Soda lignin was converted into sulfonated lignin by oxidation, hydroxymethylation, and sulfonation assisted by microwave irradiation. Oxidation and hydroxymethylation under these circumstances led to lignins with much higher reactivity toward subsequent sulfonation, and the sulfonation degree could be elevated up to 2.75 mmol g-1. A suitable microwave irradiation time is beneficial to obtain oxidized lignin with small molecular size, but the irradiation time must be selected adequately. Under optimal conditions, the sulfonated lignin exhibits a good dispersive effect to TiO2 suspension. Compared to conventional water bath heating, microwave irradiation not only increases the sulfonation degree of lignin, but also sharply shortens the reaction time.
©2011 by Walter de Gruyter Berlin Boston