Relation of Peroxide Decomposition to Rubber Degradation

Abstract

It appeared that an investigation of the reactions between peroxides and deactivators of rubber degradation, such as mercaptobenzimidazole, would help to explain the action of these sulfur compounds. Le Bras, who proposed the use of these compounds, considered that they function by deactivating the peroxides formed by autoxidation. It was found that mercaptobenzimidazole and simpler related compounds such as thiourea reacted with alkyl hydroperoxides with the formation of hydroxyl or alkoxy radicals and this led to attack on the solvent or on other molecules present, in a manner resembling the action of ferrous salt-hydrogen peroxide. This suggested that rubber would also be attacked and probably degraded. It was found that mercaptobenzimidazole with excess of peroxide gave rapid degradation of rubber in solution if access of oxygen was permitted. Thiourea, thioacetamide, some dithiocarbonates, and aromatic thiols were also effective, but aliphatic thiols and ethylmercaptobenzimidazole were ineffective. Softened or “depolymerized” rubber was prepared by addition of the reagents to rubber solutions or to latex. The use of these sulfur compounds in the presence of peroxides provides a means of obtaining a controlled amount of breakdown of rubber, and products ranging from normal plasticized rubber to a viscous liquid can be prepared. Under different conditions, mercaptobenzimidazole may either promote degradation (as shown in this paper) or retard it (as stated by Le Bras), and a possible explanation for this reversal of behavior is suggested.

GTR/NBR/Silica Composites Performance Properties as a Function of Curing System: Sulfur versus Peroxides

“…Furthermore, it should also be pointed out that the components also present in GTR (e.g., carbon black, curing agents’ residue, etc.) might have an impact on the efficiency sulfur curing system [ 45 , 46 ] and peroxides [ 47 , 48 ] during the formulation of materials modified with GTR.…”