STABILIZATION OF RADIATION-VULCANIZED SBR AGAINST THERMAL-OXIDATION

The effect of different antioxidant compounds and their mixture on the thermal oxidation behaviour of electron-beam-irradiated styrene-butadiene rubber (SBR) has been investigated. The compounds used were N-(1,3-dimethyl-butyl) N'-phenyl-p-phenylenediamine (I); 4,4'-thiobis(6-tert-butyl-m-cresol)(II); nickel dibutyl dithiocarbamate (II); trisnonyl phenyl phosphite (IV) and 2-mercapto-benzimidazol (V), and mixtures of (I and III), (I and IV), (II and III) and (II and IV). The thermal oxidation response was evaluated by measurement of the percentage retention of tensile strength and ultimate elongation of the EB-irradiated SBR samples after they had been thermally aged in air at 100 degrees C for up to 14 days. The results indicate a remarkable antioxidant efficiency of (V) for SBR compared to either the other single antioxidants or their mixtures. The high efficiency of (V) may be attributed to its main function as a preventive peroxide decomposer. The labile hydrogen attached to the nitrogen atom may also act in chain breaking. Also, the possibility exists that at least a small degree of linking occurs during compounding and vulcanization via the saturation of the double bonds of butadiene units by antioxidants or via the macro alkyl radicals, produced from the interaction of polymer and hydroperoxide, and thiyl radicals of the antioxidant.