Hygrothermal aging and fracture behavior of short-glass-fiber-reinforced rubber-toughened poly(butylene terephthalate) composites

The fracture behavior of injection-molded poly(butylene terephthalate) (PBT), core–shell rubber toughened PBT (PBT-CSR) and their related short-glass-fiber composites have been investigated. The investigation was focused on the effect of internal parameters, i.e. rubber and/or glass-fiber content and external parameters, i.e. testing temperature, deformation rates and hygrothermal aging on the fracture behavior of these materials. The fracture properties of the various materials were determined on static-loaded compact tension specimens. It was shown that the tensile and fracture behavior of PBT and its related composites is affected by both internal and external parameters. A significant enhancement of both fracture parameters, i.e. fracture toughness, Kc, and energy, Gc, was achieved by the combination of CSR impact modifier and glass-fiber reinforcement, although the values of both Kc and Gc were slightly lower than those of PBT glass-fiber composites. Poor retention of tensile and fracture properties on exposure to hygrothermal aging at 90°C was observed in all materials and these properties could not be restored by subsequent drying. Qualitative evidence from scanning electron microscopy (SEM) indicates that severe hydrolytic degradation of the PBT matrix has caused permanent damage to the materials. The superior retention and recovery of the fracture properties of PBT-CSR-glass fiber as compared to PBT-glass fiber is an indication that the combination of glass fiber and core–shell rubber produced a synergistic effect on the fracture behavior of PBT under such adverse conditions. The failure modes of PBT and the related composites, assessed by SEM fractographic studies are discussed.