30. Cai, Wensheng; Anderson, Eric C.;
Gupta, Ram B. Separation of lignin from
aqueous mixtures by ionic and nonionic temperature-sensitive hydrogels.
Three ionic and nonionic temp.-sensitive hydrogels, poly(N-isopropylacrylamide) (I), poly(N-isopropylacrylamide-co-acrylic acid), and poly(N-isopropylacrylamide-co-hydroxypropyl methacrylate), were synthesized and used to conc. the lignin (II) solns. of interest in the pulp and paper industry. The interactions between hydrogels and solutes played an important role in the sepn. Because of the absorption of II in the hydrogels, the sepn. efficiency of the I hydrogel is low. By introducing the hydrophilic monomers acrylic acid and hydroxypropyl methacrylate into the I hydrogel, the sepn. efficiencies were increased because of the ionic repulsion between II and the incorporated hydrophilic groups. In addn., the sepn. efficiencies were affected by the extent of crosslinking and the solute concn. The time dependence of the sepn. efficiency suggests that the sepn. is diffusion-controlled.