Influence of the Treatment with Sulfuric Acid on Adhesion of Natural Rubber and Cast Polyurethane Elastomers

In this study, natural rubber (NR) was treated with sulfuric acid to improve its adhesion properties to polar polymer. T-peel strength tests, scanning electron microscopy, contact-angle measurement (water), Energy Dispersive X-ray Detector were used to analyze the nature of the NR surface modifications which were carried out with sulfuric acid. A noticeable decrease in contact angle was observed on the rubber surface by contact-angle measurements which can be ascribed to the increase of oxidized moieties on the rubber surface. EDX revealed that oxidized moieties were created through treatment with sulfuric acid. The surface modification and mode of bond failure were studied by scanning electron microscopy (SEM). Immersion in sulfuric acid for 15min produced the maximum adhesion strength (10kN/m) and produced a mixed failure mode (interface & rubber failure in the rubber). Treatment with sulfuric acid produced improved wettability as well as chemical (surface oxidation) and morphological modifications (roughness) of the rubber surface.