Flowing Performance, Microstructures, and Fracture Toughness of Dynamically Vulcanized PP/EPDM Blends

The fracture behavior of polypropylene/ethylene-propylene-diene terpolymer (100/8) blends with different microstructure was investigated using the essential work of fracture approach. Ethylene-propylene-diene terpolymer and dicumyl peroxide were mixed in a single-screw extruder at 140°C, and the crosslinking reaction had hardly taken place at this temperature. Then the reactive extrusion of ethylene-propylene-diene terpolymer and polypropylene was performed on a twin-screw extruder at a temperature range of 160-210°C and ethylene-propylene-diene terpolymer was crosslinked in this process. Various crosslinking density of ethylene-propylene-diene terpolymer in polypropylene/ethylene-propylene-diene terpolymer (100/8) blends was obtained by varying the concentration of dicumyl peroxide. With increasing dicumyl peroxide concentration, melt flow rate of the blends gradually increased but the increasing trend was slowed up. The degradation reaction of polypropylene was markedly restrained by adopting such a processing method. From the result of scanning electron microscopy, the size of ethylene-propylene-diene terpolymer particles was reduced and a more uniform particle size distribution was obtained. The existence of polypropylene/ ethylene-propylene-diene terpolymer graft copolymer was demonstrated by differential scanning calorimetry and the negative effect of the graft copolymer on the crystalline rate of polypropylene macromolecules which were grafted onto ethylene-propylene-diene terpolymer chains was validated. The specific essential work of fracture (ω e ) increased markedly with increasing dicumyl peroxide concentration for the blends prepared. When the concentration of dicumyl peroxide was 0.3 wt% of ethylene-propylene-diene terpolymer content, the value of ω e of the dynamic vulcanized blends was about 165% as that of polypropylene/ethylene-propylene-diene terpolymer simple blends or polypropylene, while the specific plastic work (βω p ) was still larger than that of polypropylene.