EFFECTS OF ULTRAVIOLET ABSORBERS ON RATES OF ANAEROBIC COLORATION OF LIGNIN MODEL COMPOUNDS

The long-wave (lambda greater than or equal to 295 nm) anaerobic photo chemistry of two frequently used lignin model compounds, i.e., I lpha- (2-methoxyphenoxy)-beta-hydroxypropiophenone) and II ( ethoxyphenol)-2 -(2-methoxyphenoxy)propan-1,3-diol) was studied in the presence of thr ee UV absorbers (Tinuvin P, Tinuvin 213 and 2,4-dihydroxybenzophenone) , the additives being incorporated into thin films of I and II. Reacti ons were followed by rates of formation of new, long-wave chromophores (coloration). All of the additives reduced not only the rates of incr eased absorption, but also the extent of coloration. The most effectiv e additive was Tinuvin P. The relationship between rates of inhibited reactions and concentration of additive was nonlinear, but best repres ented by the Perrin equation, suggesting that these compounds are not acting simply as UV absorbers, but also as quenchers of excited states of I and II. (C) 1998 Elsevier Science S.A. All rights reserved.