Reactive crosslinking-charring integrated EVA composites with suppressed flame-retardant migration

Long-term exposure to outdoor environments inevitably induces the aging of polymers and the migration of flame retardants, which severely deteriorates the flame retardancy and mechanical durability of composites. Herein, a reactive crosslinking-charring integration strategy is proposed by incorporating octavinyl polyhedral oligomeric silsesquioxane (OVPOSS) as a dual-functional crosslinker and char-forming synergist into ethylene-vinyl acetate (EVA)/aluminum hydroxide (ATH) systems. Through initiator-assisted covalent crosslinking, a highly crosslinked EVA network (CLEVA-OVPOSS/ATH) featuring Si-O-C hybrid architectures is constructed, as confirmed by gel content analysis and Fourier transform infrared spectroscopy. This structural design fundamentally suppresses flame-retardant migration while effectively overcoming the conventional trade-off between mechanical properties and flame retardancy. Compared with neat EVA, the resulting composite exhibits a 100 s delay in time to ignition, an 83.1 % reduction in peak heat release rate, and a markedly enhanced fire performance index of 0.88 m²·s·kW⁻¹. More importantly, the dense crosslinked network coupled with silicon-induced char densification endows the composite with exceptional water resistance and long-term fire safety stability under harsh environments. These findings establish a new design paradigm for durable flame-retardant EVA materials and provide mechanistic insights into migration-resistant polymer systems for advanced outdoor applications such as photovoltaic encapsulation, cable insulation, and electronic packaging.