Tracer study of kinetics and mechanism of hydrolytically induced interfacial failure

Abstract

Abstract Analysis of the kinetics of hydrolytic desorption of chemisorbed C‐14 labelled polymeric APS (gamma‐aminopropyltriethoxysilane, a coupling agent for glass reinforced epoxy resins) from flat silica or borosilicate surfaces, indicated that the polymer probably consisted of short chains each chemisorbed at one end to the surface with little or no cross‐linking. A method was developed to determine from kinetic data whether or not more than one type of bond is severed during the desorption process. Application of the method to these results indicated that more than one type of linkage was being hydrolyzed in the desorption of APS. Glass‐epoxy adhesive joints were prepared from glass containing various amounts of APS chemisorbed to the surface. In one set of experiments, the amounts were varied through aqueous extraction of increments of the originally deposited material. In a second set, the amounts were varied by adsorption from very dilute solution. The lifetimes of the adhesive joints were measured under static load in hot water. It was found that the maximum lifetime is not dependent on the thickness of the chemisorbed layer, but that it is dependent on the lateral surface concentration of the chemisorbed polymeric units. Examination of the debonded joints for radioactivity indicated that failure resulted from hydrolysis of siloxane bonds in the coupling agent structure.