残渣木质素液化机理及其产物对聚氨酯材料性能调控机制研究

Polyurethanes have been widely used in various fields of the national economy. The residues from bioethanol production processes have great potential for developing lignin based polyurethane to reduce the utilization of petrochemical products due to its properties of renewability, cheap, non-toxic etc. This project will focus on the major difficulties in the structural elucidation, liquefaction mechanism and value-added conversion of lignin. The industrial lignocellulosic residues in China will be chosen as raw materials, the structures of residual lignin will be qualitatively and quantitatively characterized by high-resolution liquid NMR techniques. The structural characteristic of the residual lignin in the liquefaction process will be studied through lignin model compounds, and the liquefaction modification mechanism of the residual lignin will be explored based on this. The regulation mechanism of the structural properties of the liquefied products on the performance of polyurethane rigid foam will be explained. In addition, the relationship between the structural features of the residual lignin modified by liquefaction and the performance of the polyurethane rigid foam can also be established. At last, this project will construct a unified system of lignin structure, liquefaction modification mechanism and polyurethane properties. Prospective results of this project will provide theoretical guidance and technical support for the value-added utilization of the lignocellulosic residue from bioethanol industry.

聚氨酯是一种广泛应用于国民经济领域的高分子材料，纤维素乙醇工业中木质纤维残渣由于资源可再生，绿色无毒害等诸多优点，在替代化工原料制备聚氨酯材料方面具备很大潜力。本项目针对木质素结构定量表征、液化改性机理及高值化利用时存在的研究重点及难点，拟选用我国大宗的木质纤维残渣为原料，采用高分辨液体核磁技术定性定量地研究残渣木质素的分子结构特点；重点通过木质素模型物研究残渣木质素液化改性过程中组分和结构特性的变化规律，揭示残渣木质素液化改性反应机理；阐明残渣木质素液化产物结构特性对聚氨酯硬泡材料特定性能的调控机制，建立其液化改性产物结构特性与聚氨酯硬泡性能之间的构效关系，最终构建结构与性能统一的“木质素结构—液化改性机理—聚氨酯材料性能”关联系统。本项目预期成果将为纤维素乙醇工业中木质纤维残渣的高值化利用提供理论指导和技术参考。

本项目利用2-甲基四氢呋喃/水两相绿色体系分离木质素，研究了路易斯酸催化剂和预处理温度对木质素得率和纯度的影响。研究结果显示，基于AlCl3催化2-甲基四氢呋喃/水两相体系分离得到的木质素，得率高达18.1%。随着温度的升高，木质素的得率逐渐增加，分子量先逐渐减小，但在180 oC时其分子量显著增加，并且具有典型阔叶木木质素结构特征，β-O-4相对含量较高。因此，基于AlCl3催化2-甲基四氢呋喃/水两相体系可以作为一种有效分离木质素的方法。以纤维素乙醇工业中残渣木质素为研究对象，基于多元醇基低共熔溶剂体系对其进行液化改性，研究了溶剂种类、时间、温度等因素对液化改性残渣木质素的结构和官能团的影响。研究结果表明，残渣木质素破坏了多元醇基低共熔溶剂的有序结构与之形成氢键，液化改性残渣木质素的酚羟基含量明显提高，相对分子量和多分散指数显著下降，其主要结构在液化改性后没有发生显著变化。利用液化改性木质素替代商业聚醚多元醇制备了木质素聚氨酯硬泡材料，研究了木质素替代率对木质素聚氨酯硬泡材料性能的影响。研究结果表明，随着液化改性木质素替代率提升，木质素聚氨酯硬泡材料的表观密度和压缩强度均呈现先增大后减小的趋势，当木质素替代率30%时，最大表观密度和压缩强度分别达到64.13 kg/m3和673 kPa。并且当木质素替代率在58.6%时，木质素聚氨酯硬泡材料的性能仍能满足国家标准GB/T 29288-2012。因此，基于多元醇基低共熔溶剂体系液化改性的残渣木质素可以作为一种制备木质素基聚氨酯材料的有效途径。