Fabrication of Multilayered β‑Form Transcrystallinity in Isotactic Polypropylene for Achieving Optimized Mechanical Performances
journal contributionposted on 07.12.2020, 19:46 by Lu He, Shanshan Luo, Jiabin Shen, Shaoyun Guo
Herein, a series of multilayered materials consisting of alternating isotactic polypropylene (iPP) layers and cross-linked iPP (cPP) layers were fabricated via a multilayer coextrusion system. Ecstatically, a regular and symmetrical transcrystallinity (TC) structure with abundant β-form crystals was constructed in iPP layers. Noticeably, the crystallization of cPP required a lower supercooling degree and the crystallization rate of cPP was faster than that of iPP. Accordingly, before iPP layers crystallized, numerous α-form crystals emerged at the interfaces within cPP layers, which could act as α-row nuclei. Under rapid cooling, closely packed β-nuclei were induced near the interfaces via an α-to-β transition, thereby facilitating the emergence of β-form TC. Furthermore, by increasing layer numbers, the crystalline morphologies in iPP layers varied from a sandwich structure of TC/α-form spherulites/TC to a two symmetrical TC structure. Such a unique structure of a two symmetrical TC structure with abundant β-phase may not only alleviate the stress concentration and cavitation caused by the existence of spherulites, but also increase the relative proportion of β-form crystals in iPP layers, leading to the remarkable enhancement of strength and toughness. Therefore, this work provided an additive-free method to fabricate high-performance iPP products by constructing a continuous β-TC structure.