Characteristics of Free Radicals in Wood
Keywords:Free radicals, electron spin resonance (ESR), fluorescent light, terrestrial sunlight, ultraviolet light, discoloration, loblolly pine, oxygen
AbstractFormation and behavior of free radicals in wood exposed to fluorescent light, terrestrial sunlight, and artificial ultraviolet light have been studied by electron spin resonance (ESR) spectroscopy. Freshly cut loblolly pine specimens (with 69% MC) did not exhibit any detectable ESR signals, strongly implying that intrinsic free radicals may not exist in green wood. Free radicals were readily produced by interaction of wood with electromagnetic radiations. At ambient temperature, for green wood specimens, a large amount of short-lived free radicals was generated by sunlight, whereas a relatively low amount of longer lifetime free radicals was generated by fluorescent light. For air-dried specimens, all light sources used were able to generate free radicals either in air (oxygen) or under vacuum. A large quantity of free radical concentration was normally generated under vacuum but free radicals decayed rapidly at ambient temperature. The interaction of free radicals with oxygen and the decomposition and termination of free radicals leading to the discoloration reaction were considered.
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