Cationization of Eucalyptus Kraft LignoBoost Lignin: Preparation, Properties, and Potential Applications


Current changes toward a more biobased economy have recently created tremendous renewed interest in using lignin as a valuable source for chemicals and materials. Here, we present a facile cationization approach aiming to impart kraft lignin water-solubility, with similar good features as lignosulfonates. Eucalyptus globulus kraft lignin obtained from a paper mill black liquor by applying the LignoBoost process was used as the substrate. Its reaction with 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTAC) in an aqueous alkaline medium was studied to assess the impact of different reaction conditions (temperature, time, educt concentration, molar CHPTAC-to-lignin ratio) on the degree of cationization. It has been shown that at pH 13, 10 wt % lignin content, 70 degrees C, and 3 h reaction time, a CHPTAC-to-lignin minimum molar ratio of 1.3 is required to obtain fully water-soluble products. Elemental analysis (4.2% N), size-exclusion chromatography (M-w 2180 Da), and quantitative C-13 NMR spectroscopy of the product obtained at this limit reactant concentration suggest introduction of 1.2 quaternary ammonium groups per C9 unit and substitution of 75% of the initially available phenolic OH groups. The possible contribution of benzylic hydroxyls to the introduction of quaternary ammonium moieties through a quinone methide mechanism has been proposed. Since both molecular characteristics and degree of substitution, and hence solubility or count of surface charge, of colloidal particles can be adjusted within a wide range, cationic kraft lignins are promising materials for a wide range of applications, as exemplarily demonstrated for flocculation of anionic dyes.



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Pinto, PIF; Magina, S; Budjav, E; Pinto, PCR; Liebner, F; Evtuguin, D

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This work was carried out under the Project Inpactus. innovative products and technologies from eucalyptus, Project no. 21874, funded by Portugal 2020 through the European Regional Development Fund (ERDF) in the frame of COMPETE 2020 no. 246/AXIS II/2017 and within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50 011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. S.M. acknowledges FCT for the Ph.D. grant SFRH/BD/121275/2016. The authors would like to acknowledge Dr. Gonzalo Otero (University of Aveiro, Portugal) for the XPS analysis and Dr. Markus Bacher (University of Natural Resources and Life Sciences, Vienna, Austria) for recording the 1H NMR spectra.

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