基于多级机械剪切剥离宏量制备竹纤维素纳米纤及其聚合物复合材料研究

This proposal focuses on the manufacturing of high value-added cellulose nanofibrils (CNF) from the abundant bamboo resources and developing high performance CNF reinforced polymer composites. The state-of-the-art technologies for mechanical nanofibrillation of plant fibers still have quite a lot of deficiencies, such as high energy consumption, severe degradation of cellulose, sharp decrease of crystallinity, which may deteriorate CNF's properties. To tackle these problems, novel pretreatment technologies coupled with the powerful multi-level mechanical shearing exfoliation equipment will be developed to directly target the hieratical ultrastructure of bamboo cellulose fibers. The morphological and structural alteration of bamboo fibers during pretreatment and multi-level mechanical exfoliation process will be systematically investigated to elucidate the underlying nanofibrillation mechanism. In addition, a one-step extraction and surface modification of CNF, which works under a mechanochemical mechanism, will be proposed to address the dispersing and interface problems when used in polymer composites. High performance polymer/CNF composites will be produced via melt processing. The mixing, dispersing and interface interactions in the composites, the relationship between structure and property of the composites will be studied. The implementation of this proposal is anticipated to generate some new theories and new technologies for large-scale productions of CNF as well as its applications in a large scale, which will ultimately lead to the fast growth of CNF material of our country.

本项目致力于将丰富的竹资源转化成高附加值的纤维素纳米纤（cellulose nanofibrils，CNF），研制竹CNF增强的高性能聚合物复合材料。针对目前机械法制备CNF存在高能耗，纤维素降解、结晶度降低等致使CNF性能下降的问题，根据宏观竹纤维的多层次结构特点，开发新型纤维素预处理技术，并设计制造具有强大剪切和剥离功能的"多级剪切机械剥离"装置。系统研究预处理和多级剪切机械剥离过程中竹纤维结构与形态演变，揭示多级剪切剥离制备竹CNF的机理。针对CNF在高分子复合材料应用中面临的分散问题和界面问题，开发基于力化学原理的一步法制备表面改性CNF的方法,通过熔融加工制备高性能CNF增强的聚合物复合材料。研究CNF在聚合物基体中的混合、分散和界面相互作用及复合材料结构与性能的关系。本项目的实施，将为竹CNF的宏量制备及应用提供新原理和新技术，对促进我国的纤维素纳米材料的发展具有重要意义。

针对目前机械法制备纤维素纳米纤 CNF存在高能耗，纤维素降解、结晶度降低等致使 CNF 性能下降的问题，设计研制了“多级剪切机械剥离”设备，通过4种剪切剥离结构不同的磨盘的组合，有效解决了目前机械法制备 CNF 存在的易堵料、处理量小、能耗高的难题，强化了剪切力改变纤维素的超分子结构的作用，实现CNF间氢键高效解缔制备CNF。与传统的单级剪切粉碎设备对比，产能提高了5倍以上，能耗降低了60%以上。项目进一步研究了DMAc/LiCl和TEMPO等多种纤维素预处理新方法，通过超声波辅助-机械剪切剥离结合的方法，大幅度提高了CNF的剥离效率，制备了直径分布均一（约25 nm）；结晶度高，耐热性能和分散性良好的CNF。本项目建立的“多级剪切机械剥离宏量制备竹浆纳米纤维素”技术与制备已经与企业开展产学研合作，正在进行年产1000吨CNF的生产线建设。. 本研究创新提出了多种CNF表面改性和复合技术，研究CNF在聚合物基体、氧化石墨烯、丝素蛋白纳米纤维、无机纳米粒子等的分散复合，设计制备了多种高性能储能材料、自供电器件、高性能高效分离材料和聚合物/CNF纳米复合材料；利用纤维素纳米纤维（CNFs）和丝素蛋白（SF）通过模板诱导自组装形成有序-无序交替的SF/CNF纳米薄膜（厚度50-100nm），利用SF的高粘结性能强化 CNF 网络结构连接点，制备了高强度高模量的SF/CNF纳米薄膜，其最大应力和杨氏模量分别为 260 MPa和30 Gpa，远高于目前报道的CNF或者SF基聚合物复合材料，是目前所报道的最强的生物材料之一。本研究为利用纯天然材料设计和制备高性能功能性纳米薄膜提供新思路，具有重要的理论价值和应用前景。