Customized Multimodal Cellular Elastomer Foams through Presetting Cells before CO₂ Foaming

Elastomer foams with customized multimodal cellular structures have great application requirements in advanced fields, but a simple and practical way to realize it needs to be further studied. Herein, a strategy of presetting cells into elastomers before supercritical CO₂ foaming was introduced to customize the cellular structures. Typically, taking olefin block copolymers (OBC, a thermoplastic elastomer with crystalline hard segments and rubbery soft segments) foams as an example, bimodal, sandwich, and gradient multimodal cellular structures were successfully prepared. The interaction between preset cells and newly nucleated cells during foaming had been systematically studied by controlling the morphology of preset cells and foaming conditions. It was found that the configuration of preset cells and the nucleation rate of small cells in OBC foams had a significant impact on their cellular structures. Specifically, the bimodal cellular structures can improve the expansion ratio and elasticity of OBC foams, and their rebounding ability could be improved by 14%, while their energy loss coefficient would be decreased by 17% (compared to homogeneous ones in this study). Furthermore, the feasibilities of this strategy in other elastomer foams (like POE, EPDM, and EVA foams) with bimodal cellular structures were also verified, which was expected to promote the development of high-performance elastomer foams.