Influence of rubber composition on change of crosslink density of rubber vulcanizates with EV cure system by thermal aging

Variation of the crosslink density of a rubber vulcanizate depending on the rubber composition after the thermal aging was studied with single rubber, biblend, and triblend vulcanizates of natural rubber (NR), butadiene rubbe r (BR), and styrene-butadiene rubber (SBR). The efficient vulcanization (EV ) system was employed to minimize the influence of free sulfur in the vulca nizate on the change of the crosslink density. Thermal aging was performed at 40, 60, and 80 degrees C for 20 days with 5-day intervals. The crosslink densities of the vulcanizates after the thermal aging increase. For the si ngle rubber vulcanizates, variation of the crosslink density by the thermal aging has the order: SBR > BR > NR. For the biblend vulcanizates, variatio ns of the crosslink densities of the NR/SBR and SBR/BR blends are larger th an that of NR/BR blend. Variation of the crosslink density of the vulcaniza te increases by increasing the SBR content in the vulcanizate. Variation of the crosslink density of the rubber vulcanizate depending on the rubber co mposition was explained by miscibility of the blends, combination reaction of the pendent groups, and mobility of the pendent group. (C) 2000 John Wil ey & Sons, Inc.