Short-time deep eutectic solvents pretreatment enhanced production of fermentable sugars and tailored lignin nanoparticles from abaca

Improved antioxidant activity of pretreated lignin nanoparticles: Evaluation and self-assembly

Lignin nanoparticles (LNPs) have gained significant attention for their potential as natural antioxidants. This study investigated the effect of various pretreatment methods on the lignin structure and subsequent antioxidant activity of LNPs. Among four pretreated LNPs, hydrothermal LNPs exhibited the highest antioxidant activity, surpassing unpretreated, acid-pretreated and kraft LNPs, with an impressive efficacy of 91.6%. The relationship between LNPs' structure and antioxidant activity was revealed by 2D heteronuclear singular quantum correlation (1H13C HSQC) and 31P nuclear magnetic resonance (NMR). 1H13C HSQC suggested the cleavage of β-O-4 ether bonds, as well as a decrease in ferulic acid and p-coumaric acid, which directly influenced the antioxidant activity of LNPs. 31P NMR demonstrated a positive correlation between the total hydroxyl group content and the antioxidant activity. Besides, an isothermal kinetic model for scavenging free radicals was established based on Langmuir kinetic model instead of Freundlich model. Moreover, multilayer LNPs, based on layer-by-layer self-assembly, were prepared and exhibited remarkable antioxidant activity of 95.8%. More importantly, when blended with pure cosmetic cream, the multilayer LNPs maintained antioxidant activity of 86.7%. These finding may promote the practical applications of biomolecules, e.g. lignin additives in cosmetics and pharmaceuticals.

Role of lignin in synergistic digestibility improvement of wheat straw by novel alkaline deep eutectic solvent and tetrahydrofuran pretreatment

A novel efficient pretreatment system containing alkaline deep eutectic solvent (DES) and tetrahydrofuran (THF) was developed in the present study. Under pretreatment conditions of 160 ℃ and 1 h, DES-THF pretreatment was more efficient (81.61%) in cellulose digestibility improvement than DES (choline chloride/monoethanolamine, 67.54%). To further explore lignin structural transformation and lignin-cellulase interaction after pretreatment, milled wood lignin (MWL) was extracted and characterized. Compared with DES-MWL, DES-THF-MWL showed an increased carboxyl group content (24.0%) and decreased condensed phenolic hydroxyl content (9.1%). In DES-MWL, β-O-4 content was 21.79%, while in DES-THF-MWL, β-O-4 accounted for 45.45%, indicating that the addition of THF alleviated cleavage of β-O-4 alkyl ether bonds. Fluorescence emission spectroscopy results showed that quenching mechanism of DES-THF-MWL and cellulase was dynamic, which was different from other lignin. Compared with DES-MWL, decreased Ka between DES-THF-MWL and cellulase indicated decreasing interaction between them. DES-THF pretreatment provides a novel pretreatment method for bioenergy.

Integrated acetic acid and deep eutectic solvent pretreatment on poplar for co-production of xylo-oligosaccharides, fermentable sugars and lignin antioxidants/adsorbents

Efficient fractionation of lignocellulosic biomass in usable forms of hemicellulose, cellulose and lignin is very important for the sustainable lignocellulosic biorefinery. Herein, poplar sawdust was pretreated with an integrated process composed of acetic acid pre-hydrolysis (170 °C, 60 min) for xylo-oligosaccharides (XOS) production and mild deep eutectic solvent (90-130 °C, 60 min) post-delignification for recovering lignin fractions, resulting in easily hydrolyzed cellulose fraction. Results showed that, after integrated pretreatment and enzymatic hydrolysis, 51 % of xylan and 92 % of glucan in raw biomass could be converted to XOS (DP 2-6) and glucose, respectively, while 71 % of the original lignin could be recovered in DES solvent. The resulting XOS were proven to ensure the growth of probiotics, Bifidobacterium adolescentis. Besides, the lignin macromolecules recovered from DES solvent showed high-purity (around 95 %), low-molecular weight (Mw around 2000), small particle size (270-170 nm) and high-PhOH (3.08 mmol/g) content, which were likely relevant to the excellent antioxidant activity (RSI = 15.16) and adsorbent activity (Pb(II) 461.89 mg/g lignin). Finally, mass balance and energy analysis revealed that the integrated pretreatment could be used as a promising approach for the production of bio-based chemicals and materials from woody biomass.

