Treatment of vulcanized SBR rubber with low-pressure gas plasma using oxygen-nitrogen mixtures

Abstract

Low-pressure gas plasma treatments were proposed as an alternative to the chemical surface treatments (e.g. halogenation, cyclization) of vulcanized styrene-butadiene (SBR) rubber. The effectiveness of low-pressure oxygen plasmas has been already shown. In this study the influence of the oxygen/nitrogen ratio on the adhesion performance of rubber/polyurethane adhesive joints was considered. Different mixtures of oxygen (20–40 vol%) and nitrogen (80–60 vol%) were used for the plasma treatment of an SBR rubber between 1 and 15 minutes, using a power of 50 watts and a residual pressure of 1 Torr. The modifications produced on the rubber surface by the plasma treatment were assessed using advancing and receding contact angle measurements, ATR-IR spectroscopy and scanning electron microscopy. Adhesion was determined from T-peel tests on plasma treated rubber/polyurethane adhesive joints. The treatment of rubber with oxygen-nitrogen mixture plasmas decreased the advancing and receding contact angle values and increased the T-peel strength (a cohesive failure in the rubber was produced). This increase was due to the partial removal of hydrocarbon moieties from the rubber surface and to the creation of oxygen containing species. The increase in the time of treatment decreased the peel strength and made the locus of failure mainly cohesive in the rubber. The higher the percentage of oxygen in the gas mixture, the greater the degree of oxidation on the rubber surface, the higher the degree of roughness and the more effective the treatment. A minimum percentage of 20 % oxygen in the gas composition was required to achieve good adhesion. Nitrogen plasma produced a different effect than the oxygen-nitrogen mixture plasma due to crosslinking reactions on the treated rubber surface which directed the failure to be cohesive in the adhesive.