Mass spectrometric analysis of an epoxyphenolic adhesive in the bulk as well as in contact with a metal surface

Abstract

The chemical composition of low-molecular-weight products of polycondensation during the curing of an epoxyphenolic adhesive both in the bulk and in a thin layer in contact with a metal has been studied using pyrolitic mass spectrometry. It was found that the volatile products from the adhesive bulk differed greatly from those released from the thin oligomer layer bordering the metal surface. The difference in chemical composition of the polycondensation products near the metal surface compared with those in the bulk is related to simultaneously occurring thermal desorption of gases from the metal surface. Due to the dissolution of desorption products in the uncured adhesive surface layer, a change is observed in the process of direction of polycondensation and in the chemical composition of the thin subsurface adhesive layer. The greatest effect on the adhesive surface layer structure and properties is exerted by the carbon mono- and di-oxides desorbed from the metal. The metal surface serves as a catalyst for carboxylation and carbonylation taking place near the interface. Thermodesorption of physically and chemically adsorbed molecules and the competing process of solvent absorption by metal structural defects are the possible causes for the onset of microdefects in the epoxyphenolic adhesive layers contacting the metal.