Radiation- and Thermal Treatment-Induced Radicals in Polyacrylonitrile Fibers Studied by ESR

Abstract

Abstract:

The free radicals in polyacrylonitrile (PAN) fibers induced by γ-ray irradiation and thermal treatment were studied using electron spin resonance (ESR) technique. The radicals produced by radiation in air and vacuum at room temperature were assigned primarily to alkyl (H abstraction from methine) and polyimine radicals. These radicals were found stable at room temperature, but decayed with increasing temperature in air until 150 ℃. A new type of radical was formed in original PAN fibers at 190 ℃ in air, and the concentration of the radical increased significantly with temperature. Much less radicals were formed if the PAN fibers were heated in vacuum. It could be speculated that the new type of radical observed was related to thermal-oxidation reactions. This type of radical was attributed to a polyenyl radical located on the conjugated structure, and the conjugation length increased with temperature.

Key words: ESR, free radical, PAN fiber, radiation, thermal-oxidation

CLC Number:

O632.6

LIU Wei-Hua, WANG Mou-Hua, WU Guo-Zhong. Radiation- and Thermal Treatment-Induced Radicals in Polyacrylonitrile Fibers Studied by ESR[J]. Chinese Journal of Magnetic Resonance, 2011, 28(4): 447-453.

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