Department of Food and Nutrition, University of Helsinki, P.O. Box 66, (Agnes Sjöbergin Katu 2), Helsinki FI-00014, Finland.
Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland.
J Agric Food Chem. 2021 Jun 2;69(21):5955-5965. doi: 10.1021/acs.jafc.1c00705. Epub 2021 May 18.
The complex chemical structure and the fact that many areas in pulping and lignin chemistry still remain unresolved are challenges associated with exploiting lignin. In this study, we address questions regarding the formation and chemical nature of the insoluble residual lignin, the presence of fatty acids in kraft lignin, and the origin of secoisolariciresinol structures. A mild thermal treatment of lignin at maximum kraft-cooking temperatures (∼170 °C) with tall oil fatty acids (TOFA) or in an inert solvent (decane) produced highly insoluble products. However, acetylation of these samples enabled detailed chemical characterization by nuclear magnetic resonance (NMR) spectroscopy. The results show that the secoisolariciresinol (β-β) structure in kraft lignin is formed by rearrangement of the β-aryl ether structure. Furthermore, fatty acids bind covalently to kraft lignin by reacting with the stilbene structures present. It is highly probable that these reactions also occur during kraft pulping, and this phenomenon has an impact on controlling the present kraft pulping process along with the development of new products from kraft lignin.
木质素结构复杂，制浆和木质素化学领域的许多问题仍未得到解决，这些都是在木质素开发过程中面临的挑战。在这项研究中，我们探讨了不溶性残余木质素的形成和化学性质、硫酸盐木质素中脂肪酸的存在以及落叶松脂素结构的起源等问题。在最高制浆温度（约 170°C）下，用妥尔油脂肪酸（TOFA）或惰性溶剂（癸烷）对木质素进行温和的热处理，会产生高度不溶性产物。然而，这些样品的乙酰化可以通过核磁共振（NMR）光谱进行详细的化学表征。结果表明，硫酸盐木质素中的落叶松脂素（β-β）结构是通过β-芳基醚结构的重排形成的。此外，脂肪酸通过与存在的亚苄基结构反应与硫酸盐木质素发生共价结合。在硫酸盐制浆过程中很可能也会发生这些反应，这种现象不仅会影响到控制目前的硫酸盐制浆过程，还会影响到从硫酸盐木质素中开发新产品。
