Oxidative stress relaxation of blends of cis‐1,4‐polybutadiene and natural rubber

Abstract

AbstractBlends of cis‐1,4‐polybutadiene and natural rubber were vulcanized with dicumyl peroxide and a CBS (N‐cyclohexylbenzothiazole‐2‐sulfenamide) accelerated sulfur system. For the peroxide‐cured systems, soft vulcanizates had the natural rubber component only very lightly crosslinked and showed pronounced flow at room temperature. The oxidative stress relaxation of the hard vulcanizates at 80°C. in air was intermediate between that of the pure polymers. Intermittent stress relaxation measurements on these vulcanizates showed pronounced crosslinking during the aging of the pure polybutadiene and the 50/50 blend. Soft blends prepared by the accelerated sulfur system also showed flow due to the lightly crosslinked polybutadiene component. The unextracted hard blends resembled the pure polybutadiene vulcanizate in oxidative stress relaxation behavior at 80°C. in air, whereas after extraction to remove residual antioxidant and vulcanization products, etc., the blends were similar to natural rubber at all levels.