Forest Research Center (INIA, CSIC), Ctra. de la Coruña Km 7.5, 28040 Madrid, Spain.
NMR of Facility of Research (SGIker), University of the Basque Country (UPV/EHU), Avenida Tolosa 72, 20018 Donostia-San Sebastián, Spain.
Molecules. 2021 Jun 23;26(13):3819. doi: 10.3390/molecules26133819.
Some agroforestry residues such as orange and olive tree pruning have been extensively evaluated for their valorization due to its high carbohydrates content. However, lignin-enriched residues generated during carbohydrates valorization are normally incinerated to produce energy. In order to find alternative high added-value applications for these lignins, a depth characterization of them is required. In this study, lignins isolated from the black liquors produced during soda/anthraquinone (soda/AQ) pulping of orange and olive tree pruning residues were analyzed by analytical standard methods and Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (solid state C NMR and 2D NMR) and size exclusion chromatography (SEC). Thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and antioxidant capacity (Trolox equivalent antioxidant capacity) were also evaluated. Both lignins showed a high OH phenolic content as consequence of a wide breakdown of β-aryl ether linkages. This extensive degradation yielded lignins with low molecular weights and polydispersity values. Moreover, both lignins exhibited an enrichment of syringyl units together with different native as well as soda/AQ lignin derived units. Based on these chemical properties, orange and olive lignins showed relatively high thermal stability and good antioxidant activities. These results make them potential additives to enhance the thermo-oxidation stability of synthetic polymers.
一些农林废弃物，如橙树和橄榄树修剪枝，由于其高碳水化合物含量，已被广泛评估用于增值利用。然而，在碳水化合物增值过程中产生的富含木质素的残渣通常被焚烧以产生能量。为了为这些木质素寻找替代的高附加值应用，需要对其进行深度特性描述。在这项研究中，通过分析标准方法和傅里叶变换红外光谱（FTIR）、固态 C NMR 和二维 NMR 以及尺寸排阻色谱（SEC）对从橙树和橄榄树修剪枝的苏打/蒽醌（苏打/AQ）浆蒸煮的黑液中分离出的木质素进行了分析。还评估了热分析（热重分析（TGA）、差示扫描量热法（DSC））和抗氧化能力（Trolox 当量抗氧化能力）。两种木质素均表现出高 OH 酚含量，这是由于β-芳基醚键的广泛断裂所致。这种广泛的降解导致木质素具有低分子量和多分散性值。此外，两种木质素都表现出愈创木基单元的富集，以及不同的原生木质素和苏打/AQ 木质素衍生单元。基于这些化学性质，橙树和橄榄树木质素表现出相对较高的热稳定性和良好的抗氧化活性。这些结果使它们成为增强合成聚合物热氧化稳定性的潜在添加剂。
