Adhesion loss at epoxy/glass interfaces under hygrothermal conditions

The adhesion loss at epoxy/glass interfaces under hygrothermal conditions was investigated. One thermal cured model epoxy system and one UV cured developmental epoxy system were used in this study. Several factors that could affect the adhesive strength of the epoxy/glass joints were evaluated to get a better understanding of adhesion loss of adhesive joints under hygrothermal conditions. A model was proposed to predict/calculate the adhesion loss at the epoxy/glass interface for this experimental adhesive.; The effect of surface treatment of the substrate on adhesion loss was studies. Two coating procedures were used: (1) a monosilane and dipodal mixture, or (2) dipodal-then-monosilane two-step process. The results were compared with the adhesion strength by a monosilane treatment. It was found that the mixture of dipodal silane coupling agent and monosilane resulted in poor adhesion between epoxy and glass substrate.; For a two-step treatment, BTSE and GPS are selected for the investigation and it offers better moisture resistance for the model epoxy systems than bare glass surface or GPS treated glass surface. The rate of adhesion loss of those adhesive joints is slower than GPS treated surface or bare glass. However, for a longer time, when the adhesion drops to a plateau region, the adhesive joint by two-step treatment does not show significantly better adhesion than GPS treated surface or the bare glass surface.; XPS is used to investigate the locus of failure. It was found that the failure mode for BTSE/GPS coated surface is cohesive failure when the specimen is dry. The fracture surface is within epoxy bulk. After hygrothermal aging, the failure mode is adhesive failure.; A model is proposed to predict adhesion loss based on the area of cohesive failure and adhesive failure on a commercial UV cured epoxy. The predicted values of adhesion by the model fit well with the experimental data. SEM is used to obtain the images of fracture surfaces.