Structural elucidation and targeted valorization of untractable lignin from pre-hydrolysis liquor of xylose production via a simple and robust separation approach

Effective separation of lignin macromolecules from the xylose pre-hydrolysates (XPH) during the xylose production, thus optimizing the separation and purification process of xylose, is of great significance for reducing the production costs, achieving the high value-added utilization of lignin and increasing the industrial revenue. In this study, a simple and robust method (pH adjustment) for the separation of lignin from XPH was proposed and systematically compared with the conventional acid-promoted lignin precipitation method. The results showed that the lignin removal ratio (up to 60.34 %) of this simple method was higher than that of the conventional method, and the proposed method eliminated the necessity of heating and specialized equipment, which greatly reduced the separation cost. Meanwhile, this simple method does not destroy the components in XPH (especially xylose), ensuring the yield of the target product. On the other hand, the obtained lignin was nano-scale with less condensed structures, which also possessed small molecular weights with narrow distribution, excellent antioxidant activity (8-14 times higher than commercial antioxidants) and UV protection properties. In conclusion, the proposed simple separation method could effectively separate lignin from XPH at low cost, and the obtained lignin had potential commercial applications, which would further enhance the overall profitability of industrial production.

A novel mineral-acid free biphasic deep eutectic solvent/γ-valerolactone system for furfural production and boosting the enzymatic hydrolysis of lignocellulosic biomass

The failure of hemicellulose valorization in a deep eutectic solvent (DES) pretreatment has become a bottleneck that challenges its further development. To address this issue, this study developed a DES/GVL (γ-valerolactone) biphasic system for effective hemicellulose-furfural conversion, enhanced cellulose saccharification and lignin isolation. The results indicated that the biphasic system could significantly improve the lignin removal (as high as 89.1%), 86.0% higher than the monophasic DES, accompanied by ∼100% hemicellulose degradation. Notably, the GVL in the biphasic solvent restricted the condensation of hemicellulose degradation products, which as a result generated large amount of furfural in the pretreatment liquid with a yield of 68.6%. With the removal of hemicellulose and lignin, cellulose enzymatic hydrolysis yield was boosted and reached near 100%. This study highlighted that the novel DES/GVL is capable of fractionating the biomass and benefiting their individual utilization, which could provide a new biorefinery configuration for a DES pretreatment.

Natural arginine-based deep eutectic solvents for rapid microwave-assisted pretreatment on crystalline bamboo cellulose with boosting enzymatic conversion performance

Development of amino acid-based natural deep eutectic solvents (DESs) pretreatment technology on lignocellulosic biomass is a promising approach to biorefinery. In this study, for arginine-based DESs with different molar ratios, the viscosity and Kamlet-Taft solvation parameters were quantified to evaluate the pretreatment performance on bamboo biomass. Further, microwave assisted DES pretreatment was eminent, evidenced by 84.8% lignin removal and increased saccharification yield (from 6.3% to 81.9%) in moso bamboo at 120 °C and ratio of 1:7 (arginine: lactic acid). Results showed degradation of lignin molecules together with release of phenolic hydroxyl units after DESs pretreatment, which is conducive to subsequent utilization. Meanwhile, DES-pretreated cellulose exhibited unique structural characteristics including destroyed crystalline region of cellulose (Crystallinity Index from 67.2% to 53.0%), decreased crystallite size (from 3.41 nm to 3.14 nm) and roughened fiber surface. Thus, arginine-based DES pretreatment has excellent potential in bamboo lignocellulose pretreatment.

Improved enzymatic saccharification of bulrush via an efficient combination pretreatment

Glycerol (Gly) was selected as hydrogen-bond-donor for preparing ChCl-based DES (ChCl:Gly), and the mixture of ChCl:Gly (20 wt%) and NaOH (4 wt%) was utilized for combination pretreatment of bulrush at 100 °C for 60 min (severity factor LogRo = 1.78). The effects of DES pretreatment on the chemical composition, microstructure, crystal structure, and cellulase hydrolysis were explored. NaOH-ChCl:Gly could remove lignin (80.1%) and xylan (66.8%), and the enzymatic digestibility of cellulose reached 87.9%. The accessibility of bulrush was apparently increased to 645.2 mg/g after NaOH-ChCl:Gly pretreatment. The hydrophobicity and lignin surface area were reduced to 1.56 L/g and 417 m2/g, respectively. The crystallinity of cellulose was increased from 20.8% to 55.6%, and great changes in surface morphology were observed, which explained the improvement of enzymatic hydrolysis efficiency. Overall, DES combined with alkali treatment could effectively promote the removal of lignin and xylan in bulrush, thus the relative saccharification activity was greatly affected.

