Dissolution of less-processed wood fibers without bleaching in an ionic liquid: Effect of lignin condensation on wood component dissolution

Impact of Extraction Method on the Structure of Lignin from Ball-Milled Hardwood

Understanding the structure of hardwoods can permit better valorization of lignin by enabling the optimization of green, high-yield extraction protocols that preserve the structure of wood biopolymers. To that end, a mild protocol was applied for the extraction of lignin from ball-milled birch. This made it possible to understand the differences in the extractability of lignin in each extraction step. The fractions were extensively characterized using 1D and 2D nuclear magnetic resonance spectroscopy, size exclusion chromatography, and pyrolysis-gas chromatography-mass spectrometry. This comprehensive characterization highlighted that lignin populations extracted by warm water, alkali, and ionic liquid/ethanol diverged in structural features including subunit composition, interunit linkage content, and the abundance of oxidized moieties. Moreover, ether- and ester-type lignin-carbohydrate complexes were identified in the different extracts. Irrespective of whether natively present in the wood or artificially formed during extraction, these complexes play an important role in the extractability of lignin from ball-milled hardwood. Our results contribute to the further improvement of lignin extraction strategies, for both understanding lignin as present in the lignocellulosic matrix and for dedicated lignin valorization efforts.

Extraction and isolation of lignin from ash tree (Fraxinus exselsior) with protic ionic liquids (PILs)

Protic ionic liquids (PILs) have been considered effective solvents for the selective separation and recovery of cellulose from lignocellulosic biomass. However, PILs can also be utilized for the extraction and conversion of lignin into fuels and value-added products. The objective of this work was to study the extraction of lignin from ash tree (Fraxinus exselsior) hardwood biomass using three different PILs-pyridinium acetate, pyridinium formate [Py][For], and pyrrolidinium acetate. Fiber analysis was used to determine the biochemical composition of the left-over biomass after lignin separation. FTIR and NMR were applied to determine the structure of dissolved lignin. Additionally, the regeneration potential and recyclability of PILs were assessed. Our results demonstrate that treatment with [Py][For] at 75 °C yields the highest percentage of lignin dissolution from biomass. This indicates that PILs could be used for Kraft lignin dissolution as well as separation of lignin from raw, milled biomass.

Trends on the Cellulose-Based Textiles: Raw Materials and Technologies

There is an emerging environmental awareness and social concern regarding the environmental impact of the textile industry, highlighting the growing need for developing green and sustainable approaches throughout this industry's supply chain. Upstream, due to population growth and the rise in consumption of textile fibers, new sustainable raw materials and processes must be found. Cellulose presents unique structural features, being the most important and available renewable resource for textiles. The physical and chemical modification reactions yielding fibers are of high commercial importance today. Recently developed technologies allow the production of filaments with the strongest tensile performance without dissolution or any other harmful and complex chemical processes. Fibers without solvents are thus on the verge of commercialization. In this review, the technologies for the production of cellulose-based textiles, their surface modification and the recent trends on sustainable cellulose sources, such as bacterial nanocellulose, are discussed. The life cycle assessment of several cellulose fiber production methods is also discussed.

Comparison of Two Acid Hydrotropes for Sustainable Fractionation of Birch Wood

This study reports on a comparative study of acid hydrotropic fractionation (AHF) of birch wood using maleic acid (MA) and p-toluenesulfonic acid (p-TsOH). Under the same level of delignification, lignin dissolved by MA is much less condensed with a higher content of ether aryl β-O-4 linkages. Lignin depolymerization dominated in MA hydrotropic fractionation (MAHF) and resulted in a single lower molecular weight peak, in contrast to the competitive depolymerization and repolymerization in p-TsOH AHF with a bimodal distribution. The less condensed MA-dissolved lignin facilitated catalytic conversion to monophenols. Carboxylation of residual lignin in fractionated cellulosic water-insoluble solids (WISs) enhanced enzymatic saccharification by decreasing nonproductive cellulase binding to lignin. At a low cellulase loading of 10 FPU g^-1 glucan, saccharification of WIS-M_T120 from MAHF at 120 °C was 95 % compared with 48 % for WIS-P_T85 from p-TsOH AHF at 85 °C under the same level of delignification of 63 %. Residual lignin carboxylation also facilitated nanofibrillation of WIS for producing lignin-containing cellulose nanofibrils (LCNFs) through an enhanced lignin lubrication effect, which substantially decreases fibrillation energy. LCNFs from only one pass of microfluidization of WIS-M_T120 have the same morphology as those from WIS-P_T85 after three passes. MA also has a lower solubility and higher minimal hydrotropic concentration, which facilitated acid recovery. MA is U.S. Food and Drug Administration (FDA)-approved as an indirect food additive, affording significant advantages compared with p-TsOH for biorefinery applications.