Study on the fracture behavior of annealed immiscible polypropylene/poly(ethylene oxide) blend

Immiscible polypropylene/poly(ethylene oxide) (PP/PEO) blend was injection molded and the specimens were annealed at different temperatures (90-150 °C). Dynamic mechanical analysis (DMA) was used to investigate the relaxation behavior of the PP matrix before and after being annealed. The fracture behavior of the annealed specimens was comparatively investigated by notched Izod impact and single-edge single-notched three-point bending measurements. The fractured surface morphologies obtained from different measurements were characterized by using scanning electron microscopy (SEM). The results showed that annealing not only improved the mobility of chain segments but also improved the damping behavior of PP matrix. Greatly increased impact strength was observed for the annealed PP/PEO specimens. The formation of a saw-shaped plastic deformation zone at the edge of the annealed specimen was suggested to be the main reason for the increased impact strength. The results also showed that annealing caused a change from plain strain induced fracture to plain stress induced fracture. Further results obtained from three-point bending measurements showed that annealing was favorable for the enhancement of the maximum load (Fmax), the critical stress intensity factor (Kc) and the critical strain energy release rate (Gc) of the immiscible PP/PEO blend.