Free radical reactions weathered wood

Sunlight, especially a small portion of UV light, is the principal instigator of weathering reactions. The immediate consequence of the interaction of wood with light is the generation of free radicals at the exposed surface (7, 19). As these labile free radicals terminate and stabilize, chromophoric and auxochromic groups are formed and discoloration and deterioration occur. 

Free Radical Characteristics and Reactions in Weathered Wood. Wood, wood fiber components, and isolated lignin contain certain amounts of free radicals that are detectable by ESR spectroscopy (SS, S9). Unexposed green wood with 69% moisture content (in dark and in vacuo) was found (77a) to contain no free radicals. A trace amount of free radicals may be produced in the presence of oxygen, and most of these free radicals are generated in wood during mechanical preparation (90) as well as in wood exposed to electromagnetic irradiation. ESR studies revealed that wood interacts readily... 

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