Research progress on mechanism of cellulose dissolution
XU Feng;CHEN Yanglei;YOU Tingting;MAO Jianzhen;ZHANG Xun;Beijing Forestry University,Beijing Key Laboratory of Forestry Biomass Chemistry;Qilu University of Technology,Key Laboratory of Pulp and Paper Science & Technology Ministry of Education;
As one of the main components in plant cell wall,cellulose is a homogeneous glycan formed by glucose through 1,4-β glycosidic bond,which can be used to produce chemical products such as cellulose-based esters and ethers. The preparation and application of these cellulose-based products are closely related to their dissolution aspects.Exploring the dissolution mechanism of cellulose is crucial to find out efficient and green solvents for the cellulose dissolution. This paper reviewed the current explanations of cellulose dissolution mechanisms and factors that may affect dissolution,such as cellulose crystallinity,temperature,and kinetic factors. Recent work has also emphasized on the role of cellulose charge and the concomitant ion entropy effects,as well as hydrophobic interactions. Generally,scholars believe that the mechanism of cellulose dissolution is based on the theory of hydrogen bond destruction. There are a large number of hydrogen bonds between and within cellulose molecules and breaking the hydrogen bonds in cellulose may cause cellulose dissolution. Despite the reasonable assumption of hydrogen bond destruction theory,there are still some unclear problems,such as the reason why cellulose is insoluble in water cannot be explained. It is suggested that,other than hydrogen bond,the Van der Waals' force and hydrophobicity existed in the complex systems should be considered. The debating points related to the mechanisms of cellulose dissolved in ionic liquid were also reviewed.The theory of kinetic control indicates rather than thermodynamic control is decisive but still lack of adequate supporting data. There are many statements emphasizing the crucial role of the IL anion especially chloride ions except that of cations. Moreover,further research about other ions is needed to fully understand the dissolution mechanism. Some researchers indicated that the cationic amphiphilicity of ionic liquid was the key for dissolution. They found that almost all cations that promoted dissolution were amphiphilic. Furthermore,it is generally acknowledged that only nitrogencontaining cations work,and all the cations used that work are amphiphilic. From the previously mentioned attempt to reviewthe literature on cellulose dissolution,it can be inferred that the amphiphilic property may be the key theory for cellulose dissolution. We therefore put forward a hypothesis that we should focus on looking for novel amphiphilic solvents in the future.It is hoped that this treatise contributes to a deeper understanding of cellulose dissolution,and in particularly,the amphiphilic theory,to help find high-efficient,environmental-friendly and low-cost solvents for cellulose dissolution.
【CateGory Index】： O636.11
【CateGory Index】： O636.11