Preparation of water-insoluble lignin nanoparticles by deep eutectic solvent and its application as a versatile and biocompatible support for the immobilization of α-amylase

As one of the most abundant biopolymers, lignin is a widely available resource. However, its potential largely remains untapped, with most of it ending up as waste from industries like paper production, pulp processing, and bio-refining. The research undertaken in this study focused on the extraction of lignin from agroforestry waste using a deep eutectic solvent (DES) as a carrier for α-amylase immobilization, resulting in high stability and reusability. Several techniques, including Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and the Brunauer-Emmett-Teller (BET) method were employed to examine the structure and morphology of both the extracted lignin and the immobilized enzyme. The temperature used to recover lignin by DES would affect immobilization efficiency and enzyme loading by influencing its specific surface area, pore size, and volume distribution. Investigations using Nuclear Overhauser Effect Spectroscopy (NOESY) uncovered that the hydroxyl groups in G, H, and S units and the β-O-4 structure of lignin primarily serve as binding sites for enzyme molecules. Immobilized α-amylase demonstrated a higher pH and thermal stability level, with an optimal pH of 7.0 and temperature of 100 °C, compared to the free enzyme, which exhibited optimal activity at a pH of 6.5 and temperature of 90 °C. Importantly, immobilized α-amylase retained >80 % of its initial activity even after 28 days at room temperature, and it maintained 70 % of its activity after being reused 12 times. These findings strongly suggest that lignin derived from agroforestry residues holds promising potential as a future versatile immobilization material, a prospect integral to society's sustainable development.

CD44 mediated colon cancer targeting mutlifaceted lignin nanoparticles: Synthesis, in vitro characterization and in vivo efficacy studies

Hyaluronic acid (HA) coated irinotecan loaded lignin nanoparticles (HDLNPs) were synthesized using ionic interaction method. Optimized nanoparticles were characterized for their active chemotherapeutic targeting potential to CD44 receptors overly-expressed on cancer cells. Blood component interaction studies supported hemocompatible nature of HDLNPs and also demonstrated their sustained plasma residence property. Cell anti-proliferation and mitochondrial depolarization studies on HT-29 cells suggest significantly (p < 0.01) improved chemotherapeutic efficacy of HDLNPs. In vitro cell based studies showed that nanoparticles have retained antioxidant activity of lignin that can prevent cancer relapse. In vivo biodistribution studies in tumor-bearing Balb/c mice confirmed improved drug localization in tumor site for longer duration. Tumor regression and histopathological studies indicated the efficacy ofligand-assisted targeting chemotherapy over the conventional therapy. Hematological and biochemical estimation suggested that irinotecan-associated myelosuppression, liver steatosis and rare kidney failure can be avoided by its encapsulation in HA-coated lignin nanoparticles. HDLNPs were found to be stable over a period of 12 months.

Physicochemical characterization and antioxidant activity of polysaccharides from Chlorella sp. by microwave-assisted enzymatic extraction

Microwave-assisted enzymatic extraction (MAEE) was used for the separation of polysaccharides from micro-Chlorella. The extraction condition of MAEE was optimized by Box-Behnken design and response surface methodology. Results showed that the optimal condition for the extraction of Chlorella sp. crude polysaccharides (CSCP) was at 50°C for 2.3 h with 380 W of microwave power and 0.31% of enzyme dosage. Under the optimal extraction condition, the extraction yield of CSCP reached 0.72%. Similarly, the α-amylase modification conditions of the CSCP were also optimized, in which the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate was used as the response value. The scavenging rate of DPPH free radicals was 17.58% when enzyme dosage was 271 U/g at 51°C for 14 min. Moreover, the enzyme-modified CSCP presented a typical heteropolysaccharide mainly including glucose (48.84%), ribose (13.57%) and mannose (11.30%). MAEE used in this work achieved a high extraction yield of CSCP, which provides an efficient method for the extraction of CSCP from Chlorella sp.

