DEVULCANIZATION OF UNFILLED NATURAL RUBBER IN SUPERCRITICAL CARBON DIOXIDE

摘要

Sulfur-cured unfilled natural rubber (NR) was devulcanized in supercritical CO_2 along with diphenyl disulfide (DD) as a devulcanizing reagent. The product was fractionated into sol and gel fractions. The sol fraction increased with the increase of CO_2 pressure, especially over the critical point. The observed sol fraction was 50% by weight under the condition of 180°C, 10 MPa in 60 min. The molar mass of the resulted sol fraction was about tens of thousands and the crosslink density of gel fraction decreased from the initial one. Carbon―13 NMR study showed that cis-trans isomerization occurred during the devulcanization. Tg of the sol fraction was a little higher than that of NR. It is also suggested that the devulcanization tends to proceed more easily with the increase of polysulfidic crosslinks in the vulcanizate.