Acid hydrolysis of kraft lignin-acrylamide polymer to improve its flocculation affinity

Abstract To explore the production of anionic lignin polymer with a high charge density as a flocculant, lignin-acrylamide (KL-AM) was generated and subsequently hydrolyzed under various conditions. The hydrolysis reaction was optimized to generate the anionic lignin polymer with high anionicity. KL-AM and hydrolyzed lignin polymer (HKL-AM) had a molecular weight of 1,564 kg/mol and 601 kg/mol and charge density of -2.33 meq/g and -3.62 meq/g, respectively. Adsorption, turbidity, mass balance, and chord length analyses confirmed the more efficient flocculation affinity of HKL-AM than KL-AM and polyAM in flocculating aluminum oxide particles in suspension systems. The results also indicated that the charge density of the lignin derivative was contributed greatly to the strength of flocs, but the molecular weight of the macromolecule significantly affected the deflocculation tendency of the particles. The results confirmed that the hydrolysis could be used as a reliable approach to improve the anionicity of lignin-acrylamide polymers and thus the flocculation affinity of the polymers at the expense of a molecular weight drop.