Cationic tall oil lignin-starch copolymer as a flocculant for clay suspensions

In this study, a novel cationic tall oil lignin (TOL)-starch copolymer was successfully prepared by the polymerization reaction of TOL, starch and a cationic monomer of (3-acrylamidopropyl) trimethyl ammonium chloride (APTAC) through the free radical chain extension. 1H NMR and 1H–1H COSY studies demonstrated that the TOL and starch were covalently linked by the APTAC to produce the cationic copolymers. The copolymerization reaction reduced the phenolic content of TOL, yielding an increment in the solubility, molecular weight (Mw), and charge density of the cationic copolymer. Moreover, the thermochemical analysis indicated that the obtained copolymer, CR5-pH11, with the largest Mw possessed the highest glass transition temperature (Tg) of 184 °C due to the insertion of a long APTAC chain and the presence of starch and TOL. Owing to its highest charge density (3.6 meq/g) and largest Mw (56,100 kg/mol), CR5-pH11 exhibited the most efficient flocculation behavior in the kaolin suspension under altered agitation and gravitational forces as confirmed by focused beam reflectance measurement and sedimentation techniques. This study provided a new strategy to developing sustainable cationic lignin-starch flocculant for clay suspension systems.