Devulcanization of sulfur-cured isoprene rubber in supercritical carbon dioxide

摘要

A new devulcanization process that utilizes supercritical CO_2 along with devulcanizing reagents was studied.Unfilled isoprene rubber samples with different crosslink distributions were prepared by controlling the curatives and the cure time.The vulcanizates were subjected to the Soxhlet extraction using azeotropic acetone/chloroform to remove residual curatives.The devulcanizations were performed under various conditions of temperatures (140-200 degC) in the presence of supercritical CO_2 for 60 min.The products were fractionated into sol and gel fractions,and molecular weights of the sol fractions and crosslink densities of the gel fractions were determined.Thiol-amine reagent was found to be effective among several devulcanizing reagents;the molecular weight of the resulted sol fractions were about tens of thousands and the crosslink densities of gel fractions decreased substantially from the initial ones.Yields of sol fractions increased with the increase of the CO_2 pressure.In a supercritical fluid state of CO_2 the vulcanizates were more efficiently devulcanized to sol fractions than in an ordinary gaseous state of CO_2.The higher contents of polysulfidic crosslink in the vulcanizates have led to the larger amount of sol fractions.These results suggest that the devulcanizing reagents penetrate and diffuse into the vulcanizates in the presence of supercritical CO_2 and the preferential scission of polysulfidic crosslink sites is observed.