关键词: 点击化学, 纤维素, 半纤维素, 木质素

Abstract: Chemical modification can improve the compatibility of lignocellulose with polymeric matrices, and make lignocellulose owned specific function. Click chemistry, a kind of important method used for chemical modification, was firstly proposed by Sharpless and co-workers in 2001. Its typical reaction types include copper-catalyzed azide-alkyne cycloaddition (CuAAC), strain-promoted alkyne-azide cycloaddition reaction (SPAAC), thiol-ene/yne click reaction and diels-alder click reaction, etc. Compared with the traditional grafting modification method, click chemistry was found to be mild reaction conditions, environmental friendly, easy to implement and very efficient. It has been applied in the chemical modification of lignocelluloses. In terms of click reaction method, the CuAAC reaction is the most common click reaction used for the chemical modification of lignocellulose. However, the catalyst is difficult to remove after the CuAAC reaction so that the application of the products is limited to some extent. The Cu (Ⅰ), which is linked with aerogels of cellulose nanofibrils through covalent bonding, can be recycled efficiently after click reaction. Compared with the CuAAC reaction, the Thiol-Ene/Yne reaction does not need the toxic copper as a catalyst. In terms of cellulose research, hydrogel and nanoplatelet could be prepared with cellulose itself or both cellulose and polymer by click reactions. In addition, click reaction could be proved by fluorescence labeling for cellulose, and cellulose nanofibrils with multi-color fluorescent labelling could be prepared through two click reaction. In terms of hemicellulose and lignin research, the copolymer of xylan and polylactic acid was formed by click reaction. The glass transition temperature of the copolymer was lower than that of xylan, and the thermal decomposition temperature of the copolymer was higher than that of xylan. The triazole-linked xylosides and xylobiosides could be achieved through CuAAC reaction. A thermoplastic polymer could be prepared with lignin and polystyrene by click reaction. In addition, bioorthogonal click chemistry could be commissioned to visualize the plant cell wall lignification process. The application of click chemistry in lignocellulose has been very few, there is much more to do. Because click reaction condition is mild so that many reactions can be conducted at room temperature, it is very conducive to the research in the field of biomedical materials. What is more, cellulose and hemicellulose has good biocompatibility so that favorable conditions are created for the application of cellulose and hemicellulose in the biological field. In addition, copper-free click reactions may be as an important development direction due to the toxic effects of copper catalyst, such as strain-promoted alkyne-azide cycloaddition reaction, Thiol-Ene/Yne click reaction and Diels-Alder click reaction.

Key words: click chemistry, cellulose, hemicellulose, lignin