A continuous flow mode with a scalable tubular reactor for the green preparation of stable alkali lignin nanoparticles assisted by ultrasound

Lignin nanoparticles (LNPs) have become a hot topic recently because of their improved physicochemical properties and the excellent integration into various industrial sectors compared to lignin. However, the green large-scale production of stable LNPs severely restricts the high-value applications of LNPs. In this work, a simple and potentially scalable continuous-flow mode setup with a tubular flow reactor was designed for the green preparation of stable alkali LNPs assisted by ultrasound. When the flow rates of lignin solution and nitric acid solution were 8.00 mL/min and 2.67 mL/min respectively, and the length of the tube was 5.5 m, the average residence time of mixed solution was 62.2 s in the tubular reactor. Spheroid nanoparticles with an average size of 97.2 nm were obtained under this optimized condition. Furthermore, the results showed a better control of the mixing compared to the batch process, resulting in a homogeneous distribution of smaller particle sizes thus improving stability and UV-blocking properties. This is attributed to the better mixing and excellent mass transfer characteristics in the tube, which provides favorable conditions for the full contact and uniform dispersion of the mixed solution. More importantly, continuous flow mode makes it possible to prepare LNPs with excellent physicochemical properties on a large scale, which will bring great opportunities for the industrial production and application of LNPs.

Acidic deep eutectic solvent assisted mechanochemical delignification of lignocellulosic biomass at room temperature

Lignocellulosic biomass is the most abundant natural polymer on Earth, but the efficient fractionation and refinery of all its components remain challenging. Acidic deep eutectic solvents refining is a promising method, while it is likely to cause lignin condensation and carbohydrates degradation, especially at server operation conditions. Here we propose the use of acidic deep eutectic solvent (DES), choline chloride/p-toluenesulfonic acid assisted mechanochemical pretreatment (DM) for efficient lignocellulose fractionation at mild condition. Four representative lignocellulose, wheat straw, moso bamboo, poplar wood and pine wood were selected at varied milling time (3, 6 h) to assess the fractionation ability of this strategy. This DM pretreatment demonstrated a rather high cellulose retentions (∼90 %) and extent of delignification for wheat straw and bamboo biomass, which corresponds to a high extent of enzymatic hydrolysis (∼75.5 %) for sugar platform pursuing. The extracted lignin showed rather high content of β-O-4' leakages due to the swelling effect of deep eutectic solvent and mild operation conditions. This work provided a promising strategy to fractionate lignocellulose using deep eutectic solvents with the goal of simultaneous cellulose hydrolysis and reactive lignin obtaining that is usually difficult to realize using traditional chemical fractionation approach.

Comparative study of acid- and alkali-catalyzed 1,4-butanediol pretreatment for co-production of fermentable sugars and value-added lignin compounds

BACKGROUND

Organosolv pretreatment is one of the most efficient methods for delignification and boosting biomass saccharification. As compared to typical ethanol organosolv pretreatments, 1,4-butanediol (BDO) organosolv pretreatment is a high-boiling-point solvent pretreatment, which can generate low pressure in the reactor during high temperature cooking that improves the operation safety. Although several studies showed that organosolv pretreatment can lead to effective delignification and enhancement in glucan hydrolysis, there has been no studies on acid- and alkali-catalyzed BDO pretreatment, as well as their comparison on promoting biomass saccharification and lignin utilization.

RESULTS

It was shown that BDO organosolv pretreatment was more effective in removing lignin from poplar as compared with typical ethanol organosolv pretreatment under the same pretreatment conditions. HCl-BDO pretreatment with 40 mM acid loading led to 82.04% of original lignin removed from biomass, as compared to the lignin removal of 59.66% in HCl-Ethanol pretreatment. Besides, acid-catalyzed BDO pretreatment was more effective in improving the enzymatic digestibility of poplar than alkali-catalyzed BDO pretreatment. As a result, HCl-BDO with acid loading of 40 mM provided a good enzymatic digestibility of cellulose (91.16%) and the maximum sugar yield of 79.41% from original woody biomass. The linear correlations between physicochemical structure (e.g., fiber swelling, cellulose crystallinity, crystallite size, surface lignin coverage and cellulose accessibility) changes of BDO pretreated poplar and enzymatic hydrolysis were plotted to figure out the main factors that influenced biomass saccharification. Moreover, acid-catalyzed BDO pretreatment mainly brought about the phenolic hydroxyl (PhOH) groups formation in lignin structure, while alkali-catalyzed BDO pretreatment mostly led to the lower molecular weight of lignin.

