纳米纤维素基导电复合材料研究进展

Advances in Nanocellulose-Based Electroconductive Composites

作为一种天然可再生资源,纤维素及其衍生材料在国民生产中扮演着重要角色。随着纳米科技的发展,利用化学、物理、酶催化等方法得到一维纳米尺度的纳米纤维素应运而生。由于纳米纤维素具有高强度、高表面积、低热膨胀系数、易交织成网状结构等特点,其作为基体材料在柔性屏幕、透明传感器及储能器件方面发展迅速。按照制备方法(机械法、氧化法、水解法)的不同,可以得到具有不同物理微观形态和化学修饰基团的2类纳米纤维素:纳米纤维素纤丝和纳米纤维素晶体。按照储能机制的不同,导电活性物质主要包括导电高分子(聚吡咯、聚苯胺等)、金属氧化物(二氧化锰、二氧化钛、氧化锌等)和碳材料(碳纳米管、石墨烯等)。由于纳米材料形态特征的差异性,纳米纤维素与导电活性物质可以形成不同微观尺度和结构特性的导电复合材料。在研究领域上,导电高分子/纳米纤维素基导电复合材料主要用于电致变色器件、电化学传感器及驱动器、超级电容器等研究领域,尤其是作为赝电容的超级电容器,表现出更出色的比电容;碳材料与纳米纤维素形成的导电复合材料,可作为柔性电极用于柔性电池、柔性超级电容器等电子器件领域;金属氧化物其纳米粒子具有独特的磁性、光学、压电等性能,其纳米纤维素复合材料在光电材料、太阳能电池等领域具有应用价值。正是由于纳米纤维素具有易于成膜与凝胶化、高吸水性、溶胀性、生物相容性等特性,才可以作为结构稳定与机械性能优良的载体材料或者骨架支撑材料,并与各类无机或有机纳米材料的特定导电性能相互融合在一起,进而产生具有高导电性、光电转换性、电化学氧化还原特性的特殊功能材料。在制备方法上,导电高分子不但可以通过溶液分散与纳米纤维素形成导电膜材料,而且可以通过原位聚合方式得到导电高分子/纳米纤维素导电复合材料;而棒状的碳纳米管、片状的石墨烯以及颗粒状的金属氧化物主要是通过溶液分散方法在纳米纤维素中形成稳定溶液或水凝胶,进一步通过溶剂挥发、过滤、冷冻干燥或超临界干燥等方法得到导电性良好的薄膜材料或者气凝胶材料,还可以通过层层自组装技术得到透明导电膜材料。纳米纤维素在柔性电子储能器件上尚有较大发展潜力,下一步应针对纳米纤维素与导电材料之间的复合方式、分散均匀性、微结构控制、界面相容及相互作用机制等方面开展深入研究,更大限度地发挥纳米纤维素在导电活性物质上的平台效应,为纳米纤维素的功能化与应用提供更多的研究思路。

As a natural renewable resource material,cellulose and its derivatives play an important role in the national production. With the development of nano-technology, one-dimensional nano-scale nanocellulose has emerged by chemical,physical and enzymatic methods. As a matrix material,nanocellulose has a rapid development in the field of flexible,transparent terms of screens,sensors and storage devices because of its property of high strength,high surface area,and low thermal expansion coefficient and easily woven into a mesh structure. According to the different preparation methods（ mechanical,oxidation and hydrolysis method）,it can be got two types of nanocellulose with different physical morphology and chemical modification group,that is cellulose nanofibrils and cellulose nanocrystals. According to different storage mechanisms,the conducting electroactive materials include conductive polymer（ polypyrrole,polyaniline,etc.）,metal oxide（ manganese dioxide,titanium dioxide,zinc oxide,etc.） and carbon materials（ carbon nanotubes,graphene,etc.）. Because of the morphology differences of nanomaterials,nanocellulose and the conducting electroactive materials can be formed of electroconductive composites with different micro-scale and structural characteristics. In the research field,the conducting polymer / nanocellulose electroconductive composites are mainly used for electrochromic devices,electrochemical sensors,drive,and supercapacitors,especially for the pseudo-capacitance supercapacitors with better capacitance. Electroconductive composites combined nanocellulose with carbon nanotubes and graphene can be used as a flexible electrode for flexible batteries,and flexible supercapacitors. Metal oxide nanoparticles have unique magnetic,optical and piezoelectric properties,thus the metal oxide nanoparticles / nanocellulose electroconductive composites can be used for photovoltaic materials and solar cells. As the carrier material or skeleton supporting material with excellent structural stability and mechanical properties, nanocellulose could combine with a variety of inorganic or organic conductive nanomaterial to produce special functional materials with a high conductivity,photoelectric conversion and the electrochemical oxidation-reduction characteristics. This is because nanocellulose is liable to form film and gel and has good characteristics of high water absorption,swelling and biocompatibility. From the progress of the preparation method,conductive polymer not only can be used to form a conductive film material by dispersing it into the solution of nanocellulose, but also to obtain the conductive polymer / nanocellulose electroconductive composites by in-situ polymerization methods. Carbon nanotubes,graphene sheet and a particulate metal oxide can be mainly formed to a stable dispersion or hydrogel by dispersing them into the solution of nanocellulose,and further to obtain a film or aerogel material with good conductivity by solvent evaporation,filtration and freeze-drying or supercritical drying. They can also form a transparent conductive film material by the layer-by-layer self-assembly technology. There are large development potential of nanocellulose in the flexible electronic storage devices. In the future,the complex way,uniformity of dispersion,microstructure control, interface compatibility and interaction mechanism between nanocellulose and conducting electroactive materials will be studied deeply and play the role of nanocellulose platform for conducting electroactive materials further. Hope this review could provide some research ideas for further function and application research of nanocellulose.