Preparation of octopus-like lignin-grafted cationic polyacrylamide flocculant and its application for water flocculation.

High efficiency lignin-grafted cationic polyacrylamide (L-CPA) flocculant was synthesized via "grafting to" method using acrylamide (AM), methylacryloyloxyethyltrimethyl ammonium chloride (DMC) and enzymatic hydrolysis lignin (EHL) as raw materials. The linear pre-polymer of cationic polyacrylamide (CPA) terminated with chlorine was first synthesized and then grafted onto EHL via reactions of chlorine with phenolic hydroxyl groups in lignin molecules. The synthesized L-CPA could self-assemble into octopus-like nanospheres with CPA segments dissolved in water and hydrophobic lignin skeletons concentrated in the core, which endowed the L-CPA with excellent flocculation efficiency for kaolin suspension under faintly acid, neutral or alkalescent conditions (pH = 5-9). Only a small dosage between 4.0-4.5 mg/L of L-CPA was needed for flocculation of the kaolin suspension. The charge neutralization and bridging effect was proposed for the flocculation mechanism of the lignin-grafted cationic polyacrylamide. The octopus-like L-CPA was cheap, environmentally friendly and technically feasible, showing a great prospect in wastewater treatment.