The effect of different antioxidant compounds and their mixture on the
thermal oxidation behaviour of electron-beam-irradiated styrene-butad
iene rubber (SBR) has been investigated. The compounds used were N-(1,
3-dimethyl-butyl) N'-phenyl-p-phenylenediamine (I); 4,4'-thiobis(6-ter
t-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 ox
idation response was evaluated by measurement of the percentage retent
ion of tensile strength and ultimate elongation of the EB-irradiated S
BR samples after they had been thermally aged in air at 100 degrees C
for up to 14 days. The results indicate a remarkable antioxidant effic
iency 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 hydroge
n 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 radica
ls, produced from the interaction of polymer and hydroperoxide, and th
iyl radicals of the antioxidant.