Structural evolution and performance modification mechanism of electron beam irradiation cross-linked polyethylene-based packaging films

To address the performance limitations of polyethylene (PE)-based packaging films, this study systematically investigated electron-beam irradiation modification of five commercial PE grades. These limitations encompass inadequate mechanical properties, a narrow heat-sealing window, poor barrier stability, and a poorly understood irradiation mechanism. The five grades are two low-density polyethylenes (LDPE), one linear low-density polyethylene (LLDPE), one medium-density polyethylene (MDPE), and one metallocene-catalyzed linear low-density polyethylene (mLLDPE), irradiated at 0, 80, 120, 160, and 200 kGy. Branched LDPE was effectively crosslinked at 80 kGy due to abundant tertiary carbons, whereas linear PEs required >120 kGy for effective crosslinking; all five grades converged to comparable gel content at 200 kGy. The 120–160 kGy optimal dose window synergistically enhanced mechanical strength and heat sealability without compromising optical transmittance or water vapor barrier stability, while a clear oxidative susceptibility hierarchy was established: LDPE > mLLDPE > LLDPE > MDPE. Mechanical property evolution was governed by the competition between crosslinking-induced reinforcement (dominant in low-crystallinity LDPE and mLLDPE) and crystallinity disruption (which prevailed in high-crystallinity LLDPE and MDPE), with elongation at break decreasing continuously across all grades due to crosslinking constraints on chain mobility. Comprehensive structural analyses confirmed that while the PE backbone remained intact, significant microstructural modifications (including crosslinking network formation, crystallite refinement, reduced crystallinity, and limited oxidation) collectively determined the macroscopic property evolution. This work establishes a robust irradiation regulation system that resolves dose imbalance and material adaptability issues, elucidates the intrinsic structure-dose-performance relationship of polyethylene films, and provides a theoretical foundation and practical guidance for the precise property tailoring and high-value application of irradiation-modified recyclable packaging materials.