ULTRASOUND DEVULCANIZATION OF SULFUR VULCANIZED SBR - CROSS-LINK DENSITY AND MOLECULAR MOBILITY

Sulfur-cured SBR vulcanizates are devulcanized by high power ultrasoni c irradiation in a continuous process under various processing conditi ons. Crosslink density and gel fraction of devulcanized rubber are mea sured. The unique dependence of crosslink density on gel fraction of d evulcanized samples obtained at various processing conditions is estab lished. DSC studies indicate a significant increase in the glass trans ition temperature of the devulcanized rubber having crosslink density lower than that of the original vulcanizates. Solid state NMR studies confirm that these changes in T-g are due to a decrease of molecular m obility as measured by a decrease in spin-spin relaxation time. Ultras onic devulcanization is accompanied by a significant increase in cis-t rans isomerization, Chemical changes explaining the observed phenomena are discussed.