Adhesion to Plasma-Modified LaRC-TPI II. Effect of Plasma Treatment on Peel Strength

LaRC-TPI, an aromatic thermoplastic polyimide, was exposed to oxygen, argon and ammonia plasmas as pretreatments for adhesive bonding. A 180[ddot] peel test with an acrylate-based pressure sensitive adhesive tape as an adherend was utilized to study the interactions of the plasma-treated polyimide surface with another polymeric material. The peel strengths of the pressure sensitive adhesive tape on the plasma-treated LaRC-TPI fell below the level of the non-treated controls, regardless of the plasma treatment used. Failure surface analysis by XPS revealed the presence of polyimide on the pressure sensitive adhesive failure surface, indicating failure in the plane of a weak boundary layer created by plasma treatment. The removal of the weak boundary layer by a solvent rinse restored the peel strength to the level of the control. Comparison with tape adhesion peel strengths of oxygen plasma-treated high density polyethylene showed that the physical condition of a polymer surface following plasma treatment plays an important role in determining the level of adhesion which can be achieved.