Mechanism of improved aged rubber-to-brass adhesion using one-component resins

Using a squalene liquid rubber modeling approach, we have shown recently that the role of an adhesion promoting one-component resin system is similar to the conventional resorcinol based two-component resin system(1). However, to further study the effect of resins in real natural rubber based formulations, eight similar formulations were mixed to make compounds in natural rubber. These rubber compounds were characterized and tested for their mechanical properties viz. stress at break, stress at 300% strain, elongation %, initial, heat and humidity aged wire adhesion pull-out test, tensile tear strength test. Furthermore, to confirm our proposed theory of the migration of resins from the rubber matrix towards the surface, the surfaces of the rubber compounds were studied using ATR-FTIR spectroscopy. NMR spectroscopy was performed on the rubber compounds to study the sulfur crosslink density distribution. Based oil our new findings relating to improved corrosion performance of sulfidized brass cords a theory has been put forward that loss of rubber-to-brass adhesion is in fact due to the aging of the brass cord. This aging of brass cord is found to be clue to the dissolution of iron from the steel cord. It was observed that the use of different formulations affected the corrosion performance of the sulfidized brass cords in a different manner. The use of resins, particularly one-component resins, seemed to inhibit this iron dissolution thus resulting in durable rubber-to-brass adhesion even in the humidity aged adhesion blocks.