Adhesion in EPDM joints: Role of the interdiffusion mechanism on interfacial co-crosslinking

The purpose of this study was to understand the relationship between the me chanism of interdiffusion of the polymer chains across the interface and th e formation of crosslinks in the interfacial zone when two elastomer sheets are joined and crosslinked. It is commonly accepted that the strength of t he interface thus obtained is related to the number of interlinks that are created in the molecular interphase. This number generally is considered as equal to the number of crosslinks determined in the bulk. Ethylene-copropy lene-codiene polymer (EPDM) does not follow this general law. The slow diff usion of the chains at the interface may be responsible for the peculiar be havior observed. In order to separate the two mechanisms responsible for th e interfacial strength, diffusion, and crosslinking, two crosslinking proce dures, namely peroxide crosslinking at high temperature and electron beam c rosslinking at room temperature, have been used. This latter procedure allo ws control of the diffusion depth. It has been shown that diffusion of EPDM chains is indeed occurring at a much Slower rate than expected, leading to less efficient co-crosslinking in the interfacial zone. (C) 2000 John Wile y & Sons, Inc.