Characterization of Organosolv Birch Lignins: Toward Application-Specific Lignin Production

Organosolv pretreatment represents one of the most promising biomass valorization strategies for renewable carbonbased products; meanwhile, there is an overall lack of holistic approach to how extraction conditions affect the suitable end-usages. In this context, lignin extracted from silver birch (Betula pendula L.) by a novel hybrid organosolv/steam-explosion treatment at varying process conditions (EtOH %; time; catalyst %) was analyzed by quantitative NMR (H-1-C-13 HSQC; C-13 NMR; P-31 NMR), gel permeation chromatography, Fourier transform infrared (FT-IR), Pyr-gas chromatography-mass spectroscopy (GC/MS), and thermogravimetric analysis, and the physicochemical characteristics of the lignins were discussed regarding their potential usages. Characteristic lignin interunit bonding motifs, such as beta-O-4', beta-beta', and beta-5', were found to dominate in the extracted lignins, with their abundance varying with treatment conditions. Low-molecular-weight lignins with fairly unaltered characteristics were generated via extraction with the highest ethanol content potentially suitable for subsequent production of free phenolics. Furthermore, beta-5' and beta-5' structures were predominant at higher acid catalyst contents and prolonged treatment times. Higher acid catalyst content led to oxidation and ethoxylation of side-chains, with the concomitant gradual disappearance of p-hydroxycinnamyl alcohol and cinnamaldehyde. This said, the increasing application of acid generated a broad set of lignin characteristics with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation purposes.

Automated summary

The extraction of lignin from silver birch under varying process conditions results in lignins with characteristic bonding motifs. High ethanol content extraction generates low molecular weight lignins suitable for producing free phenolics, while higher acid catalyst content leads to oxidation of side chains and the potential production of lignins with various applications. Increasing the acid catalyst content generates lignin with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation.