纤维素纳米晶体膜及胆甾型液晶图案的制备

摘要

以微晶纤维素为原料,采用硫酸水解法制备了纤维素纳米晶体悬浮液,再通过室温下自然干燥的方法制备了纤维素纳米晶体薄膜.通过扫描电子显微镜、紫外可见分光光度计和偏光显微镜,分别研究了纤维素纳米晶体薄膜的光学性能、内部微观结构以及纤维素纳米晶体悬浮液的光学织构变化.研究结果表明,在质量分数64％硫酸、45℃条件下,水解微晶纤维素2h后可制得稳定的纤维素纳米晶体悬浮液;超声处理后的悬浮液可形成胆甾型液晶相,随着悬浮液浓度的变化,通过偏光显微镜可以观察到胆甾型液晶的圆盘织构、条纹织构以及特征指纹织构;超声处理后悬浮液制备的纤维素纳米晶体彩色薄膜具有胆甾型液晶结构;利用偏光显微镜观察到的胆甾型液晶纹理和色彩图案具有防伪性能,可将它们制成具有唯一性的防伪标签.%Microcrystalline cellulose,a kind of straight chain polysaccharide connected byβ-1,4 glycosidic bonds,is an emerging cellulose functional material (with degree of polymerization less than 4 000).For cellulose fiber from plant,crystalline cellulose accounts for about 70％,and the rest is the amorphous cellulose.In this paper,cellulose nanocrystal suspension was prepared through sulfuric acid hydrolysis by using microcrystalline cellulose as raw material.Cellulose nanocrystal film was dried in air at room temperature.The internal microstructure and the optical property of cellulose nanocrystal solid films were characterized by scanning electron microscopy (SEM) and UV-vis spectrophotometer,respectively.Polarized optical microscopy was used to analyze the changes in optical texture of cellulose nanocrystal suspension.The results showed that stable cellulose nanocrystal suspension can be achieved by hydrolyzing microcrystalline cellulose with 64％ mass ratio of sulfuric acid for 2 h at 45℃.Cellulose nanocrystal suspension can form cholesteric liquid crystal phase through ultrasonic treatment.As the concentration of the suspension changed,the disk texture,stripe texture and the characteristic fingerprint texture of the cholesteric liquid crystal could be observed by polarized optical microscopy.Cellulose nanocrystal solid film prepared from cellulose nanocrystal suspension without ultrasonic process showed colorless,but the solid film prepared with ultrasonic treatment was a colorful film with cholesteric liquid crystal structure.The SEM image of the solid film showed that the arrangement of the cellulose nanocrystals within the colorless solid film was disordered,while the cellulose nanocrystals within the colorful solid film formed ordered layers which had cholesteric liquid crystal structure.The texture pattern and color pattern of cholesteric liquid crystal observed by polarized optical microscopy had anti-fake performance and could be made into unique texture and color used for anti-counterfeiting labels.