Influence of γ-irradiation on proton spin–lattice relaxation of SBR used as antirads and its ESR investigation

Proton spin–lattice relaxation time t₁ was measured on SBR samples with carbon black or kaolin filler using modified linseed oil. The NMR pulse technique at 90MHz was used in the temperature range from 180 to 400 K. The temperature dependence of t₁ indicates that samples filled with carbon black have similar molecular dynamics to the standard unfilled SBR samples. The activation energy for the motion of the main chain for these samples amounts to 16.4kJ/mol. Samples containing linseed oil modified with para-toluidine showed an activation energy of about 14.6kJ/mol and were not affected by γ-irradiation. Values of the minimum relaxation time t^min₁ were increased by γ-irradiation in comparison with a standard SBR sample. ESR measurements carried out at room temperature by means of an X-band spectrometer indicated that unidentified radicals within the rubber were formed during its mastication with vulcanizing additives. The ESR spectra did not change during the vulcanization process. Samples filled with carbon black showed a broadening of the ESR line; this is consistent with the increase in the electrical conductivity.