Zhang Jinming

Transparent and flame retardant cellulose/aluminum hydroxide nanocomposite aerogels

Cellulose-based nanocomposite aerogels were prepared by incorporation of aluminum hydroxide (AH) nanoparticles into cellulose gels via in-situ sol-gel synthesis and following supercritical CO2 drying. The structure and properties of cellulose/AH nanocomposite aerogels were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, ultraviolet-visible spectrometry, N2 adsorption, thermogravimetric analysis, and micro-scale combustion calorimetry. The results indicated that the AH nanoparticles were homogeneously distributed within matrix, and the presence of AH nanoparticles did not affect the homogeneous nanoporous structure and morphology of regenerated cellulose aerogels prepared from 1-allyl-3-methylimidazolium chloride solution. The resultant nanocomposite aerogels exhibited good transparency and excellent mechanical properties. Moreover, the incorporation of AH was found to significantly decrease the flammability of cellulose aerogels. Therefore, this work provides a facile method to prepare transparent and flame retardant cellulose-based nanocomposite aerogels, which may have great potential in the application of building materials.

Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose

The effect of ionic liquids (ILs) on the solubility of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through nuclear magnetic resonance (NMR) spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissolution. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions associated with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.

Homogeneous synthesis of cellulose derivatives in ionic liquids

Cellulose derivatives are important fine chemicals with a wide range of applications in modern industries, so that cellulose derivatization has been one of hot topics for a long time. However, the existence of numerous hydroxyls in cellulose also generates a well-developed intra- and inter-molecular hydrogen bonding network, thus natural cellulose is neither meltable nor soluble in conventional solvents. Until today, the preparation method for cellulose esters begins with a heterogeneous reaction between cellulose and a large excess of the acylation reagent in the presence of pyridine or sulfuric acid as the catalyst. These heterogeneous reactions cause some problems, such as uneven distribution of substituents, side reactions, time consumption and considerable degradation of cellulose. Homogeneous esterification of cellulose in appropriate media, the alternative procedure for heterogeneous process, has been one focus in cellulose chemistry. It not only provides opportunities to obtain the effective control of degree of substitution (DS), distribution and uniformity of the functional groups along cellulose chains, but also creates more options to induce novel and functional groups. Recently, the advent of ionic liquids that can dissolve cellulose provides a new and versatile platform for the efficient and homogeneous derivatization of cellulose. A variety of well-known, novel and functional cellulose esters have been successfully synthesized in ionic liquids. Meanwhile, development of esterification techniques, utilization of agricultural residues, and pilot scheme of up-scaling esterification in ionic liquids have been in progress continuously. This review summarizes the development in homogeneous synthesis of cellulose esters in ionic liquids published in the recent decade.