木素-碳纤维相演化中结构缺陷识别及其缺陷调控对预氧化分子环构化影响机制

Utilization of the lignin generated from cellulosic ethanol industry residue has become a key issue in the future development of cellulosic ethanol industry. Lignin has almost been recognized as the best natural polymer to substitute petrochemical feedstocks to produce carbon fibers because of its advantages of renewability, low cost and high carbon content. However, the structure inadaptability of the lignin itself during the key stage of pre-oxidation stage of lignin-to-carbon fiber phase evolution has become a bottleneck constraining the development of high strength lignin-based carbon fiber. Cellulosic ethanol industrial lignin is used as raw material in this project. The research focuses are recognizing lignin structural defects and improving lignin adaptability to molecular cyclization in pre-oxidation stage through regulation of structural defects. The targeted feedback is the degree of structural defects carry-over in all phase evolution stages and carbonization behavior. Lignin structural defects such as wide distribution of molecular weight, active groups containing oxygen and so on, are regulated, and the influence of the regulation on planar trapezoid structure formation through molecular cyclization is determined. The complete response mechanism of “Recognition of lignin structural defects-Regulation of structural defects—Molecular cyclization in pre-oxidation stage-High strength lignin-based carbon fiber” will be established, which will provide theoretical support for breaking the bottleneck of the structure inadaptability of the lignin itself constraining high strength lignin-based carbon fiber preparation.

如何利用纤维素乙醇工业残渣中的木素，已成为纤维素乙醇产业发展的关键问题。木素因其可再生、廉价、含碳量高等优点几乎成为替代石油基原料生产碳纤维最理想的天然聚合物，但其自身结构对木素-碳纤维相演化关键阶段（预氧化阶段）的不适性已成为制约高强度木素基碳纤维的瓶颈。本课题以纤维素乙醇工业残渣木素为原料，以木素中不适性结构缺陷识别及缺陷调控改善木素对预氧化阶段分子环构化适应性为研究重点，以相演化各阶段缺陷遗留程度与碳化行为为目标反馈，拟明确木素分子量分布、含氧活性基团等缺陷结构调控对预氧化阶段分子环构化形成规则二维梯形平面结构影响机制，构建“木素结构缺陷识别—缺陷调控—预氧化阶段分子环构化—高强度碳纤维”完整应答机制，为打破木素自身结构对高强度木素基碳纤维制备的不适性瓶颈提供基础理论依据。

随着化石燃料资源的短缺和环境保护的日益重视，传统的、不可再生资源正有被可再生资源所取代趋势。在全球范围内，木质素作为自然界中储量仅次于纤维素的第二大可再生资源，已经受到人们越来越多的关注。由于其独特的化学结构和性质（高含碳量，大量的芳香结构，较好的热稳定性）使其成为生产碳纤维的替代原料。然而，由于木质素结构的复杂性且分子量分布不均一等原因，阻碍了木质素的发展和应用。本项目围绕秸秆纤维素乙醇残渣木素制备碳纤维相演化过程中木素自身结构缺陷识别与调控对分子环构化行为影响关键科学问题。开展了不同结构在碳纤维演化各阶段转化机制研究，识别木素结构中存在的缺陷及缺陷结构在碳纤维演化各阶段的缺陷遗留程度。通过对木素分级提取获得含有不同活性官能团、不同分子量、不同玻璃化转化温度、不同元素含量的木素。以所获的木素为原料进行碳纤维制备，通过对木素-碳纤维相演化过程工艺差异及相演化各阶段结构特征识别，分析木素自身结构对木素-碳纤维相演化的适应性。开展了木素分子量多分散性的缺陷调控研究，明确木素分子量调控对纺丝液理化性质及预氧化分子环构化分子量影响行为，解决木素分子量多分散性缺陷遗留造成的环构化程度不均匀及碳化性能差等问题。采用木素自身分子量分级提取和接枝共聚构建超高分子量木素两种方式进行分子量缺陷结构调控。开展了木素中含氧活泼性基团（如羟基、羧基等）缺陷结构调控研究，构建含氧活泼性基团对预氧化阶段环构化影响机制。通过化学修饰改变羟基（羧基）位端活泼性研究其对预氧化阶段可控性及碳化阶段碳纤维表面粘结行为影响机制，为缺陷结构调控增强木素对木素-碳纤维相演化过程的适应性提供理论基础。