Electron-beam crosslinking of flame-retardant LDPE/EVA composites: Effects of metal hydroxides and zinc borate on fire and mechanical performance

Electron-beam (EB) irradiation provides an initiator-free route for modifying highly filled polymer systems, but the combined influence of radiation-induced network formation and halogen-free flame-retardant formulation remains insufficiently understood. This study investigates dose-dependent EB effects on LDPE/EVA composites containing aluminum trihydroxide (ATH), magnesium hydroxide (MH), and zinc borate (ZB) for cable-insulation applications. Composites containing 60–64 wt% inorganic fillers were irradiated at 0–250 kGy and evaluated by gel-content, hot-set, thermogravimetric, tensile, limiting oxygen index (LOI), smoke-density, and cone-calorimetry measurements. Increasing EB dose promoted progressive network formation, evidenced by increased gel content and improved hot-set performance, and was accompanied by enhanced dimensional stability and tensile-strength retention. Fire performance also improved, with LOI increasing from approximately 26%–28% in non-irradiated materials to 31%–34% at higher doses, together with reduced smoke generation and heat release. MH-containing composites generally showed lower smoke-density and heat-release parameters than corresponding ATH-based systems. ZB-containing formulations exhibited further reductions in smoke and heat release and more consolidated post-combustion residues; however, because ZB addition increased total inorganic content from 60 to 64 wt%, these differences cannot be attributed exclusively to an independent ZB effect. Overall, MH/ZB-containing systems at moderate-to-high EB doses showed the most favorable combined network, fire, and mechanical response, demonstrating that absorbed dose and flame-retardant composition act as coupled design variables in highly filled LDPE/EVA composites.