Thermal Treatment Effect on Transcrystalline Interphase and Interfacial Shear Strengths of Glass Fibre / Polypropylene Composites

To investigate the influence of thermal treatment and interfacial crystalline structure on interfacial shear strength of glass fibre reinforced polypropylene composites (GF/PP), the transcrystalline samples were prepared by isothermal crystallization at 135ºC, while the quenched samples without transcrystallization were obtained by quick cooling at the rate of 20ºC/min. In the next step, the transcrystalline and the quenched specimens were each treated at various temperatures of 70ºC, 100ºC and 130ºC, and the interfacial shear strength (IFSS) of these specimens was measured by the microbond test. The results demonstrated that, before thermal treatment, the interfacial shear strength of the transcrystalline specimen is much smaller than the quenched composite specimen. The shear debonding of the trans-crystalline specimen occurred at the rim where the transcrystalline region met the spherulites, because the shear debonding of the quenched specimen happened at the PP and glass fibres interfaces. Whereas, after thermal treatment the shear debonding of the transcrystalline specimens, as same as quenched specimens, occurred at the interfaces of PP and glass fibres. The interfacial shear strength (IFSS) of the trans-crystalline specimen also increased the same as that of the quenched cases. Therefore, we conclude that transcrystallinity alters the failure location at interfacial region and thus it affects the interfacial shear strength. Both the interfacial shear strength of the transcrystalline and that of the quenched samples can be improved by thermal treatment.