Facile production of cellulose nanofibers from raw elephant grass by an aluminum chloride-enhanced acidic deep eutectic solvent

Co-production of easily hydrolysable cellulosic substrates and UV-blocking lignin nanoparticles through "lignin-first" polyethylene glycol fractionation

A novel polyethylene glycol (PEG 400)-assisted lignin-first strategy was developed to selectively fractionate sugarcane bagasse while co-producing hydrolyzable cellulosic substrates and structurally modified lignin nanoparticles (LNPs). Under mild conditions catalyzed by Lewis acid (120 °C and 1.5 % AlCl3), the process achieved 92 % cellulose retention, 81 % delignification, and 76 % hemicellulose removal, significantly enhancing hydrolysis efficiency to 86 %. PEG had extensive esterification or etherification modifications on the lignin aromatic monomers, as well as on its Ca position, side-chain aliphatic -OH, and phenolic -OH. PEG-modified lignin retained high β-O-4 linkages, limited recondensation, and improved hydrophilicity, enabling the LNPs preparation with uniform and small particle sizes. Structural analyses revealed that lignin S/G ratio, β-O-4 linkages, molecular weight, and contact angle (R2 > 0.84) strongly influenced the self-assembly of LNPs. The application of LNPs has been broadened in UV-blocking materials, particularly for protecting against ultraviolet A wavelengths (320-400 nm). They demonstrated good biocompatibility, with 94 %-99 % cell viability, alongside enhanced antioxidant activities (1.25-7.6 times higher) and photostability. Adding 1 %-7 % of LNPs elevated the sun protection factor of commercial sunscreen (∼46) to an impressive range of 91.6-143.5. This work offers an efficient and sustainable route for co-producing fermentable sugars and functional lignin-based materials, contributing to a circular bioeconomy.

Synergistic release of lignin-carbohydrate structure by Lewis acid cations and anions to enhance delignification in deep eutectic solvents

Lewis acids are commonly used in deep eutectic solvents (DESs) to enhance delignification in lignocellulose pretreatment, though the mechanism is not well understood. This study compares the effects of alkali metal chlorides, acidic metal chlorides, and acidic metal non-chlorides on DESs delignification, focusing on metal ions and DESs properties. Results indicate that delignification enhancement follows the order: acidic metal chlorides > acidic metal non-chlorides > alkali metal chlorides. Key factors include pH (Pearson correlation coefficient: -0.88) and hydrogen bond donor activity (correlation: 0.91), and other DESs properties, such as viscosity, surface tension, hydrogen bond acceptor activity, and polarity, provide limited explanatory for delignification performance. The anion (Cl-) forms hydrogen bonds with lignin and lignin-carbohydrate complexes (LCCs) hydroxyl groups and further participates in ether bond cleavage. The destruction of β-O-4 linkages in recovered lignin confirms this finding, alongside the disruption of LCCs. Cations primarily facilitate the hydrolysis of hemicellulose glycosidic bonds by directly cracking and lowering the bond energy (-3.02 kJ/mol). This leads to the release and further degradation of LCCs, especially in γ-ester, p-coumaric acid, and ferulic acid components. These findings provide insight into Lewis acid-enhanced DESs delignification mechanisms.

Acidic and alkaline deep eutectic solvents pretreatment of Macadamia nutshells for production of cellulose nanofibrils and lignin nanoparticles

