Changes in the structure and physical properties of acrylic and epoxy adhesives in response to high-temperature and high-humidity environments

The strength of adhesives and adhesive joints degrade due to changes occurring in terms of environmental heat, moisture, and temperature conditions experienced during use. Adhesives with a sea-island phase separated structure consisting of hard and soft domains, are designed to improve reliability when it comes to adhesion. In this study, we investigated the changes occurring in terms of in adhesive strength and phase separated structures during the processes of repeated moisture absorption and desorption for two commercially available adhesives. We measured the adhesive strength of epoxy and acrylic adhesives containing elastomers during dry/wet cycles. The collapse of the phase-separated structures was confirmed via TEM and AFM-IR observations. The changes seen in terms of the continuous structure of the rubbery phase in the acrylic adhesive was greater than that seen in the epoxy adhesive. This caused delamination at the interface located between the adherend and the adhesive. Thus, the adhesive strength of epoxy adhesive has been deemed stable in relation to changes occurring in terms of temperature and humidity. •The strength of adhesive joints degrades mainly due to heat and moisture.•The effect of water absorbance was found out using epoxy and acrylic adhesives.•The collapse of the phase-separated structures was confirmed via TEM and AFM-IR.•The rubber phase change could affect physical properties of adhesives after test.