木质素的线型化结构构筑及其熔融离心纺丝成形机理研究

Lignin, as a kind of renewable and low-cost material with high carbon content, attracts much attention from researchers. However, its complex structure, strong hydrogen bonding and π-π interaction lead to a poor spinnability and a low strength of obtained fibers, which largely limit its further application in the field of melt-spun precursor. This project is aimed at realizing the controllable preparation of melt-spun lignin micro-nanofibers via structure analysis, purification process design, chemical structure re-construction and melt centrifugal spinning process. The structure-activity relationships between chemical structure and melt spinnability of lignin are systematically investigated. Based on this, linear or slightly–crosslinked lignin macromolecules used for melt centrifugal spinning are constructed to take advantage of small size effect and synergistic effect of each structural unit. In combination with purification process and structure design, the tailoring and re-construction of lignin structure are achieved. The constitutive equation of melt centrifugal spinning process is established after detailed discussion on the influences of incorporated chemical structure and chain length on the rheological property, aggregation structure and spinnability of modified lignin. Evolutions of aggregation structure, microstructure and chemical structure of lignin during melt centrifugal spinning process are clarified to reveal the intrinsic relationships among chemical structure, processing parameters and its fiber properties. Melt-spun lignin micro-nanofibers with high orientation and good properties are expected to prepare through the research of this project, providing fundamental basis for further expansion in precursors of carbon micro-nanofibers.

木质素由于具有资源可再生、价格低廉、碳含量高等优点而颇受关注，然而其结构复杂、分子间氢键和π-π相互作用强，导致其熔融可纺性差、所得纤维强度低，极大限制了其在熔纺前驱体纤维中的应用。为此，本项目拟从木质素的化学结构出发，通过结构解析、分离与纯化，化学结构重构和熔融离心纺丝成形实现其熔纺微纳米纤维的可控制备。系统研究化学结构与熔融离心可纺性间的构效关系，构筑成纤用“线型/微交联”木质素大分子，发挥各结构单元的小尺寸效应和协同效应，实现其分子结构的“剪裁”和“组装”。深入探讨引入分子结构和链长对其流变性能、聚集态结构及可纺性的影响规律，建立描述其熔融离心纺丝成形的本构方程，揭示纺程中聚集态结构、微观结构和化学结构的演变历程，阐明纤维性能与其结构和成形工艺间的内在联系。通过本项目的研究，有望得到取向高、力学性能优良的熔纺木质素微纳米纤维，为进一步拓展其在微纳米碳纤维前驱体中的应用提供理论基础。

木质素是自然界中一类具有芳香族结构的有机高分子，其含量仅次于纤维素。然而木质素结构复杂，极大限制了其高附加值产品的开发，绝大部分被直接燃烧用于发电，有效利用率极低。实现造纸副产物木质素向高附加值产品的转化，对减少环境污染，提高资源利用率具有重要的意义。将木质素经纺丝成形、预氧化和碳化后制备木质素基微纳米碳纤维成为提高其附加值的有效途径。然而木质素化学结构与纤维可纺性及性能间的关系尚不清楚，针对该问题，本项目聚焦于木质素化学结构与聚集态结构和纤维性能间的构效关系，通过结构解离、纯化工艺设计、化学结构重构、纺丝成形及外场调控等方法得到了性能优良的木质素基微纳米纤维及其碳纤维。系统研究了结构组分、可纺性及纤维性能间的内在关系，深入探讨了分子结构、引入单元对木质素基微纳米碳纤维聚集态结构的影响规律，揭示了木质素基微纳米碳纤维制备过程中聚集态结构、微观结构和化学结构的演变历程，初步归纳出熔纺成纤用木质素的化学结构特点，并探索了木质素基微纳米碳纤维在柔性压阻传感器和超级电容器中的应用。主要得到以下结论：. （1）提出Kraft硬木木质素为“线型”结构，经纯化工艺设计和熔纺成形后得到了连续化卷绕的木质素纤维，并进一步经预氧化和碳化后得到低成本木质素基碳纤维；. （2）对比研究了化学结构对木质素基微纳米碳纤维微晶结构等的影响，提出木质素的交联结构更有利于石墨微晶结构的形成，初步拓展了木质素基微纳米碳纤维在柔性压阻传感器中的应用；. （3）阐明了分子量与木质素基微纳米碳纤维微晶结构间的构效关系，指出高分子量的木质素易于形成类石墨结构，而低分子量的木质素则倾向于形成无定形碳；. （4）证实氢键作用有利于石墨微晶结构的形成，基于氢键作用实现了木质素基碳纤维聚集态结构和孔洞结构的调控，探索了其在柔性超级电容器领域中的应用。