Lignin-acrylamide-diallyl dimethylammonium chloride copolymer: mechanism of polymerization and purification

Abstract

The world economy is growing faster than ever, while environmental issues are getting worse. The use of ecologically friendly materials has increased as a result of environmental concerns. Promoting ecologically friendly products will be greatly aided by biomass, which is a renewable resource. Lignin, as a main component of lignocellulosic biomass and one of the most abundant biopolymers, is utilized extensively in a variety of industrial domains. It has

been proposed that lignin can be grafted with a variety of monomers, including glycidyl- trimethylammonium chloride (GTMAC), acrylamide (AM), and acrylic acid (AA) to produce

water soluble products.

In this study, a detailed investigation was carried out on the free-radical polymerization of kraft lignin, acrylamide (AM), and diallyl dimethylammonium chloride (DADMAC) to generate flocculants for wastewater treatment. To comprehend the physicochemical properties of this copolymerization system, in-situ nuclear magnetic resonance (NMR), rheological analysis, and particle size techniques were conducted. The copolymerization of lignin-AM and lignin-DADMAC had an activation energy of 65.7 and 69.3 kJ/mol, respectively, and followed the first-order kinetic model, which was monitored by in-situ 1H NMR results. The highest conversions of AM and DADMAC were 96% and 68%, respectively, in the copolymerization of lignin, AM, and DADMAC at the molar ratio of 5.5: 2.4: 1, pH 2 and 85°C. It evidenced that the participation of AM in the reaction was essential for polymerizing DADMAC to lignin due to less steric hindrance of AM than DADMAC facilitating its bridging performance. Lignin acted as an inhibitor in the copolymerization reaction, indicated by the monomer conversion ratio and dynamic rheology of the reaction system. [...]