Devulcanization of carbon black filled natural rubber using supercritical carbon dioxide

Natural rubber (NR) vulcanizates filled with various contents of carbon black were devulcanized in supercritical CO2 in the presence of diphenyl disulfide as a devulcanizing reagent. The devulcanized rubbers were separated to sol and gel components using chloroform. Regardless of the carbon black content in the NR vulcanizates, sol fractions of 20–40% were obtained and the swelling ratios of the gel components were higher than the original vulcanizates. Dynamic mechanical properties of the devulcanized rubbers were also investigated. Devulcanized rubbers showed a slightly lower G′ values and slightly higher tan δ values than the initial compounds and much lower G′ values and much higher tan δ values than the vulcanizates. These results indicate that the presence of carbon black in NR vulcanizates does not disturb the devulcanization. A NR‐based truck tire vulcanizate was also devulcanized. The physical properties of recycled rubber made from virgin rubber and various contents of the devulcanized tire rubber were measured. The decrease in tensile strength was only around 10% at up to 40 phr of the devulcanized tire rubber content.