Structural characterizations of lignins extracted under same severity using different acids

• Published in: International journal of biological macromolecules 2022-01, Vol.194, p.204-212
• Main Authors: Shakeel, Usama, Li, Xinlong, Wang, Biao, Geng, Fanhui, Rehman, Muhammad Saif Ur, Zhang, Kai, Xu, Jian
• Format: Article
• Language: English
• Subjects: Acids - chemistry; Chemical Fractionation - methods; Chemical structural features. 2D-NMR (HSQC); Lignin - chemistry; Lignin - isolation & purification; Lignin applications; Lignin valorization; Mild acidolysis lignin (MAL); Molecular Structure; Molecular Weight; Spectrum Analysis; Tailor-made lignin
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2021.11.171

As the vital renewable feedstock originated from carbon-neutral resources, due to prominent aromaticity lignin owns the potential to produce high value-added products. Multi-functional lignin valorization demands efficient lignin extraction at milder conditions to keep its structure intact to substitute petroleum-based reactants. Lignin extraction severity (LES) is considered as the primary factor affecting the structure of extracted lignin and ultimately determines its applications. Except for the LES, the selection of suitable reagents for lignin extraction concerned with specific applications is crucially important. To explore the influence of different reagents, this study focused on lignin extraction employing the commonly used strong acids at the same LES. Four lignin preparations were extracted using 80% aqueous dioxane with the addition of H2O (L1), HCl, H2SO4 and HNO3 (pH = 1.30 ± 0.01 L2, L3 and L4, respectively). Analytical high-sensitive NMR (31P and 2D-HSQC) together with other characterizations (FTIR and GPC) were successfully employed and quantified while unveiling the structural heterogeneity among extracted lignin preparations. At the same LES, different reagents yielded lignin with varying structural characteristics and were potentially suitable for different applications. •Selection of suitable reagents was important for tailor-made lignin extraction towards its application.•Synergistic effect of H+ ions and anions caused lignin structure alteration.•The same severity factor with different reagents yielded lignin with different structural characterizations for different applications.•Quantification revealed the structural heterogeneity among extracted lignin preparation.