Two-Step Modification Pathway for Inducing Lignin-Derived Dispersants and Flocculants

Kraft lignin is an underutilized material mainly combusted in the pulping industry. Its conversion to value-added products for further end-use applications is limited due to its insolubility in water. In this work, the modification of kraft lignin (KL) was conducted through oxidation and carboxymethylation to generate anionic water-soluble lignin (OKL, and CMKL, respectively). The results indicated that these biopolymers acted as effective dispersants in an aluminum oxide suspension. Subsequently, generated biomaterials were polymerized with acrylamide monomer to generate flocculants (i.e., OKL-AM and CMKL-AM) for the aluminum oxide suspension. The properties of polymers were characterized extensively, and the polymerization of OKL and CMKL with acrylamide increased the molecular weight (M w ) of the biomaterials from 16 × 10 3 and 28 × 10 3 to 684 × 10 3 and 387 × 10 3 g/mol, respectively. Flocculation studies under stirring revealed that the chord length of aluminum oxide particles increased substantially by treating the suspension with the OKL-AM polymer. The reflocculation analysis provided further insight into the reversibility and high strength of formed flocs. Our results confirmed that by following a one-step reaction, a lignin-based dispersant could be generated, and further polymerizing the biomaterials (i.e., dispersants) would make it a valuable flocculant. This investigation confirms a versatile and environmentally friendly pathway to convert a waste material (i.e., lignin) to a green dispersant and flocculant. Graphic Abstract