Stabilization of Wood Color: Is Acetylation Blocking Effective?
Keywords:Acetylation, weathering, color, discoloration, ESR, reflectance, radical, yellow pine, lignin
AbstractThe color of acetylated wood was assessed by studying its response to ultraviolet light during a 56-day exposure. Change in color and reduction of reflectance signaled an interaction of acetylated wood with electromagnetic energy. Acetylated wood exhibited a color stabilization effect better than did unacetylated wood after the initial 28 days of irradiation. Its stabilization effect thereafter steadily diminished and discoloration started. Electron spin resonance (ESR) studies of photoirradiated acetylated wood and milled wood lignin divulged the generation of an active methyl radical and stable phenoxy radicals during irradiation, contributing to a quartet and a singlet signal. These free radicals originated from deacetylation and demethoxylation reactions to lignin. Moreover, ESR studies of the acetylated model compound, (4'-methyl-2'-methoxy phenoxy)-β-hydroxypropiovanillone, also divulged the cleavage of the β-0-4 linkage in lignin. It is concluded that these photo-induced degradative reactions led to the formation of phenoxy radicals which were the principal intermediates leading to the subsequent chromophoric group formations in acetylated wood.
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