Adhesion of Vulcanized Rubber Surfaces: Characterization of Unmodified and Electron Beam Modified EPDM Surfaces and Their Co-vulcanization with Natural Rubber

Abstract

Peel adhesion behavior of unmodified and modified ethylene propylene diene methylene (EPDM) vulcanizates covulcanized with gum natural rubber (NR) is reported in this paper. Modification of the vulcanizate surface has been carried out by electron beam (EB) irradiation with or without EB sensitizers such as trimethylol propane triacrylate (TMPTA) and tripropylene glycol diacrylate (TPGDA). The doses of both EB and TMPTA/TPGDA have been varied in separate experiments keeping one of them constant. The surface features have been analyzed using several analytical techniques like attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray sulphur mapping, surface energy measurements, free sulphur and gel content analysis. In comparison to its unmodified EPDM vulcanizate counterpart, 100 kGy modified EPDM vulcanizate in presence of 10 wt% TMPTA shows a maximum increase in O/C ratio value from 0.01 to 0.14. High energy irradiation leads to oxidation, grafting, breakdown of cross-links and blooming, which have been quantified. The joint strength of the modified and unmodified vulcanized EPDMs with gum NR has been tested at room temperature and is found to be a strong function of the nature and extent of the modification and surface roughness. The 10 wt% TMPTA soaked EPDM vulcanizate irradiated at 100 kGy has shown the highest peel strength (71% over that of the untreated sample) among all the samples.