(540c) Structure-Property Relationships in Crosslinked EVA Elastomers

Ethylene-vinyl acetate (EVA) is a commodity-scale polymer frequently used as a crosslinked elastomer where durability in a range of environmental conditions is required. Perhaps the most widely known application involves the incorporation of crosslinked EVA foam into running shoes where it is subjected to countless cycles of high impact compression followed by recovery. Crosslinked EVA is also used as a protective film for solar cells where it must not only withstand prolonged exposure to UV radiation but also any potential inclement weather. Outside of these two specific applications, crosslinked EVA is also frequently used as the primary material for seals and gaskets across a range of industries where properties like chemical and creep resistance start to play a crucial role in material selection.

While crosslinked EVA is used in a range of ubiquitous applications, there is still a gap in the fundamental understanding of how the structure of an EVA polymer contributes to the end-use properties of the crosslinked or crosslinked and foamed material. This gap becomes particularly important as the chemical industry looks for ways to make these materials more sustainable, either by utilizing bio-based monomers, decreasing the energy utilization of the process technologies used to synthesize the polymers, or by incorporating dynamic crosslinks into the material to improve recyclability. The macroscopic mechanical properties of non-crosslinked EVA materials are related not only to the amount of vinyl acetate incorporated along the ethylene backbone, but also the molecular weight and chain topology of the resultant EVA polymer. All these interdependent factors influence the crystallinity of the final material. The addition of crosslinks further influences the material crystallinity and overall density of effective crosslinks such that it is possible to tune the behavior of a crosslinked EVA elastomer via control of VA content, molecular weight, and chain topology. Understanding the interplay between all of these effects not only enables better material selection and property adjustment to meet current application requirements but also provides a roadmap for future, more sustainable materials development.