Contribution of lignin to the reactivity of wood in chemical modifications I: Influence of delignification on acetylation

Abstract

In order to examine the contribution of wood components to the acetylation of wood, we acetylated wood meal that had been partially delignified. The results were analyzed in terms of the reaction kinetics. The first-order rate equation was successfully adjusted to the weight gain data. The rate constant for acetylation initially increased with progress of lignin elimination and then turned to decrease; the apparent activation energy showed the reverse tendency and ranged from about 90 to 130 kJ/mol. These results suggest that lignin elimination brings not only separation of lignin but also drastic change of the chemical and/or physical structure in the residual lignin, and this affects the reactivity of wood meal as a whole. The ultimate weight gain estimated by the regression of the rate equation showed a minimum when lignin was moderately eliminated, which was explained in terms of enhanced reactivity of lignin and lower accessibility for holocellulose than predicted. The equilibrium moisture content had a maximum when lignin was moderately eliminated. This tendency is the opposite of that observed for the ultimate weight gain, and suggests that the sites for acetylation do not always correspond to those for moisture adsorption. © 2007 The Japan Wood Research Society.