Preparation of cationic softwood kraft lignin and its application in dye removal

• Kraft lignin was cationized with glycidyl-trimethylammonium chloride.
• Reaction was optimized based on charge density and solubility of the product.
• Cationic lignin was analyzed by FTIR, TGA, NMR, GPC and elemental analyzer.
• Cationic lignin was used as a flocculant for dye removal from model wastewater.

The cationization of polymers was regarded as an effective method to improve their performance for various applications. In this work, the cationization of kraft lignin was investigated using glycidyl-trimethylammonium chloride (GTMAC) with kraft lignin in an aqueous solution under altered conditions. The conditions investigated were temperature, time, pH, GTMAC to lignin molar ratio, and lignin concentration. The optimized conditions based on charge density and solubility of cationic lignin were found to be 70 °C, 1 h, 12.5 pH, 2/1 GTMAC/lignin molar ratio, and 1.0 wt.% lignin concentration. The solubility of the resulting cationic lignin reached 90% in 1 wt.% lignin concentration and the charge density reached 1.10 meq/g under the optimized conditions. The cationic lignin was characterized and compared with unmodified kraft lignin using elemental analysis, Fourier Transform Infrared (FTIR) spectrophotometer, proton nuclear magnetic resonance (1H NMR) and thermogravimetry (TGA) analysis in order to confirm the success of the grafting reaction. The cationic lignin was used as a flocculant for dye removal (Remazol Brilliant Violet, Reactive Black, and Direct Yellow) from model wastewater.

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