Effects of Nucleating Agents on Microstructure and Fracture Toughness of Poly(propylene)/ethylene-propylene-diene Terpolymer Blends

The effects of nucleating agents (NAs) on fracture toughness of injection-molded isotactic poly(propylene)/ethylene-propylene-diene terpolymer (PP/EPDM) were studied in this work. Compared with PP/EPDM blends without any NA, PP/EPDM/NA blends show very small and homogeneous PP spherulites. As we expected, PP/EPDM blends nucleated with beta-phase NA aryl amides compound (TMB-5) present not only a significant enhancement in toughness but also a promotion of brittle-ductile transition. However, the addition of a-phase NA 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) has no apparent effect on the toughness of the blends. The impact-fractured surface morphologies of such samples were analyzed via scanning electronic microscope (SEM). More detail work about the toughening mechanisms of elastomer and NA based on elastomer particles size and matrix crystal structures were carried out. Our results suggest that, besides the crystal structures of matrix, the elastomer particles size and size distribution plays an important role in controlling the toughening effect of nucleated PP/elastomer blends. The smaller the elastomer particles size and lower the polydispersity, the more apparent the synergistic toughening effect of NA and elastomer is. This investigation provides a fresh insight into the understanding of toughening mechanism of elastomers in PP blends and facilitates to the design of super toughened PP materials. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 46-59, 2009