CONCLUSIONS

Results indicated that the acid-catalyzed BDO organosolv pretreatment could significantly improve enzymatic digestibility of the highly recalcitrant woody biomass. The great enzymatic hydrolysis of glucan resulted from increased cellulose accessibility, which mostly associated with the higher degree of delignification and hemicellulose solubilization, as well as the more increase in fiber swelling. Besides, lignin was recovered from the organic solvent, which could be used as natural antioxidants. The formation of phenolic hydroxyl groups in lignin structure and the lower molecular weight of lignin contributed to its greater radical scavenging capacity.

Green and sustainable extraction of lignin by deep eutectic solvent, its antioxidant activity, and applications in the food industry

Lignin, an amorphous biomacromolecule abundantly distributed in the plant kingdom, has gained considerable attention due to its intrinsic bioactivities and renewable nature. Owing to its polyphenolic structure, lignin has a variety of human health activities, including antioxidant, antimicrobial, antidiabetic, antitumor, and other activities. The extraction of lignin from various sources in a green and sustainable manner is critical in the food industry. Deep eutectic solvent (DES) has recently been recognized as a class of safe and environmentally friendly media capable of efficiently extracting lignin. This article comprehensively reviews the recent advances in lignin extraction using DES, discusses the influential factors on the antioxidant activity of lignin, interprets the relationship between antioxidant activity and lignin structure, and overviews the applications of lignin in the food industry. We aim to highlight the advantages of DES in lignin extraction and valorization from the nutrition and food views.

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl₃·6H₂O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl₃·6H₂O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55-1.73) and molecular weight (1380-2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

Nanogrinding/ethanol activation facilitating lignin fractionation for preparation of monodispersed lignin nanoparticles

Lignin nanoparticles (LNPs), as one of green and sustainable biological macromolecules, have attracted great attention owing to their promising potentials in many valorized fields. However, the lignin heterogeneity seriously restricts the controllable preparation of LNPs. Herein, a facile nanogrinding activation combining anhydrous ethanol dissolution process was developed to efficiently homogenize lignin prior to gradient ethanol fractionation. Two lignin fractions were obtained from nanogrinding activation/ethanol dissolution followed by gradient ethanol fractionation: L-fractions and S-fractions. Therefore, monodispersed LNPs with unique concave hollow nanostructure and large particle size, and monodispersed LNPs with solid core nanostructure and small particle size were successfully prepared from L-fractions and S-fractions, respectively, via a GVL/water anti-solvent method. The proposed LNPs formation mechanisms facilitated by nanogrinding activation/ethanol dissolution treatment were demonstrated. This study put forwards a facile and green integrated approach for monodispersed LNPs preparation with controllable morphology and particle size.

Mechanism study of ternary deep eutectic solvents with protonic acid for lignin fractionation

This paper investigated the fractionation of lignin by ternary DES of different polyols using simulation calculation. ChCl-EG-PTSA showed the highest degradability of lignin with the absolute value of total interaction energy of -8023.80 kJ/mol, and the total number of hydrogen bonds was 91.4. The highest degradability was observed for ChCl:EG: PTSA = 2:4:1. The results show that CL^- plays a dominant role in lignin fractionation and readily forms hydrogen bonds with γ-OH. The difference is that the polyol preferred to form hydrogen bonds with α-OH in lignin. The addition of PTSA provided protons to the original system. It formed a new π-π stacking interaction with the lignin benzene ring, which destroyed the π-π stacking interaction between the original lignin. And increased the interaction of DES on lignin from -39.73 kcal/mol to -58.15 kcal/mol based on DFT.

