Lignin cationization with glycidyltrimethylammonium chloride aiming at water purification applications

Abstract Hardwood organosolv lignin (OSL) and enzymatic hydrolysis lignin (EHL) from softwood were cationized by glycidyltrimethylammonium chloride (GTAC) as new lignin starting materials for the reaction. The products were in detail characterized by 31 P-NMR to elucidate the reactivity of different lignin functionalities in cationization with GTAC. For OSL, a high cationization level (degree of substitution 0.74) was reached leading to a water-soluble product. For EHL, low solubility and lower reactivity were observed, likely due to the high saccharide content. Further, lower reactivity of the guaiacyl type lignin present in softwood, compared to syringyl type lignin in hardwoods, which was shown to react efficiently during the derivatization of OSL, probably played a role. In parallel to cationization, an increase of carboxylic acids (from 0.03 up to 0.55 mmol/g) in the lignin was observed as an unexpected side reaction, possibly as a result of alkaline oxygen oxidation. The applicability of the cationized lignins was tested for water purification applications in three model systems which have only sparingly been studied with cationized lignins. GTAC-OSL and GTAC-EHL were found promising for sulfate removal, with sulfate sorption capacities of up to 54 mg/g. GTAC-OSL was also found suitable for promoting kaolin settling and to some extent for humic acid coagulation.