Influence of the molecular weight of cellulose on the solubility in ionic liquid-water mixtures

摘要

Ionic liquids (ILs) are a novel class of solvents which have been in the focus of interest during the last few years due to their desirable properties such as high thermal stability or low vapor pressures. Some of them have the ability to dissolve cellulose without any derivatization. Different mechanisms are presented in the literatures for the dissolution of cellulose in ILs. However, the effect of the molecular weight of cellulose on the solubility in ionic liquid-water mixtures hasn´t been studied yet.The IONCELL-P is a process, which can quantitatively separate pulps into pure cellulose and hemicellulose fractions using IL-water mixtures. In this work we aim to explain the mechanism of the IONCELL-P fractionation. Ozone treatment was used to degrade cotton linter (CL) to a lower molecular weight range which is the same molecular weight range as the hemicelluloses and low molar mass cellulose in commercial pulps. The ozone treated CLs were treated with the IONCELL-P process using 1-ethyl-3-methylimidazolium acetate ([emim]OAc) and water mixtures. Different IL-Water ratios with water content between 13.5 and 19 wt% in the mixture were tested. The MMD of dissolved and undissolved cellulose were evaluated. According to these results, the effect of the molecular weight of cellulose in IL-water mixture is determining and the hypothesis of cellulose dissolution in ILs being based on the size of the polymers is supported.To validate this effect, the thesis also compares the results of the experimental data with that reported earlier by Carmen et al [30] for IONCELL-P fractionation in [emim] OAc-water using birch pulp, which contains numerous biopolymers of various chemical structures, such as cellulose and hemicellulose.