Cathodic Debonding of Neoprene from Steel

X-ray photoelectron spectroscopy (XPS) has been used to determine the failure mechanisms in neoprene/steel adhesive bonds during cathodic delamination or during immersion in aqueous solutions of NaOH to simulate the effects of cathodic delamination at the bondline. Delamination of the rubber from substrates that had been pretreated by acid-etching began at the edges of the bonds and proceeded slowly inward. The centers of the bonds were always intact except for every long times when complete delamination of the rubber was observed. Failure was near the primer/oxide interface but with islands of rubber remaining on the substrate and islands of oxide remaining on the rubber. The failure mechanism was associated with degradation of the phenolic primer and with dehydrohalogenation of chlorinated rubber in the adhesive and primer. Dehydrohalogenation resulted in the formation of inorganic salts which could dissolve during exposure to water at high pH values, leading to large osmotic pressures at the i...