The challenges in high value-added utilization of lignin own to its wide molecular weight distribution and complex physicochemical properties associated with it. How to narrow the molecular weight of lignin and elucidate the differences in physiochemical properties related to molecular weight of lignins is of crucial importance for lignin conversion processing. In this study, lab-made Kraft and ethanol lignins were fractionated into several narrower molecular weight distribution components through a designed solvent system. The yield, molecular weight distribution, structural characterization and their physicochemical properties of each fractionated lignin were analyzed comparatively. The results indicated that the yield of ethanol lignin is higher (8.44 %) than that of Kraft lignin (5.26 %). Kraft lignin shows lower molecular weight (Mw=2480 g/mol), higher hydroxyl content (4.29 mmol/g), and lower content of β-O-4 and β-5 bonds compared to ethanol lignin (Mw=3682 g/mol, 2.10 mmol/g). Meanwhile, the phenolic hydroxyl content in both ethanol and Kraft lignins increased with the decrease of molecular weight. Furthermore, ethanol lignin demonstrated higher antioxidant activity and much higher (65times) tensile strength of lignin-based polyurethane elastomer than that of Kraft lignin-based polyurethane elastomer.

中文翻译：

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乙醇与杨树牛皮木质素连续溶剂分馏法制备木质素理化特性的比较研究及其应用


木质素高附加值利用的挑战在于其广泛的分子量分布和与之相关的复杂物理化学性质。如何缩小木质素的分子量并阐明与木质素分子量相关的理化性质差异对于木质素转化过程至关重要。在本研究中，通过设计的溶剂系统将实验室制备的牛皮纸和乙醇木质素分离成几种分子量分布较窄的组分。对比分析了每种分级木质素的产量、分子量分布、结构表征及其理化性质。结果表明，乙醇木质素的收率 （8.44 %） 高于牛皮纸木质素 （5.26 %）。与乙醇木质素相比，牛皮纸木质素表现出较低的分子量 （Mw=2480 g/mol）、较高的羟基含量 （4.29 mmol/g） 以及较低的 β-O-4 和 β-5 键含量 （Mw=3682 g/mol， 2.10 mmol/g）。同时，乙醇和牛皮木质素中的酚羟基含量均随着分子量的降低而增加。此外，与牛皮纸木质素基聚氨酯弹性体相比，乙醇木质素基聚氨酯弹性体表现出更高的抗氧化活性和远高于木质素基聚氨酯弹性体的拉伸强度（65 倍）。