Improving adhesion between acrylonitrile-butadiene rubber and glass fiber cord by covalent bonding and secondary polar interactions

Adhesion promoting systems based on 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, hexamethylenetetramine, m-aminophenol, and silica were added into acrylonitrile-butadiene rubber (NBR) compounds to facilitate improved adhesion to a glass fiber cord. The kinetics of sulfur vulcanization, static and dynamic mechanical properties, surface energy, and adhesion to a glass fiber cord of the rubber compounds were studied. The addition of the adhesion promoters significantly influenced compounds' vulcanization, which resulted in significantly changed mechanical properties of the vulcanizates, while the dynamic properties were impacted only slightly. The surface energy measurement results were not in line with the final adhesion test results, which were most likely caused by the effect of acrylonitrile monomer units of NBR orientation toward the bulk of the compound. In consequence, the results indicated a lowering of the surface energy of the samples containing the adhesion promoters, whereas the pull-out test of the glass cord showed a significant improvement of the compounds' adhesion. The most effective adhesion-promoting system consisted of hexamethylenetetramine, m-aminophenol, and silica resulting in an over 300% increase of the adhesion force in comparison to unmodified NBR.