Degradation of Rubber-to-Metal Bonds During Simulated Cathodic Delamination

Cathodic delamination of neoprene-to-steel adhesive bonds prepared using a proprietary vulcanizing adhesive and primer was investigated using Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Chlorinated rubber in the adhesive and primer was stable during immersion in NaOH solutions simulating the high pH conditions obtained at the bondline during cathodic delamination. However, methylene groups linking phenol moieties in phenolic resins in the primer were rapidly oxidized during immersion in NaOH solutions to form benzophenone linkages which were oxidized further to carboxylic acids and quinones. Chlorine produced by dehydrohalogenation of chlorinated rubber in the adhesive and primer during curing of the neoprene reacted with ZnO in the primer to form ZnCl2 in the bondline. Failure of adhesive bonds between neoprene and steel during cathodic delamination is probably related to oxidation of the phenolic resins in the primer and to osmotic effects related ...