Synergistic effects of molecular modalities and biaxial stretching modes on the mechanical and necking behaviour of stretched high-density polyethylene

This study examines the combined effects of molecular modalities (unimodal, bimodal, trimodal) and biaxial stretching modes (sequential and simultaneous) on the yielding, stiffness, and necking behaviour of stretched high-density polyethylene (HDPE).Yield strength and stiffness were examined in relation to oriented material produced by drawing at linear strain rates 5.410 -3 , 2.210 -2 , and 8.610 -2 s -1 under both stretching modes.Simultaneous stretching outperformed sequential stretching, with yield strength increasing with draw rate.Unimodal HDPE showed higher yield strength and stiffness than bimodal and trimodal grades, while trimodal HDPE had the lowest necking tendency from greater flexibility and uniformity.The highest necking tendency was observed in unimodal HDPE in strain localization analysis using the maximum strain/average strain ratio, while trimodal HDPE deformed more uniformly due to improved molecular weight distribution and strain hardening.Increasing the draw rate reduced strain localization, improving mechanical performance.Insights for optimising polyethylene materials in industry are provided by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, and mechanical analyses, establishing the correlation between HDPE structure, processing, and properties.