Tailoring the Properties of Natural Eucommia Rubber Foams: A Comparative Study of Sulfur and Peroxide DCP Vulcanization Systems

Eucommia rubber (ER) foam is a unique bio-based material that combines a porous foam structure with crystalline and crosslinked networks. Nevertheless, the interplay between vulcanization/crosslinking and foaming processes in ER remains insufficiently explored. In this study, two representative vulcanization systems, namely sulfur and dicumyl peroxide (DCP), were innovatively employed to fabricate Eucommia rubber (ER) foams. For the first time, this work systematically examines the effects of crosslinking agent type and content on the foaming behavior, mechanical properties, and micromorphology of ER foams. The primary scientific objective is to establish the structure–property relationship between the vulcanization system and the foaming kinetics of ER. Detailed experimental results reveal that under optimized conditions (0.8 phr sulfur and 0.4 phr DCP [parts per hundred parts of rubber by weight]), the ER foams exhibit optimal foaming ratios of 639% and 748%, respectively, demonstrating outstanding foaming capability. Sulfur-cured foams possess a notably higher proportion of open-cell structures and remarkable shape memory properties. These findings demonstrate the critical role of the crosslinking system in regulating the structure and performance of ER foams, highlighting their potential for use in advanced areas such as biomedical, damping, and separation materials.