Anisotropic microstructure-impact fracture behavior relationship of polycarbonate/polyethylene blends injection-molded at different temperatures

Abstract

Polycarbonate (PC)/polyethylene (PE) blend was injection molded at three temperatures: 190, 230 and 275 °C. Due to different deformability of PC phase at the different molding temperatures, the blends exhibit different morphologies. The sample molded at 190 °C only contained many uniformly dispersed spherical PC particles due to the incapability of flow and deformation of PC phase at this temperature. The samples molded at both 230 and 275 °C showed typical anisotropic (skin–core) structures, and there were many injection-induced PC fibers in the sub-skin layer. The DSC measurement showed that higher molding temperature leads to higher crystallinity and more perfect crystals of PE phase. The impact fracture of three bars behaves differently in the following aspects: (1) overall fracture surface, (2) craze and micro-void formation (stress whitening), (3) fibrillation of PE, and (4) plastic deformation of PC dispersed phase. As the molding temperature increases, the stress whitening becomes stronger, the shear lips become thicker, the amount of the stick–slip lines and the micro-voids increases, and the voids become smaller. Moreover, upon impact fracturing, numerous fibrils of PE were formed in 230- and 275-bars, at the same time, obvious plastic deformation of PC fibers occurred in the 275-bar. All these microscopic features demonstrate the impact toughness increases with molding temperature. Lamellae texture evolution and high interfacial contact were employed to partially interpret the impact fracture behavior. Numerous filaments generated around PC particles on the fracture surfaces, which bridged the PC particles and PE matrix, indicated a high interfacial adhesion between PC particles and PE matrix.