Effect of Fibrous Nucleating Agent on Shear-induced Crystallization for Polypropylene

We investigated the effect of shear history on the crystallization behavior of isotactic polypropylene (PP) containing a fibrous nucleating agent, i.e., 1, 3 : 2, 4-bis-o-(4-methylbenzylidene)-Dsorbitol (MDBS), using a polarized optical microscope attached with a parallel-plate shear device. The addition of MDBS greatly enhanced the crystallization temperature of PP with an accelerated crystallization rate. Although shear history applied during cooling barely affected the crystallization temperature for the sample containing MDBS, it greatly enhanced the PP orientation, even with a low shear rate. This was attributed to the formation of a pseudo shish-kebab structure, in which MDBS acted as the shish. It was also found that the addition of MDBS reduced the amount of β -form crystals, while PP without MDBS exhibited β -form crystals after applying an appropriate shear history.