This study explored a facile method for converting macadamia nutshells into bio-based nanomaterials, including cellulose nanofibers (CNFs) and lignin nanoparticles (LNPs), through deep eutectic solvent (DES) pretreatment coupled with a nanofabrication strategy. Comparisons of the physicochemical, morphological, and structural properties of the CNF and LNPs produced through acidic choline chloride/oxalic acid dihydrate (ACDES) and alkaline K2CO3/glycerol DES (ALDES) pretreatments were conducted using SEM, TEM, FTIR, XRD, TGA, GPC and 2D NMR. The CNFs obtained from ACDES pretreatment (ACCNFs) exhibited uniform and long filament-like structures with shorter whisker-like nanocrystals. Conversely, the CNFs produced with the ALDES pretreatment (ALCNFs) displayed irregular aggregates and nanofibril bundles. Additionally, the ACCNFs demonstrated higher crystallinity and contained small amounts of the oxalate half-ester compare to ALCNFs. During ACDES pretreatment, a large proportion of β-O-4, β-5, and β-β linkages in lignin disrupted and re-condensed to form lignin substructures, resulting in the assembly of cluster-like lignin nanoparticles pretreated with ACDES (ACLNP) aggregates. In contrast, lignin nanoparticles pretreated with ALDES (ALLNP) exhibited uniform nanospherical shapes because of the preservation of β linkages in lignin during the ALDES pretreatment. This work not only broadens the fabrication strategies for CNF and LNPs but also offered a promising approach for the valorization of lignocellulosic agricultural wastes.

Nanocellulose separation from barley straw via ultrasound-assisted choline chloride - Formic acid deep eutectic solvent pretreatment and high-intensity ultrasonication

The present study aims at investigating the application of ultrasound assisted choline chloride (ChCl) - formic acid (FA) deep eutectic solvent (DES) pretreatment of Barley straw. In addition, the efficiency of a wet grinding followed by high intensity ultrasound (HIUS) treatment for production of cellulose nanofibers (CNF) has been evaluated. The DES (using ChCl: FA at 1:9 M ratio) treatment at 45 kHz ultrasound frequency and 3 h of treatment duration resulted in 84.68 ± 1.02 % and 82.96 ± 0.79 % of lignin and hemicellulose solubilisation, respectively. The purification of DES treated solid residue resulted in cellulose with more than 90 % purity. Further, 10 min of wet grinding followed by 40 min of HIUS treatment resulted in more than 80 % nano-fibrillation efficiency. The produced CNF had diameters less than 100 nm in number size distribution and type I cellulose structure. This study confirmed that the developed process offers a sustainable method for producing nanocellulose from agricultural waste.

Lignin Nanoparticles: Transforming Environmental Remediation

In the face of escalating environmental challenges driven by human activities, the quest for innovative solutions to counter pollution, contamination, and ecological degradation has gained paramount importance. Traditional approaches to environmental remediation often fall short in addressing the complexity and scale of modern-day environmental problems. As industries transition towards sustainable paradigms, the exploration of novel materials and technologies becomes crucial. Lignin nanoparticles have emerged as a promising avenue of exploration in this context. Once considered a mere byproduct, lignin's unique properties and versatile functional groups have propelled it to the forefront of environmental remediation research. This review paper delves into the resurgence of lignin from an environmental perspective, examining its pivotal role in carbon cycling and its potential to address various environmental challenges. The paper extensively discusses the synthesis, properties, and applications of lignin nanoparticles in diverse fields such as water purification and soil remediation. Moreover, it highlights the challenges associated with nanoparticle deployment, ranging from Eco toxicological assessments to scalability issues. Multidisciplinary collaboration and integration of research findings with real-world applications are emphasized as critical factors for unlocking the transformative potential of lignin nanoparticles. Ultimately, this review underscores lignin nanoparticles as beacons of hope in the pursuit of cleaner, healthier, and more harmonious coexistence between humanity and nature through innovative environmental remediation strategies.

A designed ZrOCl2/ethylene glycol deep eutectic solvent for efficient lignocellulose valorization

Deep eutectic solvents (DESs) hold great potential in biorefining because they can efficiently deconstruct the recalcitrant structure of lignocellulose. In particular, inorganic salts with Lewis acids have been proven to be effective at cleaving lignin-carbohydrate complexes. Herein, a Zr-based DES system composed of metal chloride hydrate (ZrOCl2·8H2O) and ethylene glycol (EG) was designed and used for poplar powder pretreatment. Zr4+-based salts provide sufficient acidity for lignocellulose depolymerization. The acidity of the DES was analysed by the Kamlet-Taft solvatochromic parameter, and the results demonstrated that the acidity can be regulated by the DES composition. Under the optimum conditions (ZrOCl2·8H2O:EG molar ratio of 1:2), the DES pretreatment removes nearly 100 % hemicellulose and 94.7 % lignin. The recovered lignin exhibited a low polydispersity of 1.7. The cellulose residues deliver an efficiency of 94.4 % upon enzymatic digestion. Moreover, the DES can be easily recovered with high yield and purity, and the recycled DES still maintains high delignification and enzymatic hydrolysis efficiencies. The proposed DES pretreatment technology is promising for biomass valorization.

