Simultaneously achieving self-toughening and self-reinforcing of polyethylene on an industrial scale using volume-pulsation injection molding

Abstract

It is critical and difficult for production of large polymer parts using injection molding method to simultaneously achieve both good flowability and mechanical properties. Volume-Pulsation Injection Molding (VPIM) technology, exerting a high-amplitude vibration force field during the entire injection molding process, can be exploited to address this challenge, on an industrial scale. Through orientation of macromolecules with vibration forces during injection molding, mechanical properties of polymers can be improved at low cost without sacrificing flowability. In this study, employing VPIM technology, self-toughening and self-reinforcing of high-density polyethylene (HDPE) were realized while maintaining satisfactory flowability. Comparing with those of the convention injection molding (CIM) samples @ 210 °C, impact and yield strengths of the VPIM samples @ 0.7 Hz-210 °C were increased by 782.93% and 14.25%, respectively. According to crystal morphologies, shish-kebabs were formed in intermediate layer, leading to a remarkable enhancement in mechanical properties. Injection temperature and processing frequency had an influence on the shish-kebab structure and the intermediate layer thickness, thereby determining mechanical properties. These analysis results were supported by the evidence from impact-fractured surface morphology, 2D-SAXS, 2D-WAXD, and DSC. The response law of crystal structure and morphology to the vibration flow field was proposed to uncover the influence of processing conditions on material properties.