Adhesion of Styrene-Butadiene Rubbers with Different Silica Content

The influence of silica content of four styrene-butadiene rubbers on their adhesion to polyurethane adhesives was studied. Untreated rubber shows no adhesion due to a weak boundary layer of zinc stearate. Roughening removed zinc stearate from the rubber surface, increased the surface energy and produced surface roughness, so improved adhesion was obtained. The adhesion increased as the silica content in rubber increased, due to an improvement in intrinsic adhesion, and mechanical and physical properties of the rubbers. Chemical surface treatments (halogenation with trichloroisocyanuric acid, treatment with fumaric acid) provided higher adhesion than roughening. In general, chlorination was somewhat more effective than the treatment with fumaric acid, especially in roughened rubbers. Improved adhesion of chemically surface-treated rubbers was due to enhanced mechanical, thermodynamic and chemical adhesion, and to the improved physical, mechanical and viscoelastic properties of rubbers.