Brass Powder in Rubber Vulcanizates. The Effect on Adhesion

Brass plating is presently used for promoting the adhesion of rubber to steel cords used in tires. It is generally accepted that the adhesion is due to chemical bonds that are formed between the rubber and brass,1 although evidence has been obtained indicating that the adhesion is the result of a physical phenomenon.2 In addition, a catalytic oxidation theory also has been advanced.1 Natural rubber vulcanizates loaded with brass powder showed an increase in crosslinking (by swelling measurements), indicating an interaction or bonding between the rubber and brass. Techniques previously employed with reinforcing fillers such as carbon black were used to evaluate the effect of brass on adhesion. The addition of brass powder decreased the scorch time and optimum cure time indicating that the rubber immediately surrounding the brass was being cured at a faster rate. Copper powder, on the other hand, inhibited the cure completely. When exposed to air or oxygen, even small amounts of brass catalyzed oxidation of the rubber.