Solubility and Dye-Binding Properties of Quaternized and Peroxidase-Polymerized Kraft Lignin

Abstract

The ability of cationic Kraft lignin to function as a flocculant for decolorization of textile wastewaters was examined. Kraft lignin was quaternized with high efficiency in alkaline solution with 3-chloro-2-hydroxypropyl-trimethylamonium chloride. The product formed was separated into two fractions arbitrarily based on their aqueous solubility at pH 7. The pH 7-soluble fraction was soluble over the pH 2 to 13 range. The pH 7-insoluble fraction was soluble at low (< pH 4) and high pH (> pH 12). Treatment of the pH 7-soluble quaternized lignin fraction with soybean peroxidase and hydrogen peroxide under nitrogen produced a soluble, high molecular weight polymer, as determined by ultrafiltration analysis. Peroxidase treatment of the pH 7-insoluble fraction at pH 3 produced a material not completely soluble at any pH, probably by modifying the lignin structure but not necessarily by increasing its molecular weight. All quaternized lignin fractions were demonstrated to bind Orange II and hydrolyzed Reactive Red 180, but only peroxidase-polymerized lignin produced rapidly settling flocs. Peroxidase-treated, quaternized Kraft lignin can be used in place of synthetic cationic polymers for decolorization of textile wastewaters.