Mechanisms involved in the recycling of NR and EPDM

The thermochemical recycling of natural rubber (NR) and ethylene-propylene- diene rubber (EPDM) vulcanizates with disulfides was studied, NR sulfur vul canizates were completely plasticized when heated with diphenyldisulfide at 200 degrees C. It could be concluded that both main chain scission and cro sslink scission caused the network breakdown. NR peroxide vulcanizates were less reactive towards disulfide at 200 degrees C, and only reacted through main chain scission. For EPDM a temperature range of 200-275 degrees C was Studied. In the prese nce of diphenyldisulfide at 200 degrees C there was almost no devulcanizati on of EPDM sulfur vulcanizates, and at 225 and 250 degrees C there was only slightly more devulcanization. A decrease in crosslink density of 90% was found when 2 x 10(-4) mol diphenyldisulfide/cm(3) vulcanizate was added and the EPDM sulfur vulcanizates were heated to 275 degrees C. EPDM peroxide v ulcanizates showed a decrease in crosslink density of ca. 40% under the sam e conditions. The lower reactivity of EPDM towards disulfide compared with NR is the resu lt of higher crosslink densities, the presence of a higher percentage of mo re stable monosulfidic crosslinks and the fact that EPDM is less apt to mai n chain scission relative to NR.