基于低共熔溶剂预处理的高分散性木质纤维素纳米纤丝的制备及调控机制研究

In terms of the current issues that the pretreatment has the problems of high cost and pollution to the environment, and poor dispersibility of cellulose nanofibril (CNF) in the production process, a creative idea that Deep Eutectic Solvent (DES) systems based on sulfamic acid and urea are used as sulfation pretreatment for cellulose nanofibril production to improve the dispersibility of CNF and broaden its applications. Eucalyptus pulp will be used as the raw material, sulfamic acid and urea will be used to prepare the DES in this project. Experiments will be carried out with DES pretreatment under different conditions, changes in the main components of fiber, the microphysical and chemical structure and functional groups of cellulose will be investigated by modern instrument analysis (AFM, GC-MS, etc). By these means, we can understand the interaction mechanism between the DES systems and the fiber component and structure-activity relationship. Furthermore, combined with subsequent mechanical treatment, we can clarify the influence mechanism of pretreatment of DES system on nanofibrillation process and CNF properties. In addition, the control of the energy consumption during the CNF preparation process, the structural features, the chemical composition and the surface properties of CNF in DES pretreatment will be achieved. The present research will provide theoretical guidance for the preparation of CNF by pretreatment of DES system based on sulfamic acid and urea, and new ideas for the green and efficient preparation of nanofibers. Moreover, the present research will enrich the theoretical system of related pretreatment in the process of preparing CNF by mechanical method.

针对纤维素纳米纤丝(CNF)制备过程中存在的预处理成本高、对环境产生污染、CNF产品分散性差等问题，提出采用新型绿色低共熔溶剂(DES)对纤维进行预处理，以降低CNF制备成本，提高其分散性能，拓宽其应用范围。本项目以桉木浆为纤维原料，采用氨基磺酸/尿素DES，在不同条件下对纤维原料进行磺化改性预处理，采用AFM、GC-MS等现代仪器分析DES预处理过程中纤维原料主要组分及纤维素的微观物理化学结构和功能基团的变化，了解DES体系与纤维组分之间的相互作用机制及构效关系，并根据后续机械法纤维纳米化处理过程的参数变化，阐明DES体系预处理对纳米纤丝化过程及CNF性能的影响机制，实现CNF制备能耗、结构特征、化学组成及表面性能的有效控制。研究结果可为氨基磺酸/尿素DES体系用于高分散性纳米纤维素制备过程提供理论指导，进而丰富机械法制备CNF科学理论体系，为绿色高质量制备纳米纤维素提供新思路。

本项目以杨木漂白硫酸盐为原料，研究了采用氨基磺酸基低共熔溶剂（DES）下纤维素纳米纤丝（CNF）的制备，以及机械法结合氢键阻滞剂体系对CNF再分散性能的影响。探究了DES对纸浆纤维原料的润胀、结晶度、纳米化过程中能耗和CNF稳定性的影响，探究了不同氢键阻滞剂及不同干燥方式对CNF再分散性能的影响，探究了氯化钠预处理组合真空干燥与冷冻干燥对对CNF再分散性的影响，以及氯化钠与氯化钾作预处理组合喷雾干燥对CNF再分散性能的影响。研究发现DES预处理能够润胀纤维，纤维表面出现分丝帚化现象，DES预处理时间从1.0 h到1.5 h，DES处理后的纸浆纤维长度减小，纤维直径和取代度增大，最大取代度为0.17，DES预处理后的CNF的平均粒径减小，平均粒径最小为40.02 nm，Zeta电位的绝对值增大，胶体稳定性提高，结晶度下降，CNF悬浮液的稳定性提高。DES预处理降低了CNF的热稳定性，DES预处理可明显降低纤维原料在均质过程中的能耗，均质处理15次时能耗可降低43.9%。在改善CNF再分散性能方面，氯化钠起到了“氢键阻滞剂”的作用，而且真空干燥方式对氯化钠阻滞作用的增强效果好于冷冻干燥方式，真空干燥得到的CNF结晶度低，而且其水溶液再分散稳定性高。真空干燥的CNF的平均粒径小于冷冻干燥的CNF。FTIR和EDX分析结果表明，悬浮液的pH值为8时，真空干燥更有利于钠离子与羧基及羟基的络合，有利于CNF的再分散。经过真空干燥处理的CNF的稳定性指数（TSI）低于冷冻干燥处理的CNF，表明经过真空干燥处理的CNF再分散后的稳定性优于经过冷冻干燥处理的CNF。经过KCl预处理组合喷雾干燥制备的CNF的平均粒径小于经过NaCl预处理的的CNF。EDX分析表明，钾离子更容易与羧基、羟基络合，有利于防止CNF在干燥过程中不可逆团聚现象的发生，使干燥后的CNF粉末更容易在水溶液中再分散。经过KCl预处理的CNF的稳定性指数（TSI）值低于经过NaCl预处理的CNF，经过KCl预处理的CNF再分散后的稳定性优于经过NaCl预处理的CNF。KCl预处理有利于降低CNF在干燥过程中的不可逆团聚现象。