Valorization of bamboo shoot shell waste for the coproduction of fermentable sugars and xylooligosaccharides

In this work, hydrothermal pretreatment (autohydrolysis) was coupled with endo-xylanase enzymatic hydrolysis for bamboo shoot shell (BSS) to produce glucose and valuable xylooligosaccharides (XOS) rich in xylobiose (X2) and xylotriose (X3). Results showed that the enzymatic hydrolysis efficiency of pretreated BSS residue reached 88.4% with addition of PEG during the hydrolysis process. To enrich the portions of X2–X3 in XOS, endo-xylanase was used to hydrolyze the XOS in the prehydrolysate, which was obtained at the optimum condition (170°C, 50 min). After enzymatic hydrolysis, the yield of XOS reached 25.6%, which contained 76.7% of X2–X3. Moreover, the prehydrolysate contained a low concentration of fermentation inhibitors (formic acid 0.7 g/L, acetic acid 2.6 g/L, furfural 0.7 g/L). Based on mass balance, 32.1 g of glucose and 6.6 g of XOS (containing 5.1 g of X2-X3) could be produced from 100.0 g of BSS by the coupled technology. These results indicate that BSS could be an economical feedstock for the production of glucose and XOS.

Valorization of hydrolysis lignin from a spruce-based biorefinery by applying γ-valerolactone treatment

Hydrolysis lignin, i.e., the hydrolysis residue of cellulosic ethanol plants, was extracted with the green solvent γ-valerolactone (GVL). Treatments at 170-210 °C were performed with either non-acidified GVL/water mixtures (NA-GVL) or with mixtures containing sulfuric acid (SA-GVL). SA-GVL treatment at 210 °C resulted in the highest lignin solubilization (64% (w/w) of initial content), and 76% of the solubilized mass was regenerated by water-induced precipitation. Regenerated lignins were characterized through compositional analysis with sulfuric acid, as well as using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), high-performance size-exclusion chromatography (HPSEC), solid-state cross-polarization/magic angle spinning ¹³C nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy, ¹H-¹³C heteronuclear single-quantum coherence NMR (HSQC NMR), and Fourier-transform infrared (FTIR) spectroscopy. The characterization revealed that the main difference between regenerated lignins was their molecular weight. Molecular weight averages increased with treatment temperature, and they were higher and had broader distribution for SA-GVL lignins than for NA-GVL lignins.

Comparative investigation of the structural characteristics of tobacco stalk lignin during the DES and alkaline deconstruction toward sustainable materials

Lignin polymer as a natural aromatic macromolecule presents significant prospects in producing functional and sustainable materials, and achieving a comprehensive characterization will facilitate their target valorization. In the present study, deep eutectic solvent (DES) and alkaline delignification were adopted to deconstruct tobacco stalk before and after hydrothermal pretreatment, obtaining diverse lignin fractions with fascinating characteristics. DES lignin exhibited a higher yield and homogenous molecular structure than MWL. A severe cleavage of the inter-unit linkages in lignin was also observed. This result mostly originated from the efficient delignification of the DES deconstruction system adopted. Moreover, all the recovered lignin fractions exhibited good micro-nanoparticle size that can enhance the valorization of lignin in nanomaterial production, in which the hydrothermal-assisted DES deconstruction promoted the formation of the smaller lignin nanoparticle size. Next, all the recovered lignin presented an excellent UV absorption and structure-related absorption performance or thermal properties. Overall, this work provides an important foundation for further exploiting DES/alkaline delignification lignin that can be applied as an ideal feedstock for producing sustainable functional or micro/nanomaterials.

Green and Efficient Preparation of Tailed Lignin Nanoparticles and UV Shielding Composite Films

Lignin nanoparticles (LNP) with various morphologies could be prepared with solvent-antisolvent methods. However, the employed toxic chemicals limited its large-scale application. In this study, an extremely green method using only ethanol and water as solvent and antisolvent was reported. Besides, with the syringaldehyde (SA) addition and its anchoring action on the lignin particles, a forming process of the tailed structure was observed and resulted. Moreover, the improved electronegativity originating from the phenolic hydroxyl groups enhanced the size distribution uniformity, and the new absorption peaks at 1190 cm^-1 demonstrated the involvement of SA in the LNP formation. Lastly, the tailed lignin nanoparticles (T-LNP) composited with, respectively, polyvinyl alcohol, chitosan, cellulose nanofibers, cationic etherified starch, and sodium alginate were successfully prepared. The outstanding UV-shielding and free radical scavenging properties in the above composites showed their great potential in wide applications in packaging materials.

