Lignocellulosic materials such as wood pulp fibers are negatively charged by nature, but they can be covalently modified with the same reagent that is widely used for the cationization of starch. The product may then serve for example in wastewater treatment or in papermaking. We used different solvent systems to investigate their impact on the reaction efficiency of the cationization of cellulosic fibers. In this study, a bleached softwood Kraft pulp was cationized with 2,3-epoxypropyltrimethylammonium chloride. One protocol was chosen for a reaction in water; in further assays, 90% of the water was replaced by organic solvents. “Blank” reactions in which the material was treated with sodium chloride instead of the epoxide reagent were included in the study. The effects of the reaction conditions on pulp properties were tracked by infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. Because the reagent-to-sample ratio was kept constant, changes in the degree of substitution translate directly into differences in reaction efficiency. With our protocol, both the reaction in water only and the reaction in dimethyl sulfoxide yielded a degree of substitution around 0.05. Isopropanol tripled the degree of substitution; tetrahydrofuran even gave a tenfold increase in reaction efficiency. The molar mass distribution was not notably affected by treatment in water, isopropanol, and tetrahydrofuran, while the use of dimethyl sulfoxide caused a decrease. In the thermogravimetric analysis of all treated samples, cellulose degradation was fastest around 370°C. Cationized samples featured an additional degradation peak around 310°C; its magnitude was roughly correlated to the degree of substitution. The increased hydrophilicity of the cationized materials could be quantified, but was already easily seen during workup. In conclusion, cationization of pulp yields a material with reversed charge and increased hydrophilicity. Our experiments improved the understanding of the reaction system and the influencing factors. In particular, we showed that in cases where a decrease in the liquid-to-solid ratio is limited, the reaction efficiency can be improved by partially substituting water with organic solvents. From all tested systems, a tetrahydrofuran-water-mixture is the best choice for controlling the degree of substitution without changing the molar mass of the polymeric backbone or otherwise affecting cellulose integrity.

How to cationize lignocellulosics more efficiently

251st National Meeting (2016)

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