Structure investigation of light-colored lignin extracted by Lewis acid-based deep eutectic solvent from softwood

Fast and sustainable extraction of light-colored lignin using oxalic acid dihydrate: Toward structural elucidation and UV/oxidation resistance

Lignin, an abundant and complex biopolymer, offers significant potential for high-value applications in diverse industries due to its antioxidant and UV-absorbing properties. However, its utilization in cosmetic formulations, particularly sunscreens, is impeded by its dark coloration. Herein, this study introduced an innovative approach for extracting light-colored lignin with well-preserved structure from wheat straw using oxalic acid dihydrate (OAD) under mild conditions. The OAD method significantly improved lignin color, accelerated the extraction process (within 5 min), and emphasized environmental sustainability, representing a marked improvement over traditional technique. Lignin isolated by the OAD method achieved yields up to 91.24 %, with an attractive light color and elevated purity. Comprehensive structural analyses revealed a substantial enrichment in phenolic hydroxyl groups and an advantageous S/G ratio, indicating superior antioxidant and UV-blocking efficacy. The antioxidant capacity, evaluated through DPPH radical scavenging assays, was exceptional, with an IC50 value below 0.1 mg/mL. Moreover, the addition of 5 % OAD-extracted lignin to pure cream indicated that SPF (SPFinvitro = 7.52) was higher than P25 (SPFinvitro = 5.92). This study underscores a highly efficient and environmentally benign method for producing premium, light-colored lignin, advancing its application in natural, sustainable cosmetic formulations.

Extracting light-colored lignin with high phenolic-OH from poplar by ultrasonic-assisted formic acid/phenol treatment to prepare transparent lignin/cellulose composite film

Lignin that has inherent antioxidant and UV absorption capacity can be incorporated with cellulose to prepare functional composite film. However, the dark color and low film-forming ability of industrial lignin limit its application in high-quality transparent films. In this work, ultrasound-assisted formic acid/phenol treatment (uFAPT) was used to extract phenolated and low-condensed lignin from poplar in view of the lignin priority principle. The structural characteristics of the isolated lignin were comprehensively clarified and the light-colored lignin with high phenolic hydroxyl was used to prepare lignin/cellulose composite film. The results showed that in-situ phenolation of lignin inhibited the lignin recondensation and the formation of Hibbert' ketone structure, resulting in a high yield of isolated lignin. The phenolated lignin had a high lightness, high phenolic hydroxyl content, low molecular weight and polydispersity, conferring the lignin/cellulose film a good transparency even at a high lignin loading. The incorporation of phenolated lignin not only significantly boosted the film's antioxidant capacity, UV shielding capability, hydrophobicity and water vapor barrier performance but also maintenance its tensile strength. Given above impressive properties, the lignin/cellulose film holds vast potential for applications in the realm of color restriction and food packaging, etc.

Deep eutectic solvent pretreatment of oil palm biomass: Promoted lignin pyrolysis and enzymatic digestibility of solid residues

Herein, choline chloride/oxalic acid (ChCl/OA) and choline chloride/oxalic acid/ethylene glycol (ChCl/OA/EG) pretreatments of oil palm empty fruit bunches (EFB) and mesocarp fibers (MSF) were conducted to achieve protection of the lignin structure, while improving the enzymatic efficiency of the solid residues. Under the operating conditions of 90 °C and 6 h, ChCl/OA/EG demonstrated a higher lignin extraction selectivity and obtained solid residues with higher hemicellulose content compared to ChCl/OA. The digestibility of glucan and xylan in solid residues obtained using ChCl/OA/EG achieved 98.56 % and 95.63 %, respectively, for EFB and 75.95 % and 88.60 %, for MSF. Uncondensed lignin enriched with 71.79-81.61 % of β-O-4 bonds was obtained from EFB and MSF using ChCl/OA/EG. 2D HSQC NMR and the density functional theory calculation confirmed that substituting the lignin Cα position by ethylene glycol changed the local potentials of the β-O-4 bonds, impeding the attack of protons (H+). The higher β-O-4 linkage content in ChCl/OA/EG-Ls led to the formation of several oxygenated alkyl methoxy phenols and alkyl methoxy phenols were promoted during the pyrolysis. Moreover, molecular dynamics simulations showed that the main factor affecting lignin extraction and dissolution in this study was the diffusion coefficient of lignin in DESs.

Switchable Solvent for Separation and Extraction of Lignin from Lignocellulose Biomass: An Investigation of Chemical Structure and Molecular Weight

Lignin, the most abundant natural aromatic polymer, holds considerable promise for applications in various industries. The primary obstacle to the valorization of lignin into useful materials is its low molecular weight and diminished chemical reactivity, attributable to its intricate structure. This study aimed to treat lignocellulosic biomass using a switchable solvent (DBU-HexOH/H2O) derived from the non-nucleophilic superbase 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU), which efficiently separates and extracts lignin from poplar wood. Additionally, it sought to characterize fundamental properties of the extracted switchable solvent lignin (SSL) and propose a mechanism for its separation. In comparison to milled wood lignin, SSL exhibits a greater molecular weight, superior homogeneity, and enhanced stability. The SSL sample was analyzed using spectroscopies including infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The findings indicated that the structure of SSL was preserved, with the switchable solvent primarily cleaving the C-C and α-O-4 bonds, resulting in a low hydroxyl content, an elevated H/C ratio, and a reduced O/C ratio. The SSL was successfully prepared to lignin nanoparticles (LNPs) with size range of 531-955 nm. This paper presents a technique for processing lignocellulosic biomass using a switchable solvent, highlighting advancements in lignin's structure and enhancing its use in the chemical sector.

