Structure–Property Relationships in Linear Polyethylene: Effects of Phase Composition on Tensile Behavior, Post‐Yield Necking and Strain Hardening

This study explores the effects of polymer phase composition, molecular weight (MW) and molecular weight distribution (MWD) on the tensile properties of linear polyethylene (PE) resins. Uniaxial tensile testing under quasi‐static loading conditions was conducted to establish the relationship between processing, structure and properties in linear PE samples with standard phase composition (SPC) and inverted phase composition (IPC). Solid‐state nuclear magnetic resonance (SS‐NMR) and wide‐angle X‐ray scattering (WAXS) were employed to perform both quantitative and qualitative analyses of crystalline, non‐crystalline, and interfacial contents post‐necking strain hardened specimens. All studied samples exhibited stable necking but only IPC‐PE samples experienced post‐necking strain hardening, which is associated with a higher presence of metastable crystalline species (monoclinic crystalline phase) and more stable interfacial content. In contrast, SPC‐PE samples showed increased interfacial content formation upon tensile deformation but did not exhibit post‐necking strain hardening behaviors. The necked region of all samples exhibited higher crystallinity than the control region, driven by the transformation from non‐crystalline to crystalline phases under uniaxial tensile stress. These findings highlighted the crucial role of molecular organization and phase morphology in optimizing the mechanical performance of linear PE resins.