Preparation, Structure, and Properties of an Isotactic Polypropylene Film with Ultrahigh Content, Ordered, and Continuous β-Transcrystallinity

beta-Transcrystallinity (beta-TC) of polypropylene (PP) is a novel kind of crystal that is of significant importance. Owing to the low content, discontinuity, and random distribution of beta-TC obtained by traditional methods, there has not been significant research on this particular crystal. Thus, its formation mechanism and growth law remain unclear and their impact on performance is still inclusive. In this study, continuous and ordered beta-TC was induced via the two-dimensional interface of an epoxy resin plate that contained the beta-nucleating agent. Therefore, we achieved a PP film composed of pure beta-TC without any agents in the bulk and a beta-crystal content of up to 92%. According to the two-dimensional wide-angle X-ray diffraction measurements, the crystallography orientation of the film greatly differed as the direction of observation changed, depending on which the growth model of beta-TC within the film was proposed. Furthermore, it was proved by the in situ two-dimensional small-angle X-ray scattering measurement and biaxial stretching test that the mechanical properties and pore-forming properties of the beta-TC film were significantly improved because of its peculiar crystalline structure.