The Fracture Behavior Evaluation And Investigation Of Polypropylene/elastomer Blends

This work is an attempt to study the effect of elastomer content on the plane-stress fracture performance of polypropylene (PP)/elastomer blends, using the essential work of fracture (EWF) method.For PP/polyolefin elastomer (POE) blends, the influence of POE content on the fracture behavior and fracture surface of PP/POE blends was evaluated. With increasing POE content, specific total work (w_f) and specific work for necking and subsequent fracture (w_n) was increased. The yield stress (σ_n) of the blends was decreased and the extension at failture (e_b) Was increased. The height of DOPZ and that of IOPZ were both increased. For the fracture surface, the length of the crack stable growth region was increased and the length of the brittle fracture region was decreased.For injection molded samples and compression molded samples of PP/POE blends, the validity of EWF evaluation was verified at first. The crack propagation and the character, size and development of the plastic deformation zone ahead of the crack tip were observed and illustrated on line. The influence of POE content on the essential work of fracture, plastic deformation work, crack opening displacement, etc., was analyzed. The distribution of fracture energy in different stages was discussed through a rational method for energy partition. The critical crack opening displacement (COD)_C method was employed to predict the specific essential work of fracture. It was found that the plane-stress EWF approach worked well for the PP/POE blends, which all behaved in a typical ductile tearing manner as full yielding of ligament and stable propagation of crack. The specific essential work of fracture (w_e) was increased with increasing POE content. The dominant factor which affected w_e was the necking and subsequent fracture term (w_e,n). The specific non-essential work of fracture (βw_p) was increased slightly with increasing POE content. Finally, it was shown that w_e could be predicted reasonably well via crack opening displacement (COD) values. For the different of orientation and melt pressure of injection molded and compression molded, w_e andβw_p of injection molded were both larger than that of compression molded.For dynamically vulcanzized PP/Ethylene-propylene-diene terpolymer (EPDM) blends, PP and EPDM were dynamically vulcanized with dicumyl peroxide (DCP) added, using a two-step method of even dispersion for DCP in EPDM at first and then crosslinking at elevated temperature. The results showed that though both chain scission and crosslinking occurred, the crosslinking reaction predominated in this process and the number of EPDM particles was increased, accompanying with the reduction in particle size and uniform dispersion. Differential scanning calorimetry (DSC) results indicated the existence of PP/EPDM graft copolymer. The EWF results showed that both w_e and w_p increased with increasing EPDM content, the fracture toughness and plastic energy consumption could be improved simultaneously and the ratio of them could be controlled by adjusting EPDM and DCP content.