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Silicone Adhesives and Primers on Low Surface Energy Plastics and High Strength Metals for Medical Devices

This paper will demonstrate the ability of silicone adhesives, with the aid of primers, flame treatment, or plasma treatment, to adhere to low surface energy plastics and to high strength metals. In general, some plastics are difficult to adhere to because of their low surface energy, available bond sites, and chemical interaction. Most plastic have a surface energy under 50 dynes/cm while aluminum, an easier substrate to adhere to, is closer to 825 dynes/cm. Surface energy is a thermodynamic effect of how a liquid will ‘wet out’ on a surface. Low surface energy materials, like plastics, do not allow a liquid, like an adhesive, to ‘wet out’ on its surface. Adhesion chemistry tells us that the better an adhesive can ‘wet out’ on a substrate, the more surface area it can cover and allow more reactive groups to bond, making a stronger bond. Several low surface energy plastics and high strength metals were tested with silicone adhesives and primers, as well as with plasma treatment, to achieve cohesive bond failure when performing lap-shear testing. This list of substrates evaluated include polycarbonate, polyetherimide, polyamide, polyurethane, polymethylmethacrylate, polysulphone, titanium, stainless steel, and aluminum.