Boron Lewis Acid Extraction of Wood Generates High Quality Lignin

The separation of lignocellulose into lignin, cellulose, and hemicellulose without significantly altering the chemical structures of these component biopolymers remains a modern chemical challenge. Lignin, in particular, has potential as a highly valuable feedstock material but remains underutilized due to the difficulty of generating lignin with low modification and condensation. This work investigates the lignin-rich solids ("boron lignin") generated from a previously reported boron Lewis acid-mediated lignocellulose separation and concludes that (1) boron Lewis acid extraction removes 80-85% of carbohydrates from the original lignocellulose sample, and (2) the resulting lignin possesses a low condensation level and high similarity to native lignin structure. Residual carbohydrate assessment, depolymerization efficiency analyses, heteronuclear single quantum coherence (HSQC) and solid-state nuclear magnetic resonance (NMR) analyses are discussed, including benchmarking results with alternate lignin sources known to possess low and high condensation levels. Further, two different wood sources (white pine, a softwood, and beechwood, a hardwood) were employed to generate lignin samples. Depolymerization of a white pine-derived boron-lignin produced 47% (±9.5) of extractable monomers, which compares well to a state-of-the-art method to generate low condensed lignin (56 ± 7.8%). An unexpected instability of the oil sample was observed following hydrogenolysis of boron lignin generated from beechwood. Dramatic color changes coupled with precipitation and lowered monomer yields were observed when samples were aged (11% decrease) or concentrated (30% decrease). Based on NMR spectroscopic analyses, this instability is postulated to arise due to boron-mediated demethylation of methoxy sites on the lignin scaffold.

Lignin valorization through the oxidative activity of β-etherases: Recent advances and perspectives

The increasing interest in lignin, a complex and abundant biopolymer, stems from its ability to produce environmentally beneficial biobased products. β-Etherases play a crucial role by breaking down the β-aryl ether bonds in lignin. This comprehensive review covers the latest advancements in β-etherase-mediated lignin valorization, focusing on substrate selectivity, enzymatic oxidative activity, and engineering methods. Research on the microbial origin, protein modification, and molecular structure determination of β-etherases has improved our understanding of their effectiveness. Furthermore, the use of these enzymes in biorefinery processes is promising for enhancing lignin breakdown and creating more valuable products. The review also discusses the challenges and future potential of β-etherases in advancing lignin valorization for biorefinery applications that are economically viable and environmentally sustainable.

Efficient extraction of lignin from moso bamboo by microwave-assisted ternary deep eutectic solvent pretreatment for enhanced enzymatic hydrolysis

Applications of deep eutectic solvent (DES) systems to separate lignocellulosic components are of interest to develop environmentally friendly processes and achieve efficient utilization of biomass. To enhance the performance of a binary neutral DES (glycerol:guanidine hydrochloride), various Lewis acids (e.g., AlCl3·6H2O, FeCl3·6H2O, etc.) were introduced to synthesize a series of ternary DES systems; these were coupled with microwave heating and applied to moso bamboo. Among the ternary DES systems evaluated, the FeCl3-based DES effectively removed lignin (81.17%) and xylan (85.42%), significantly improving enzymatic digestibility of the residual glucan and xylan (90.15% and 99.51%, respectively). Furthermore, 50.74% of the lignin, with high purity and a well-preserved structure, was recovered. A recyclability experiment showed that the pretreatment performance of the FeCl3-based DES was still basically maintained after five cycles. Overall, the microwave-assisted ternary DES pretreatment approach proposed in this study appears to be a promising option for sustainable biorefinery operations.

Sugarcane Light-Colored Lignin: A Renewable Resource for Sustainable Beauty

Lignin has emerged as a promising eco-friendly multifunctional ingredient for cosmetic applications, due to its ability to protect against ultraviolet radiation and its antioxidant and antimicrobial properties. However, its typical dark color and low water solubility limit its application in cosmetics. This study presents a simple process for obtaining light-colored lignin (LCLig) from sugarcane bagasse (SCB) alkaline black liquor, involving an oxidation treatment with hydrogen peroxide, followed by precipitation with sulfuric acid. The physico-chemical characterization, antioxidant and emulsifying potential of LCLig, and determination of its safety and stability in an oil-in-water emulsion were performed. A high-purity lignin (81.6%) with improved water solubility was obtained, as a result of the balance between the total aromatic phenolic units and the carboxylic acids. In addition, the antioxidant and emulsifying capacities of the obtained LCLig were demonstrated. The color reduction treatment did not compromise the safety of lignin for topical cosmetic applications. The emulsion was stable in terms of organoleptic properties (color, pH, and viscosity) and antioxidant activity over 3 months at 4, 25, and 40 °C.

Fractionation and evaluation of light-colored lignin extracted from bamboo shoot shells using hydrated deep eutectic solvents

In this study, light-colored lignin was extracted from bamboo shoot shells (BSS) using a hydrated deep eutectic solvent (DES) pretreatment. The hydrated DES used in pretreatment consist of formic acid, benzyl triethylammonium chloride (BTEAC) and water. The pretreatment using a hydrated DES containing 30% water (H30) demonstrate efficient delignification (82.9%). Additionally, the hydrated DES protected the β-O-4 linkage from excessive cleavage and recondensation as well as keep the light-colored of lignin. Moreover, the hydrated DES extracted lignin exhibits superior antioxidant performance and tyrosinase inhibitory capacity compared to the control. Notably, incorporating 5% lignin of H30-extracted lignin into a commercial suncream led to a remarkable enhancement of the SPF value, elevating from 14.8 to 32.6. In summary, the proposed hydrated DES pretreatment method offers significant benefits for extracting light-colored lignin, thereby promoting the multifunctional application of lignin in cosmetics.