Recyclable ethylene-vinyl acetate copolymer vitrimer foams

Current practices in the production and disposal of polymers follow an unsustainable trend. Foamed ethylene-vinyl acetate copolymer (EVA) is no exception as chemical cross-linking limits recyclability. Here, we demonstrate that we can readily control the kinetics of the cross-linking networks by changing the usage and variety of linkages with the introduction of reversible transesterification to construct EVA vitrimer. EVA vitrimer foams are prepared by physical foaming or chemical foaming. We suggest two strategies for the recycling of EVA vitrimer foams by re-joining and re-foaming. EVA vitrimers could switch states from the bulk vitrimer material to the foam material repeatedly through a re-foaming strategy, and EVA vitrimer foams can be cut-and-reunited through a re-joining approach. The change in the mechanical properties of the recycled vitrimer foams proves the importance of the reaction kinetics of dynamic covalent chemistry. These findings will stimulate further sustainable developments in the designing and recycling of polymeric foams.