Effects of Surface Treatment with Plasma on Adhesive Strengths at Cryogenic Temperature

The variations of adhesive strength at cryogenic temperature of epoxy to polyimide (PI) or polyethylene (PE) films, which were exposed in plasma composed of one of nitrogen, argon and oxygen, were studied for the simulation of the interface strength between polymeric fibers and resins of advanced composite materials. Plasma surface treatments for polymeric films were performed aiming at increasing surface energy without spoiling bulk properties of films. ECR (electron cyclotron resonance) was employed for production of plasmas and its characteristics was evaluated. The results indicated that surface energies of films increased when the films were deposited to plasma. A film-resinfilm lap test were also carried out. In the case of untreated PE films, debonding at film-resin interface arised on cooling down process to cryogenic temperatures. On the other hand, in the case of plasma treated films, debonding was not induced in cooling down process. Adhesive strength between film and resin was improved by ECR plasma processing for a few ten seconds' exposure. Surface analysis revealed that the introduction of polar groups induced the improvement. The plasma treatment was found to be applicable to the organic fibers.