ON FRACTURE PERFORMANCE OF GLASS FLAKE REINFORCED POLYPROPYLENE

In this work, the role of the interface and matrix morphology in determining the fracture behavior of glass flake reinforced polypropylene is investigated. Differential scanning calorimetric analysis shows that silane coupling agent modifies the crystallization behavior of the polypropylene matrix. Silane treated glass flakes prepared by dry blending are found to induce nucleation and decrease the rate of development of the crystalline entities during the crystallization process. This effect is attributed to the physisorbed layer of silane on the glass flakes. The effect of matrix morphology on the fracture performance is analyzed by fracture mechanics. An increase in matrix crystallinity in pure polypropylene and in glass flake/polypropylene composites leads to a reduction in the maximum crack growth resistance. The lower ductility of a more crystalline matrix results 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 important in the case of pure polypropylene and untreated glass flake polypropylene composites, this effect is 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 seems to inhibit the effect of matrix morphology on the fracture behavior of glass flake/polypropylene composites.