FUMARIC-ACID AS A PROMOTER OF ADHESION IN VULCANIZED SYNTHETIC RUBBERS

The addition of dicarboxylic acids to polyurethane adhesives, to impro ve their adhesion to vulcanized synthetic rubbers, may cause the degra dation over time of the adhesives. To avoid the degradation of polyure thane adhesives, this study proposes a surface treatment on vulcanized synthetic rubbers with carboxylic acid solutions instead of adding th em to the adhesives. In all the styrene-butadiene rubbers studied, a g reat improvement in adhesion to polyurethane adhesives has been obtain ed. The nature of the solvent used to disperse the fumaric acid over t he surface, as well as the nature of the rubber, determined the effect iveness of the surface treatment. The use of fumaric acid solutions pr ovided optimum results when the surface of the rubber was slightly rou ghened. The increase in the adhesion properties of styrene-butadiene r ubbers, treated with fumaric acid, has been attributed to an increase in the degree of the surface roughness and to an enhancement in the su rface energy (due to the elimination of abhesive substances on the sur face of the rubber and to the formation of C-O groups by surface oxida tion). The effectiveness of the surface treatment on rubbers with fuma ric acid in the adhesion of styrene-butadiene rubbers has been compare d with those produced by other common treatments, such as halogenation and roughening. In general, T-peel strengths obtained in the rubbers treated with fumaric acid were similar to those obtained through halog enation and were always higher than those obtained through roughening. Therefore, surface treatment of styrene-butadiene rubbers with fumari c acid can be considered as an alternative method to chemical treatmen ts currently used, especially in the footwear industry.