Wang Yun-Yan, Meng Xianzhi, Pu Yunqiao, Ragauskas Arthur J
Center for Renewable Carbon, Department of Forestry, Wildlife and Fisheries, University of Tennessee Institute of Agriculture, Knoxville, TN 37996, USA.
Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996, USA.
Polymers (Basel). 2020 Oct 3;12(10):2277. doi: 10.3390/polym12102277.
The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.
在过去几十年里，人们一直在不断探索将木质素转化为高价值产品的方法。天然状态下，木质素是一组由苯丙烷类化合物组成的多相聚合物。主要的商业木质素流，包括硫酸盐木质素、木质素磺酸盐、苏打木质素和有机溶剂木质素，是通过包括造纸和制浆工业以及新兴的木质纤维素生物精炼厂在内的工业过程生产的。尽管木质素被视为一种低成本的可再生原料，可替代石油基材料，但其在聚合物材料中的应用却因木质素的低反应性和固有的物理化学性质而受到抑制。因此，人们开发了各种木质素改性策略来克服这些问题。在此，我们综述了功能化木质素在商品聚合物中的应用进展，这些聚合物包括热固性树脂、共混物/复合材料、接枝功能化共聚物和碳纤维前驱体。在聚氨酯、酚醛和环氧树脂等热固性树脂的合成中，它们被共价结合到聚合物基体中，讨论的重点是改善工业木质素反应性的化学改性。在共混物/复合材料中，工业木质素的功能化基于调节聚合物组分之间的分子间作用力。此外，接枝功能聚合物已将木质素基共聚物的应用扩展到生物医学材料和增值添加剂领域。不同的改性方法也被应用于促进木质素作为碳纤维前驱体、重金属吸附剂和纳米颗粒的应用。这些新兴领域将为将木质素增值成本效益高地整合到木质纤维素生物精炼厂中创造新的机会。
