Stabilization Mechanism of Micropore in High-Density Polyethylene: A Comparison between Thermal and Mechanical Pathways

Aiming to reveal the stabilization mechanism of micropore embryos formed during cold stretching in high-density polyethylene films, samples are subsequently subjected to temperature elevation and strain holding at 25 degrees C, respectively. The corresponding structure evolution is tracked. It is found that after strain holding at 25 degrees C and subsequent strain recovery, inhomogeneously distributed cavities are produced, most of which can be healed as temperature is elevated to 110 degrees C. Consequently, only a small number of nonevenly distributed micropores are formed during the subsequent hot stretching. While for thermal pathway, micropores and fibrils can be formed as temperature is elevated. The hot stretching membrane exhibits uniformly distributed micropores and the micropores are well interconnected, indicating that micropores stabilized via temperature elevation are permanent and homogeneous. The results reveal different stabilization mechanisms of micropores via the thermal and mechanical pathways with regard to the distribution as well as the amount of permanent micropores.