Here we report the synthesis of thermosetting resins from low molar mass Kraft lignin fractions of high functionality, refined by solvent extraction. Such fractions were fully characterized by 31P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description of the structures. Reactive oxirane moieties were introduced on the lignin backbone under mild reaction conditions and quantified by simple 1H NMR analysis. The modified fractions were chemically cross-linked with a flexible polyether diamine ( Mn ≈ 2000), in order to obtain epoxy thermosets. Epoxies from different lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated substantial differences in terms of thermo-mechanical properties. For the first time, strong relationships between lignin structures and epoxy properties could be demonstrated. The suggested approach provides unprecedented possibilities to tune network structure and properties of thermosets based on real lignin fractions, rather than model compounds.

中文翻译：

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基于分馏和充分表征的木质素的可调热固性环氧树脂

在这里，我们报告了从高官能度的低摩尔质量牛皮纸木质素部分合成热固性树脂，并通过溶剂萃取精制。这些馏分通过 31 P NMR、2D-HSQC NMR、SEC 和 DSC 进行充分表征，以获得结构的详细描述。在温和的反应条件下，将反应性环氧乙烷部分引入木质素主链上，并通过简单的 1 H NMR 分析进行量化。改性部分与柔性聚醚二胺 (Mn ≈ 2000) 进行化学交联，以获得环氧热固性材料。通过 DSC、DMA、拉伸试验和 SEM 研究的来自不同木质素组分的环氧树脂在热机械性能方面表现出显着差异。首次证明了木质素结构与环氧树脂性能之间的密切关系。