Effect of Urea/choline chloride treatment on removing hemicellulose during alkali extraction in the preparation of high-purity dissolving pulps

Urea/choline chloride (ChCl) treatment is effective in removing hemicellulose during the production of high-purity dissolving pulps. In this study, the mechanism of hemicellulose removal was explored by analyzing the changes in hydrogen bonding in holocellulose and hemicellulose before and after urea/ChCl treatment. The results demonstrated that the urea/ChCl system enhanced the pentose removal efficiency to 24.60 % during the alkali extraction stage. The crystallinity index and crystalline size of hemicellulose decreased, whereas those of holocellulose increased. Nuclear magnetic resonance (NMR) and Fourier transform–infrared (FTIR) spectroscopy peak-fitting results demonstrated that the intermolecular hydrogen bond at 3200–3300 cm−1 in holocellulose decreased after the treatment, the hydrogen bonds of hemicellulose are disrupted and the proportion of hydrogen-bond hydroxyl groups decreased, indicating that adding urea/ChCl could break the hydrogen bonding connection between hemicellulose and cellulose. This work provided a theoretical basis for identifying the connection mechanism between cellulose and hemicellulose. [Display omitted] •Selective Removal of pentose from high purity dissolving pulp.•The influence of urea/choline chloride on the crystallinity index.•FTIR peak-fitting results showed three types of hydrogen bonds.•The proportion of hydroxyl groups involved in the formation of hydrogen bonds in hemicellulose was investigated.