Crystallization of polypropylene in multilayered spaces: Controllable morphologies and properties

Abstract

In this work, multilayer materials containing alternating layers of polypropylene (PP) and ethylene vinyl acetate copolymer (EVA) were fabricated through layer-assembly coextrusion. With increasing the number of layers, the growth of spherulites distributed in PP layers was gradually confined along the thickness direction leading to the slowdown of crystallization rate. Owing to the formation of the anisotropic spherulitic morphology, its influence on mechanical and optical behaviors of the multilayer specimens was investigated, respectively. Results revealed that the layer multiplication induced the increase of yielding strength and promoted the propagation of necking zone in a stretching process. When a beam of light passed through the specimen with more layers, a higher transmittance could be directly collected along the incident direction. It was recognized that the confined spherulites with high aspect ratios played a crucial role in weakening the light deflection, which provided a potential route to massively fabricate the transparent PP without filling nucleating agents.