One-pot preparation of zwitterion-type lignin polymers

In this work, a simple approach was examined to prepare zwitterion-type lignin (ZL) in a one-pot reaction system. Kraft lignin (KL) was modified with 3-chloro-2-hydroxypropansulfonic acid sodium salt (CHPSS) and glycidyltrimethylammonium chloride (GTMAC) in an aqueous solution simultaneously. The maximum amounts of sulfonate (1.57 mmol/g) and quaternary-N (2.16 mmol/g) groups on ZL were achieved under the reaction conditions of 7/1 molar ratio of CHPSS/KL, 9/1 molar ratio of GTMAC/KL, 40 g/L concentration of KL, 3/5 molar ratio of NaOH/KL, 4 h reaction time and 80 °C. The chemical structure, thermal stability, and surface activity of the ZL were compared with those of cationic lignin (CL) and sulfonated lignin (SL) produced under optimized conditions. The signals for hydrogen, carbon, and hydrogen‑carbon in the spectra of ¹H-, ¹³C-, and HSQC-NMR indicated that the sulfonation and quaternization occurred on both aliphatic and phenolic hydroxy groups of lignin. The flocculation performance of ZL for simulated dye wastewater was further analyzed. The main novelties of this work were the introduction of a one-pot process to simultaneously impart anionic and cationic functional groups onto kraft lignin, and the development of a new biodegradable zwitterion-type flocculant for removing dye pigments from a simulated solution.