Study of the New Type Solvent of Cellulose

In recent decades, the development and utilization of natural polymer have been attracted increasingly because of the consumption and over-exploitation of non-renewable resources. Cellulose which consists of â-(1-4)-linked glucose repeating units is the largest renewable biological resources, it has been widely used in industrial domains such as fiber, paper, polymer, textile and food industries. However, natural cellulose is high crystalloid, strong inter- and intra-molecular hydrogen bonding caused by the hydroxyl groups and insoluble in water and common organic solvents, these properties affect their development and utilization. Therefore, the research and development of new fiber with green solvent systems, in particular, which the homogeneous reaction of cellulose derivative can occur in cellulose solvents, become a hotspot. To circumvent the use of metals in ionic fluids a variety of closed shell anions have been synthesized and these have been the main focus of ionic liquids research over the past decade. Most studies have centered on imidazolium based cations with a range of anions including BF4-, PF6-, and (CF3SO2)2N-. While these solvents show excellent solubility for a wide range of solutes and unusual miscibility with molecular liquids their widespread application will be limited by toxicological, economic and purity issues. Since none of these ionic liquids have yet been registered their general use as solvents may be restricted. Recently, we design and prepare some solvent composed of hydrogen bond, such as ionic liquid, deep eutectic solvent (DES), in which insoluble material can be dissolve. some eutectic mixtures of caprolactam, acetamide and urea were prepared. The melting point of the eutectic mixture is depressed. For example, the melting point of caprolactam/acetamide mixture in 1:1 mole ratio is 18°C, which is considerably lower than that of either of the compounds (mp caprolactam = 68~70 °C and acetamide = 78~81 °C). The significant depression of the melting point arises from an interaction between two organic molecules by hydrogen bonding. This type DES allows the mixture to be used as an ambient temperature solvent, but the solubility of cellulose in prepared DES is small. In this contribution, a new type solvent of glycerin / H2SO4 for the dissolution of cellulose is studied specially. The solubility of cellulose increases with the mole increase of H2SO4, but cellulose is carbonized when the mole ratio is over 1:2. The solubility can be up to 15% at the mole ratio 1:2. Cellulose is insoluble in the solvent adding water, thus the solvent can be renewable by distilling the water. The dissolution mechanism of cellulose in this solvent involves oxygen of H2SO4 interact with hydrogen of glycerin in the formation of oxygen anion of glycerin. After that, the hydrogen atoms of cellulose-OH act as an electron acceptor which interacts with the oxygen anion of glycerin. Upon interaction of the cellulose-OH and glycerin oxygen anion, the oxygen and hydrogen atoms from hydroxyl groups are separated, resulting in opening of the hydrogen bonds between molecular chains of the cellulose and, finally, the cellulose dissolves. Compared to ordinary ionic liquid solvents, this solvent is cheaper to prepare easily, much less toxic and non-purified. In addition, it is environmentally friendly solvent and can be recycled. Cellulose dissolution can be realized at room temperature and atmospheric pressure.