Influence of morpho-structural parameters on environmental stress cracking in polyethylene

Polyethylene (PE) is widely utilized in several industries due to its versatility and mechanical strength, yet its long-term performance is often hindered by slow crack growth (SCG) and environmental stress cracking (ESC). This study quantitatively evaluates the influence of key morpho-structural parameters on SCG and ESC resistance in PE, using a linear elastic fracture mechanics (LEFM) approach to assess the effect of different comonomers on fracture toughness. Four PE materials were analyzed: two medium molecular weight, linear low-density polyethylenes (LLDPE) co-polymerized with 1-butene (Material A) and 1-hexene (Material B); a high molecular weight LLDPE copolymerized with 1-hexene (Material C); and a medium molecular weight, high-density polyethylene (HDPE) homopolymer (Material D). The results confirm that molecular weight is a dominant factor in enhancing stress cracking resistance, with the high molecular weight LLDPE (Material C) showing superior performance. Moreover, despite nearly identical structural parameters, Material B exhibited significantly higher SCG and ESC resistance compared to Material A, highlighting the critical role of the commoner type. The research identified three distinct environmental regimes influencing fracture behavior, each dependent on the applied stress intensity factor (K) and material properties. These regimes are: (1) no significant environmental effect at high K values, where fracture is dominated by the material's inherent properties; (2) partial plasticization of craze fibrils at intermediate K values, due to limited diffusion of environmental agents into the crack tip; and (3) full plasticization of craze fibrils at low K values, where extensive diffusion accelerates environmental stress cracking (ESC). By demonstrating how morpho-structural parameters and environmental conditions together influence polyethylene's resistance to SCG and ESC, this study improves our understanding of the underlying mechanisms and underscores the effectiveness of LEFM in evaluating long-term material performance. This knowledge can guide the design with polyethylene materials aimed at improving long-term durability for industrial applications.