Lignin‐g‐poly(acrylamide)‐g‐poly(diallyldimethyl‐ ammonium chloride): Synthesis, Characterization and Applications

The search for a renewable substitute to petroleum‐based products has fueled increasing research on lignin, an under‐utilized product from pulping processes. In this work, lignin was copolymerized with acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) under acidic conditions with Na(2)S(2)O(8) as an initiator, generating a cationic water‐soluble lignin‐g‐P(AM)‐g‐P(DADMAC) copolymer. The optimal reaction conditions, using a 5×4 factorial design experiment, were determined to be an AM/DADMAC/lignin molar ratio of 5.5:2.4:1, 90 °C, 0.26 mol L(−1) of lignin, and pH 2. Under the optimal reaction conditions, the resulting lignin‐g‐P(AM)‐g‐P(DADMAC) copolymer was 83 % soluble in an aqueous solution (at 10 g L(−1)) and at neutral pH. The copolymer had a charge density of 1.27 meq g(−1), molecular weight of (1.33±0.08) ×10(6), an AM grafting ratio of 112 wt %, and a DADMAC grafting ratio of 20 wt %. In addition, the activation energy for producing this copolymer as well as the thermal and rheological properties of the copolymer were determined. The flocculation performance of lignin‐g‐P(AM)‐g‐P(DADMAC) copolymer was evaluated in a kaolin suspension, which showed that the lignin copolymer had a comparable flocculation efficiency with the synthetic analogue of P(AM)‐g‐P(DADMAC) at pH 6.