Synthesis and characterization of carboxymethylated alkali lignin in organic solvent medium

The effects of the volume ratio of water to ethanol, the reaction temperature and the way of NaOH addition on the conversion ratio of carboxymethylation of wheat straw alkali lignin (WAL) and the carboxyl group content of the obtained carboxymethylated alkali lignin (CML) were examined by single factor experiments. The results show that the conversion ratio of WAL is up to 94.798% of and CML with the carboxyl group content of 2.764 mmol/g can be obtained with the following conditions: reaction temperature of 70°C, the volume ration of water to ethanol of 20:80 as the reaction medium and adding NaOH twice. The FT-IR and 13C-NMR spectroscopy show that the carboxymethyl groups are successfully engrafted into the WAL molecule structure, and the carboxymethylation substitutions simultaneously occur in the phenolic hydroxyl group and the α-position aliphatic hydroxyl group of the WAL molecule.