SURFACE-ANALYSIS OF DEBONDED CHLORINATED VULCANIZED STYRENE-BUTADIENERUBBER JOINTS

A synthetic vulcanized styrene-butadiene rubber (R) was treated with a halogenation agent (TCI = trichloroisocyanuric acid) to produce impro ved adhesion (i.e. high T-peel strength) in joints prepared with a one -component, solvent-based polyester urethane adhesive. Several amounts (0.5 to 7 wt%) of TCI solutions in ethyl acetate were applied to the rubber surface and, after T-peel tests were carried out, the surfaces of the debonded chlorinated rubber pieces were analyzed with XPS, ATR- infra-red (ATR-IR) spectroscopy, Scanning Electron Microscopy (SEM) co upled with EDX analysis, and contact angle measurements. The T-peel st rength of unchlorinated rubber (0 wt% TCI) joints was small due to the migration of low molecular species (mainly microcrystalline wax) to t he rubber surface during the cure of the adhesive, creating a weak lay er in which the failure was produced. Chlorination with amounts of TCI up to 2 wt% produced a noticeable increase in T-peel strength, but tr eatment with higher amounts of TCI resulted in a decrease in joint str ength. Although chlorination with TCI created chlorinated hydrocarbon groups and C--O moieties on the rubber surface, the surface in contact with the adhesive was additionally degraded and, consequently, the lo cus of failure of the joints varied in a manner which depended on the amount of TCI applied to the surface. Treatment with amounts of TCI up to 2 wt% did not greatly degrade the rubber surface and the mode of f ailure of the joint was mainly interfacial. Chlorination at higher TCI concentration produced a weak chlorinated surface layer which was mec hanically weak, facilitating the failure in this layer during the T-pe el test. The thickness of the chlorinated layer created on the treated rubber is about 5 mu m, and the thickness seemed to be independent of the amount of TCI applied to the rubber surface.