Effects of post-treatment of meta-aramid nanofiber mats on the adhesion strength of epoxy adhesive joints

The mismatch in the coefficient of thermal expansion (CTE) between adherends and adhesives is one of the main reasons for the fracture and failure of adhesive bonding structures. Therefore, the adhesive layer requires reinforcing materials, which can reduce the CTE, enhance the reliability of the adhesive joints and improve the mechanical strength. In this work, electrospun meta-aramid nanofiber mats with a high specific strength and low CTE were used to reinforce the epoxy adhesive. Microwave treatment was introduced to improve the adhesion strength by enhancing the mechanical strength of the nanofiber mat. The surface morphology and fiber orientation of the nanofiber mats with respect to the microwave irradiation time were investigated using scanning electron microscopy (SEM). The residual solvent in the microwave-treated nanofiber mats was monitored via thermogravimetric analysis (TGA). Plasma treatment was conducted to functionalize the microwave-irradiated nanofiber mats with epoxy adhesive to improve the interfacial strength. The characteristics of the plasma-treated nanofiber mats were investigated using X-ray photoelectron spectroscopy (XPS). Thermo mechanical analysis (TMA) confirmed that the CTE of the post-treated meta-aramid nanofiber mat toughened the epoxy adhesive. The stress and strain distribution after the curing and during tensile testing of the single-lap joint were calculated by using finite element analysis (FEA). Single-lap tests were performed to estimate the effect of the reinforcing materials on the adhesion strength. As a result, the post-treated meta-aramid nanofiber mats exhibited an effectively reduced CTE of the adhesive layer and increased adhesion strength.