Structural elucidation and targeted valorization of poplar lignin from the synergistic hydrothermal-deep eutectic solvent pretreatment

Elucidating the structural variations of lignin during the pretreatment is very important for lignin valorization. Herein, poplar wood was pretreated with an integrated process, which was composed of AlCl₃-catalyzed hydrothermal pretreatment (HTP, 130-150 °C, 1.0 h) and mild deep-eutectic solvents (DES, 100 °C, 10 min) delignification for recycling lignin fractions. Confocal Raman Microscopy (CRM) was developed to visually monitor the delignification process during the HTP-DES pretreatment. NMR characterizations (2D-HSQC and ³¹P NMR) and elemental analysis demonstrated that the lignin fractions had undergone the following structural changes, such as dehydration, depolymerization, condensation. Molecular weights (GPC), microstructure (SEM and TEM), and antioxidant activity (DPPH analysis) of the lignins revealed that the DES delignification resulted in homogeneous lignin fragments (1.32 < PDI < 1.58) and facilitated the rapid assemblage of lignin nanoparticles (LNPs) with controllable nanoscale sizes (30-210 nm) and excellent antioxidant activity. These findings will enhance the understanding of structural transformations of the lignin during the integrated process and maximize the lignin valorization in a current biorefinery process.

Efficient fractionation of bamboo residue by autohydrolysis and deep eutectic solvents pretreatment

Bamboo processing residue, which is rich in parenchyma cells, was treated as huge waste in bamboo processing industry, such as reassemble bamboo and bamboo flooring. Herein, autohydrolysis and rapid different deep eutectic solvents (DES) delignification strategy were consecutively performed to remove hemicelluloses and lignin from bamboo processing residue. The xylooligosaccharides (XOS) with high yield (34.35%) was achieved in the autohydrolysis process. Results showed that alkaline DES pretreatment resulted in the highest glucose yield (88.22%) and relatively high delignification rate (83.75%) as well as well-preserved lignin structures. However, the lignin fractions obtained under acidic DES conditions were tending to assemble into lignin nanoparticles (LNPs) and having excellent antioxidant activity as compared to those obtained from alkaline DES system. In brief, the combination of autohydrolysis and rapid DES delignification can achieve orientated fractionation of the components from the industrialized bamboo.

Ultrafast alkaline deep eutectic solvent pretreatment for enhancing enzymatic saccharification and lignin fractionation from industrial xylose residue

An aspirational pretreatment method for efficient fractionation and tailored valorization of large industrial biomass can ensure the realizability of sustainable biorefinery strategies. In this study, an ultrafast alkaline deep eutectic solvents (DES) pretreatment strategy was developed to efficiently extract the lignin nanoparticles and retain cellulose residues that could be readily enzymatic saccharified to obtain fermentative glucose for the bioenergy production from industrial xylose residue. Results showed that the DES pretreatment had excellent delignification performance and the regenerated DES lignin nanoparticles exhibited well-preserved structures and excellent antioxidant activity, as well as low molecular weights and relatively uniform size distribution, which could facilitate downstream catalytic degradation for production of chemicals and preparation of lignin-based materials. Under the optimal condition (DES pretreatment: 80 °C, 10 min; saccharification: 10 FPU/g, 5 wt%, 100 mg/g Tween 80), the glucose yield of 90.12% could be achieved, which was dramatically increased compared to raw materials.

Isolation and Fractionation of the Tobacco Stalk Lignin for Customized Value-Added Utilization

The value-added utilization of tobacco stalk lignin is the key to the development of tobacco stalk resources. However, the serious heterogeneity is the bottleneck for making full use of tobacco stalk lignin. Based on this, lignin was separated from tobacco stalk through hydrothermal assisted dilute alkali pretreatment. Subsequently, the tobacco stalk alkaline lignin was fractionated into five uniform lignin components by sequential solvent fractionation. Advanced spectral technologies (FT-IR, NMR, and GPC) were used to reveal the effects of hydrothermal assisted dilute alkali pretreatment and solvent fractionation on the structural features of tobacco stalk lignin. The lignin fractions extracted with n-butanol and ethanol had low molecular weight and high phenolic hydroxyl content, thus exhibiting superior chemical reactivity and antioxidant capacity. By contrast, the lignin fraction extracted with dioxane had high molecular weight and low reactivity, nevertheless, the high residual carbon rate made it suitable as a precursor for preparing carbon materials. In general, hydrothermal assisted dilute alkali pretreatment was proved to be an efficient method to separate lignin from tobacco stalk, and the application of sequential solvent fractionation to prepare lignin fractions with homogeneous structural features has specific application prospect.