Effect of Quorum Sensing Molecules on the Quality of Bacterial Nanocellulose Materials

Bacterial nanocellulose (BNC) biofilms, produced by various bacterial species, such as Gluconacetobacter xylinus, represent a highly promising multifunctional material characterized by distinctive physiochemical properties. These biofilms have demonstrated remarkable versatility as nano biomaterials, finding extensive applications across medical, defense, electronics, optics, and food industries. In contrast to plant cellulose, BNC biofilms exhibit numerous advantages, including elevated purity and crystallinity, expansive surface area, robustness, and excellent biocompatibility, making them exceptional multifunctional materials. However, their production with consistent morphological properties and their transformation into practical forms present challenges. This difficulty often arises from the heterogeneity in cell density, which is influenced by the presence of N-acyl-homoserine lactones (AHLs) serving as quorum sensing signaling molecules during the biosynthesis of BNC biofilms. In this study, we employed surface characterization methodologies including scanning electron microscopy, energy-dispersive spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and atomic force microscopy to characterize BNC biofilms derived from growth media supplemented with varying concentrations of distinct N-acyl-homoserine lactone signaling molecules. The data obtained through these analytical techniques elucidated that the morphological properties of the BNC biofilms were influenced by the specific AHLs, signaling molecules, introduced into the growth media. These findings lay the groundwork for future exploration of leveraging synthetic biology and biomimetic methods for tailoring BNC with predetermined morphological properties.

Cellulose-reinforced highly stretchable and adhesive eutectogels as efficient sensors

A cellulose-reinforced eutectogel was constructed by deep eutectic solvent (DES) and cotton linter cellulose. Cellulose was dispersed in the ternary DES consisting of acrylic acid, choline chloride and AlCl3·6H2O. The photoinitiator was then introduced into the system to in situ polymerize acrylic acid monomer to form transparent and ionic conductive eutectogels while keeping all the DES. The crosslinks formed by Al3+ induced ionic bonds and reversible links formed by hydrogen bonds give the eutectogels high stretchability (3200 ± 200 % tensile strain), self-adhesive (52.1 kPa to glass), self-healing and good mechanical strength (670 kPa). The eutectogels were assembled into sensors and epidermal patch electrodes that demonstrated high quality human motion sensing and physiological signal detection (electrocardiogram and electromyography). This work provides a facile way to design flexible electronics for sensing.

Process design for acidic and alcohol based deep eutectic solvent pretreatment and high pressure homogenization of palm bunches for nanocellulose production

This research aimed to study on nanocellulose production from palm bunch using process design and cost analysis. Choline chloride based deep eutectic solvent pretreatment was selected for high-purity cellulose separation at mild condition, followed by nano-fibrillation using mechanical treatment. Three types of choline chloride-based deep eutectic solvents employing different hydrogen-bond donors (HBDs) namely lactic acid, 1,3-butanediol and oxalic acid were studied. The optimal cellulose extraction condition was choline chloride/lactic acid (ChLa80C) pretreatment of palm empty bunch at 80 °C followed by bleaching yielding 94.96%w/w cellulose content in product. Size reduction using ultrasonication and high-pressure homogenization produced nanocellulose at 67.12%w/w based on cellulose in raw material. Different morphologies of nanocellulose were tunable in the forms of nanocrystals, nano-rods and nanofibers by using dissimilar deep eutectic solvents. This work offered a sustainable and environmentally friendly process as well as provided analysis of DES pretreatment and overview operating cost for nanocellulose production. Application of nanocellulose for the fabrication of highly functional and biodegradable material for nanomedicine, electronic, optical, and micromechanical devices is achievable in the near future.