Mechanical robust, recyclable cross-linked EVA foam enabled by dual crosslinking networks

Cross-linked ethylene-vinyl acetate copolymer (EVA) possesses excellent mechanical properties that are widely used in sports and the photovoltaic industry, but it cannot be recycled through melt reprocessing. The emergence of dynamic chemistry provides a viable approach to achieve both high mechanical performance and recyclability in cross-linked EVA. Herein, this study fabricated a dual cross-linked EVA containing covalently cross-linked sites and dynamically cross-linked sites, which improved the mechanical properties and endowed it with reprocessability. The optimal cross-linking network structure was determined, and the bond exchange was clarified through chemical, rheological, and mechanical analysis. The dual cross-linked EVA could be well foamed through supercritical fluid and the foaming temperature was broadened to 180 °C. Low-density and uniform cell structure was obtained for the dual cross-linked EVA foam that exhibited excellent cushioning performance, the peak impact force was reduced from 8081 N to 1281 N, and achieved a superior energy absorption efficiency of 84.1 %. Meanwhile, the dual cross-linked EVA foam could be recycled through a re-foaming strategy. This study demonstrates that incorporating dynamic bonds into the covalent network is beneficial for balancing mechanical properties and recyclability, which provides a valuable insight for designing recyclable and cushioning EVA foam.