Effect of UV irradiation on epoxy adhesives and adhesively bonded joints reinforced with BN and B4C nanoparticles

Abstract

The effect of environmental conditions on epoxy polymers restricts their usage in outdoor applications. Although many studies of epoxy adhesive and adhesively bonded joints under different environmental conditions such as saltwater, acid environment, and high temperature have been carried out, the effect of ultraviolet (UV) irradiation has not been examined to date in detail. The primary focus of this research is to improve the usage limitations and reduce the degradation due to UV irradiation by incorporating boron nanoparticles into epoxy resin. Epoxy adhesives were reinforced with 2% by weight functionalized boron nitride (BN) and carbide (B4C) nanoparticles in accordance with this purpose. Bulk adhesives and adhesively bonded aluminium joint specimens were produced with unreinforced and boron nanoparticles reinforced adhesives. Subsequently, produced specimens (bulk adhesives and adhesively bonded joints) were subjected to 480, 960, and 1440 h of continuous UV irradiation chamber and characterized to specify the effects of boron nanoparticles on the degradation. The changes and degradations caused by UV irradiation on bulk epoxy adhesives were determined by FT-IR, SEM, DSC, DMA, and tensile test techniques. Similarly, the static tensile test was applied to determine the effect of UV irradiation on adhesively bonded joints. When the experimental results obtained from the research were examined, it was observed that the bulk adhesives and adhesively bonded joints degraded under UV irradiation depending on the UV exposure time. However, the degradation rate was decreased by the nanoparticle reinforcement to the epoxy adhesive. The glass transition temperature values of the adhesives increased depending on the exposure time in line with the temperature effect of the environment. Accordingly, while the elasticity modulus and storage modulus of the adhesives increased, their tensile strengths showed a decreasing trend depending on the exposure time to UV irradiation. Similarly, the adhesively bonded joints showed a decrease in failure load at the end of 480, 960, and 1440 h due to the thermal effect rather than UV rays. The degradation behaviour observed in mechanical properties was obtained at higher rates in unreinforced specimens.