To improve the reactivity of lignin for incorporation into high value polymers, the introduction of amines via Mannich reaction is a commonly used strategy. During this functionalization reaction, intra- as well as intermolecular lignin–lignin crosslinking occurs, which can vastly change the elastic properties of the lignin, and therefore, the properties of the resulting polymer. Therefore, the molecular structure of the amine that is used for such a lignin functionalization may be of great importance. However, the relationship between the molecular structure of the amine and the elastic properties of the lignin-based polymer that is generated thereof, has not been fully understood. Herein, this relationship was investigated in detail and it was observed that the molecular flexibility of the amines plays a predominant role: The use of more flexible amines results in an increase in elasticity and the use of less flexible amines yields more rigid resin material. In addition to the macroscopic 3-point bending flexural tests, the elastic modules of the resins were determined on the nanometer scale by using atomic force microscopy (AFM) in the PeakForce tapping modus. Thus, it could be demonstrated that the intrinsic elasticities of the lignin domains are the main reason for the observed tendency.

中文翻译：

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环氧树脂与胺化木质素的共固化：深入了解木质素胺化过程中木质素均交联对弹性性能的作用

为了改善木质素掺入高价值聚合物的反应性，通过曼尼希反应引入胺是常用的策略。在该官能化反应过程中，发生了分子内和分子间木质素-木质素的交联，这可以极大地改变木质素的弹性，并因此改变所得聚合物的性质。因此，用于这种木质素官能化的胺的分子结构可能非常重要。然而，还没有完全理解胺的分子结构与所产生的木质素基聚合物的弹性性能之间的关系。在此，对这种关系进行了详细研究，发现胺的分子柔性起主要作用：使用更具挠性的胺会增加弹性，而使用挠性较小的胺会产生更坚硬的树脂材料。除了宏观的三点弯曲挠曲测试外，还通过在PeakForce攻丝方式中使用原子力显微镜（AFM）在纳米级确定树脂的弹性模量。因此，可以证明木质素结构域的固有弹性是观察到趋势的主要原因。