EFFECT OF SULFENAMIDE ACCELERATORS, CHEMICAL BLOWING AGENT AND GRAPHENE ON FORMATION AND PROPERTIES OF NATURAL RUBBER FOAM

Abstract

Natural rubber foam (NRF) was produced by chemical blowing technique with compression molding process. This process still has a problem with oversized dimension after removing specimen from the mold. The effect of azodicarbonamide which is the chemical blowing agent, sulfenamide accelerators and surface treated graphene with cyclohexyl diamine via diazonium reaction were investigated to solve this problem and improve properties of NRF specimen. Although the presence of azodicarbonamide can accelerate sulfur vulcanization due to amine derivatives from thermal decomposition of chemical blowing agent, NRF with high content of azodicarbonamide reduces the m order of autocatalytic reaction which means low crosslink of rubber molecules. Moreover, NRF at 4 phr of azodicarbonamide shows the smallest bubble diameter with good properties. The different chemical structures of sulfenamide accelerators are also studied. NRF with N-cyclohexyl benzothiazole-2-sulfenamide (CBS) system reveals the fastest sulfur vulcanization rate resulting in the smallest bubble diameter with narrow size distribution and lowest thermal expansion coefficient. This system also has the lowest activation energy (Ea) among other rubber foams with sulfenamide accelerators owing to high basicity from high stability of amine species after this accelerator forms as a complex species with other ingredients in sulfur vulcanization system. The last factor that should be concerned is the presence of graphene and surface treated graphene with cyclohexyl diamine via diazonium reaction. The higher graphene content in rubber matix, the faster sulfur vulcanization rate is obtained as a result of the remaining oxygen functional group on surface of graphene. Furthermore, surface treatment of graphene improved dispersion in rubber matrix. It also shows the slowest sulfur vulcanization rate due to the reaction between cyclohexyl diamine and oxygen functional groups on the graphene surface. NRF with 3 phr of treated graphene has the highest tensile strength at break due to good dispersion of graphene particle and low cell density in natural rubber foam product.