Synthesis and characterization of lignin‐based cationic dye‐flocculant

Kraft lignin derivatives having cationic poly 2‐(trimethylamino)ethyl methacrylate side chains were synthesized and their property as dye‐flocculant was investigated. Lignin‐based flocculants having three types of side chain densities and three types of side chain lengths were synthesized by esterification of the lignin hydroxyl groups with bromoisobutyryl groups, atom transfer radical polymerization using 2‐(dimethylamino)ethyl methacrylate, and quaternization of the amino groups. Dye removal test was performed using three organic dyes and the obtained lignin‐based flocculants. The results indicated that the density and the length of the side chains obviously affected the flocculation behavior. When the flocculants containing the same nitrogen amount were compared, the flocculation performance was improved with the increase of the side chain length within the samples having low and middle side chain densities. In the case of the samples having high side chain density, the most efficient sample was not the sample having the longest side chain. Most of the lignin‐based flocculants removed dyes more efficiently than the poly 2‐(trimethylamino)ethyl methacrylate homopolymer. From these results, it was suggested that lignin has a potential character as the core molecule to design the high‐efficient dye‐flocculant. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46611.