Work

Dynamic Crosslinking for EVA Recycling

Year: 2024

Type: book-chapter

Abstract: Covalently crosslinked polyethylene vinyl acetate (EVA) networks provide a balance of processing performance, mechanical properties, and durability that make these materials the ideal selection for some high-performance, high-volume applications. Foams produced from crosslinked EVA are the material of choice for shoe midsoles, including technically advanced athletic shoes. However, the same characteristics that make permanent networks such excellent candidates in materials selection processes also represent a difficult environmental challenge. Once formed, these network structures do not melt, flow, or dissolve to enable the use of conventional reprocessing or recycling methods. As a result, most crosslinked polymer networks accumulate as plastic waste. The most significant technical barrier to recycling crosslinked polymer networks is the permanent nature of the covalent bonds that hold them together. In this paper, we demonstrate that covalently crosslinked networks can be converted to dynamic exchangeable networks called vitrimers. These vitrimer networks can undergo topological rearrangements that enable melt re-processing. Crosslinked EVA is converted to a vitrimer via a mechanochemical approach using a catalyst that promotes a transesterification reaction. The vitrimerized EVA can then be reprocessed at moderately low temperatures via compression molding without loss in the mechanical properties. Thus, the vitrimerized particles can be recycled as secondary feedstock for new, value-added products.

Source: Wiley eBooks

DOI: 10.1002/9781394214297.ch31