Competing Chain Scission and Cross‐Linking Pathways in Electron‐Beam‐Irradiated LDPE and EVA : A Spectroscopic–Thermomechanical–Network Analysis

ABSTRACT Electron‐beam (EB) irradiation of polyolefins is often treated as a monotonic cross‐linking process, despite evidence of degradation at high doses. In this study, the competing effects of cross‐linking and chain scission in low‐density polyethylene (LDPE) and ethylene–vinyl acetate (EVA) were investigated over 0–250 kGy using combined spectroscopic and thermomechanical analyses. Fourier‐transform infrared spectroscopy and X‐ray photoelectron spectroscopy were used to monitor chemical evolution, while gel content, dynamic mechanical analysis, and thermogravimetric kinetics were used to evaluate network structure and thermal stability. The results indicate three dose‐dependent regimes: a radical‐limited regime at low doses, a cross‐link‐dominated regime at intermediate doses, and a scission‐dominated regime at high doses. Maximum thermal stability occurred near the intermediate regime, with activation energy increasing by approximately 20%–25%. EVA exhibited earlier network formation and higher cross‐link density than LDPE due to enhanced radical stabilization. These findings suggest that network topology governs degradation behavior and provides a basis for optimizing irradiation conditions in semicrystalline polyolefins.