Conversion of technical lignin into performance biopolymers such as polyurethane offers environmental and economic advantages when combined with production of biofuels from biomass sugars, presenting significant interest toward studying the role of pretreatment on lignin structure and functionality. Co-solvent enhanced lignocellulosic fractionation (CELF) pretreatment, employing acidic aqueous tetrahydrofuran (THF) mixtures, was developed to effectively break down the lignin-carbohydrate matrix and promote extraction of lignin from lignocellulosic biomass with desirable purity and yield. In this study, we report the effects of CELF pretreatment reaction severity on the molecular structure of CELF-extracted lignin and its impact toward the mechanical properties of the resulting lignin-based polyurethanes. Reaction temperature was found to play the most significant role, compared to reaction time and acidity, in manipulating structural features such as molecular weight, functionality and intra-polymer structure. At the severe reaction conditions at 180°C, the order of reactivity for primary lignin interlinkages characterized by semiquantitative HSQC NMR analysis were found to be β-ether > phenylcoumaran (β−5′) > resinol (β−β′) facilitating a high degree of depolymerization and yielding a high frequency of free phenolics and reduced aliphatic hydroxyl groups. All side-chain interlinkages were depleted converting guaiacyl subunits into condensed forms, while still retaining uncondensed syringyl subunits. Under the mild 150°C temperature reaction, CELF lignin had higher molecular weight and retained more β-ether interlinkages. The results from CELF lignin-based polyurethane synthesis indicated that the tensile properties depended on the miscibility of CELF lignin with other components and low molecular weight cuts improved the dispersion of lignin in the polyurethane network. Pre-mixing of CELF with poly(ethylene glycol) (PEG) reduced the brittleness and improved the ductility of the CELF lignin-PEG polyurethanes.

当将木质素技术转化为功能性生物聚合物（如聚氨酯）与由生物质糖生产生物燃料相结合时，具有环境和经济优势，对研究预处理对木质素结构和功能的作用表现出极大的兴趣。开发了使用酸性含水四氢呋喃（THF）混合物的共溶剂增强木质纤维素分级分离（CELF）预处理，以有效分解木质素-碳水化合物基质并促进木质素从木质纤维素生物质中提取，并具有所需的纯度和收率。在这项研究中，我们报告了CELF预处理反应强度对CELF提取的木质素分子结构的影响及其对所得木质素基聚氨酯机械性能的影响。与反应时间和酸度相比，发现反应温度在控制诸如分子量，官能度和聚合物内结构的结构特征方面起着最重要的作用。在180°C的苛刻反应条件下，发现以半定量HSQC NMR分析为特征的伯木质素相互连接的反应顺序为β-醚>苯基香豆素（β-5'）>树脂醇（β-β'），促进了高解聚度，并产生高频率的游离酚和还原的脂肪族羟基。所有侧链互连都被消耗，将愈创木脂基亚单位转化为缩合形式，同时仍保留未缩合的丁香基亚单位。在温和的150°C温度反应下，CELF木质素具有较高的分子量，并保留了更多的β-醚交联键。基于CELF木质素的聚氨酯合成结果表明，拉伸性能取决于CELF木质素与其他组分的混溶性，低分子量馏分提高了木质素在聚氨酯网络中的分散性。CELF与聚（乙二醇）（PEG）的预混合可降低CELF木质素-PEG聚氨酯的脆性并改善其延展性。