The free radical species in polyacrylonitrile fibers induced by γ-radiation and their decay behaviors

Free radicals in vacuum, air and oxygen atmospheres were studied using electron spin resonance (ESR). Mainly two types of radicals, namely alkyl radicals and polyimine radicals, are formed in polyacrylonitrile (PAN) fibers after γ-ray irradiation. The G value of the radical formation was calculated to be 2.1 (number of radicals per 100 eV absorbed) in air at room temperature based on the ESR measurements. The radical stability and decay behaviors at room temperature and elevated temperatures were also investigated under different atmospheres. The alkyl radicals were found to be rather stable when stored in vacuum at room temperature, but they decayed via reaction with oxygen when stored in air. The alkyl radicals disappeared completely after a thermal treatment at 110 °C in vacuum, but only 15% of the polyimine radicals decayed; this indicates that polyimine radicals are more stable compared to the alkyl radicals due to their lower mobility.

► Radicals formed by radiation were assigned to polyimine and alkyl radicals.
► G-value of radicals was measured to be 2.1 per 100 eV.
► The radicals were found to be extremely stable in vacuum at room temperature.
► Effect of oxygen on radical decay under various conditions was studied.