The Research Progress of Tailoring High-performance Crystalline Structures in Isotactic Polypropylene

Isotactic polypropylene (iPP) is one of the general plastics in the world. Improving the comprehensive mechanical properties of iPP is of great importance. On the basis of understanding the polymorph phenomenon and the structural sensitivity to processing conditions of iPP, it is a key way to realize the self-toughening and self-enhancing of iPP via controlling the condensed structure to appear as β-modified crystals and anisotropic crystals like shish kebab. In recent years, lots of research related to the cultivating methods of β-form iPP and the design of iPP crystalline morphology have been carried out, and the approaches applied in this area are mainly about the adjusting of processing stress field, processing temperature field and heterogeneous nucleators. Under the conditions of increasingly strengthened stress and temperature fields, the crystalline structures of iPP incline to transforming from rich α-modified spherulites to rich β-form crystals and to rich α-form shish kebab. Moreover, recent research has verified that the addition of fibrous β nucleating agents, can promote the drastic increment of orderly-stacked β lamellas during flow forming process. Thus, this paper aims to introduce and summarize the recent progress and theories corresponding to the tailoring of β-form crystals and crystalline morphologies of iPP.