Surface plasma treatment effect on shear strength in adhesively bonded joints with modified addition curing silicone adhesive

Strong single lap bonded joints of different materials are of great importance in various advanced industries. Silicones are commonly used as reliable adhesives for this purpose. Although silicones offer excellent properties such as resistance to extreme temperatures and weather conditions, as well as flexibility, their low surface energy limits their application as adhesives. To address this issue, we added a hydrogen-containing silicone adhesion promoter to an addition-curing silicone adhesive. We also introduced functional groups on the aluminum and glass adherends through air plasma (AP) surface treatment. These modifications were made to improve the interface between the adhesive and the adherend. We also added hydrophobic fumed silica to the adhesive formulation to enhance its overall bond strength and toughness. The single lap-shear tests were carried out to study the lap-shear strength (LSS) of the adhesively bonded joints. It was shown that the presence of the adhesion promoter on AP-treated adherends results in a minimum increase of 196 % in LSS. It was observed that the adhesion promoter has a plasticizing effect in the absence of AP treatment, resulting in poor mechanical strength of the joints. Fumed silica has been shown to significantly impact the LSS of aluminum and glass adherends, increasing it by a factor of 3 and 4, respectively, at the concentration of 5 phr. In all cases, glass specimens exhibited stronger bonds.