Fundamental Influences of Crosslinking Structure on the Cell Morphology, Creep Property, Thermal Property, and Recycling Behavior of Microcellular EPDM Foams Blown with Compressed CO₂

Abstract

In this study, the crosslinked ethylene–propylene–diene monomer (EPDM) foams were prepared by batch foaming using compressed CO2 as the blowing agent. The various crosslinking structures, i.e., the local primary crosslinking structure, the micro-crosslinking structure, and the full crosslinking structure, were generated by adjusting the loading of the crosslinking agent. The models were established to illustrate the fundamental influences of crosslinking structures on the evolution of cell morphology. EPDM-0.2B with 0.2 parts per hundred of rubber (phr) loading of the crosslinking agent had the micro-crosslinking structure, which improved the foamability of EPDM significantly. The foaming temperature window was broadened from 40–80 to 100–200 °C, and the expansion ratio was increased from 5.6 to 7.1 compared with pure EPDM. Meanwhile, the structure endows the EPDM-0.2B foam with improved creep resistance, increased thermal stability, and a melt-recycling ability. The EPDM foam with the full crosslinking structure exhibited better creep resistance and thermal stability, but the structure spoiled its melt-recycling ability significantly.