柔性透明衬底材料设计及生物质自增强全纤维素的溶解再生和结构调控研究

Improving the comprehensive performance, including optical, thermal, mechanical and moisture-resistance properties, etc, of flexible and transparent substrate is one of the key issues for the development of advanced flexible electronic technologies, such as e-paper. This project will utilize the biomass (including bacterial, wood or shellfish) cellulose nanofibers to produce high performance self-reinforced all-cellulose, i.e. cellulose nanofiber/regenerated cellulose composite system, by the control methods of dissolution followed by regeneration, then with the structure-control methods, self-reinforced all-cellulose/resin composites with high optical transparency, low coefficient of thermal expansion, high flexibility, and low moisture absorption rate will be designed. This project will also explore the suitable ratio of biomass cellulose dissolution and the corresponding control methods of dissolution and regeneration, analyze the relationship between the properties of self-reinforced all-cellulose and the control on the structure-change of macromolecular and unit cell in the self-reinforced all-cellulose, and then investigate the influence mechanism of dissolution and regeneration on the properties of self-reinforced all-cellulose. This project will then study the influence of structure-control methods, such as structure-softening, surface-modification structure, etc, of self-reinforced all-cellulose on the properties of self-reinforced all-cellulose/resin composites, and investigate the influence mechanism and law of structure-softening molecules on the interface of self-reinforced all-cellulose. This project designs novel weather-resistible and applicable self-reinforced all-cellulose/resin composites by effectively combining the technology of biomass cellulose dissolution and regeneration, self-reinforced all-cellulose/resin composite technology and flexible electronic technology, which will supply a new idea for obtaining high-performance flexible and transparent substrate materials.

提高柔性透明衬底的光、热、力、湿等综合性能是电子纸等先进柔性电子技术发展的核心问题之一。本项目利用生物质(细菌、木材、甲壳动物)纤维素纳米纤维，通过溶解再生调控，获得自增强全纤维素(即纤维素纳米纤维/再生纤维素体系)；再通过结构调控，设计出具高透明度、低热膨胀率、高柔性和低吸湿性的自增强全纤维素/树脂复合材料。并探索纤维素纳米纤维溶解再生适宜比例及其配套溶解再生调控方法，分析自增强全纤维素中大分子、晶胞的结构变化控制与性能的关系，探讨溶解再生对自增强全纤维素性能的影响机理。研究自增强全纤维素的结构增柔和表面改性结构等结构调控方法对复合材料性能的影响，探讨结构增柔分子对自增强全纤维素内界面的影响机理和规律。该项目将生物质纤维素纳米纤维溶解再生技术、自增强全纤维素/树脂复合材料技术与柔性电子技术结合起来，设计新型耐候适应型自增强全纤维素/树脂复合材料，为获得高性能柔性透明衬底材料提供新的思路。

柔性电子是当前科学技术最前沿研究领域之一，涵盖RFID、柔性显示、柔性光伏、可穿戴设备等诸多应用，是国家重要战略新兴产业。发展先进柔性透明衬底材料是柔性电子技术发展的核心问题之一。本项目将生物质纤维素纤维溶解再生技术、全纤维素复合材料技术与柔性电子技术有机结合在一起，围绕先进柔性电子技术对衬底性能的特殊需求，深入研究了生物质纤维素纤维溶解再生适宜比例及其配套溶解再生调控方法，分析了再生纤维素膜结构和性能及孔洞等缺陷的控制方法及其对全纤维素复合体系性能的影响，研究了全纤维素体系基质结构增塑和表面改性结构对全纤维素/树脂纳米复合材料性能的影响，设计和制备了全纤维素/树脂纳米复合材料用于超薄柔性透明衬底。研究表明通过控制N-甲基吗啉-N-氧化物等溶剂的浓度和溶解时间可以使生物质细菌纤维素的溶解过程发生在可控范围内，实现对溶解再生比例的控制。制得的再生生物质细菌纤维素膜和部分溶解再生的全纤维素复合膜进行了X射线衍射和傅氏转换红外线光谱分析仪等显微观察和结构分析，运用紫外可见光光谱仪、热机械分析仪、万能材料试验机等进行了性能测试，结果表明溶解再生后晶体结构由纤维素I型向纤维素II型转变，-OH基团含量增高；而全纤维素复合膜仍保留有部分纤维素I型的结构，-OH含量明显高于原细菌纤维素膜。不同再生浴种类对再生生物质细菌纤维素膜的可见光区透光率有影响，利用50%甲醇水溶液再生浴可达到透光率近 90%。研究发现全纤维素复合膜透光率较低，通过与透明树脂复合，透光率由21%升高至73%。全纤维素复合膜与原细菌纤维素膜相比，综合性能得到全面提高，热膨胀系数、杨氏模量和吸湿率分别由7.6 ppm/K（293-423K）、4.9GPa和99.1%（293K,RH55%)）降至1.7ppm/K（293-423K）、2.1GPa和0.84%（293K, RH55%），拉伸强度由17.2微降至15.8MPa。将全纤维素膜(47vol.%)与2-乙基已基丙烯酸酯改性环氧树脂复合，树脂透光率损失<6%；但CTE降低至2.2ppm/K（293-423K）、杨氏模量达到12.3GPa、吸湿率0.62% (293K, RH55%)、拉伸强度256MPa。利用纳米石墨微片提高细菌纤维素基体导电性，最高导电率达到4.5S/cm。本项目研究成果为具国际竞争力的新型柔性电子衬底材料开发提供了理论基础和核心材料技术。