The structure and properties of lignin isolated from various lignocellulosic biomass by different treatment processes

Insights on comprehensive characterization of distinct growth stages of Sterculia foetida pod as a potential feedstock for bioethanol production

Lignocellulosic biomass explores a sustainable and renewable energy source that could provide a suitable solution to energy demands. However, diversity is the main obstacle that hinders the biorefinery approach to bioethanol production. In this study, the non-edible feedstock, Sterculia foetida pod, green-colored skin (GSFP), and brown-colored skin (BSFP) were used as feedstock for the production of bioethanol. To examine the comprehensive characterization of selected biomass, namely BSFP and GSFP, the various methods, namely physicochemical analysis, proximate analysis, ultimate (CHNS) analysis, bulk density, and calorific value were employed. The functional group analysis, thermal stability, surface morphology, and crystallinity index for biomasses were characterized by FTIR spectroscopy, Thermo-gravimetric (TGA) analysis, scanning electron microscope (SEM), and XRD analysis. The elemental and chemical composition of GSFP and BSFP were extensively evaluated using different methods. The value-added precursors, namely cellulose and lignin isolated from GSFP and BSFP. The cellulose content in GSFP and BSFP pods was found to be 35.28 ± 3.39% and 33.95 ± 4.49% and the lignin content was 17.37 ± 3.54% and 20.79 ± 8.78% respectively. The obtained cellulose from GSFP and BSFP was subjected to two-step acid hydrolysis on different SL ratio (1:10-5:10) to prepare fermentable sugars at different concentration (g/L). Based on the different sugar concentration, the bioethanol concentration (0.91 to 18.78 g/L; 0.23 to 12.23 g/L) and specific bioethanol yield (0.44 to 1.52 g/g; 0.13 to 1.55 g/g) increased for both BSFP and GSFP respectively.

Lignin-based biochar with improved properties derived from the microbial combined chemical pretreatment of corn straw for efficient antibiotic removal

In this study, straw lignin was separated from corn straw by combining microbial treatment with ρ-TsOH organic acid extraction for the first time, and lignin-derived biochars were prepared by carbonation-activation. The results showed that the extraction rate of lignin and the physicochemical properties of related biochars were improved greatly by microbial treatment. The specific surface areas of lignin biochar obtained after combined pre-treatment with Aspergillus niger, Myrothecium verrucaria, and Trichoderma reesei, (BNL, BML, and BTL) were 2348, 2849 and 3008 m2 g-1, respectively, and the total pore volumes were 0.8989, 0.9411, and 1.2621 cm3 g-1, which were significantly higher than the 2292 m2 g-1 and 0.7786 cm3 g-1 of the control group BCL (biochar prepared from lignin extracted from raw straw). In adsorption experiments by using tetracycline hydrochloride and sodium sulfadiazine as antibiotic models, the maximum adsorption capacities of all lignin-derived biochars (BML, BTL, and BNL) were greater than that of most other adsorbents including BCL. We hope this work could provide a new strategy for efficiently using microbial treatment technology to improve the conversion of lignocellulosic resources.

Extraction of lignin from sustainable lignocellulosic food waste resources using a green deep eutectic solvent system and its property characterization

Food waste, an abundant and widely available lignocellulosic biomass is a potential feedstock for recovering value-added products like lignin possessing various valuable properties through valorisation thereby minimizing its disposal and hence detrimental impact to the environment. The present study investigates the efficacy of the choline chloride-oxalic acid DES system for extracting lignin biomaterial from a variety of food wastes namely potato peel, onion skin, tea residues, banana peel and pomegranate peel wastes and its properties. The extraction experiments were carried out at 100°C for 6h using DES with a solid-to-liquid ratio of 1: 10 (w/v). The yield and purity of the extracted lignin from different biowastes were determined. A varied yield and purity of lignin was obtained depending on the sources of waste biomass. However, the highest lignin yield of 22.439 ± 4.38 % and purity of 77 ± 1.95 % was obtained with pomegranate peel. A comparable lignin yield (21.348 ± 2.40 %) and purity (75 ± 1.26 %) was also achieved with banana peel. UV-Visible and FTIR analyses revealed the existence of aromatic and major functional groups of lignin. XRD analysis confirmed its amorphous nature and its spherical or ellipsoidal morphology revealed by FESEM image analysis. The presence of hydroxyl ions, phenols, and carboxylic acids, and protons in the methoxy group and aliphatic and aromatic moieties in the lignin were identified by negative zeta potential values and 1H NMR spectra analysis respectively. The quantity of major linkages like β-O-4', β - 5' and β - β' in the lignin was determined by 2D-HSQC NMR. The lignin also exhibited antimicrobial and antioxidant activities. The elemental composition and higher heating values were determined by CHNSO analysis. Overall, pomegranate and banana peels are the most prospective food wastes found in this study for extracting lignin with high yield. The study further demonstrated the potentiality of the green DES for food waste valorisation to extract lignin.

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.

Optimizing corncob pretreatment with eco-friendly deep eutectic solvents to enhance lignin extraction and cellulose-to-glucose conversion

Deep eutectic solvents (DES) are an eco-friendly, cost-effective alternative to traditional ionic liquids for biomass pretreatment, with unique characteristics encompassed by hydrogen bond donor (HBD), the molar ratio of hydrogen bond acceptor (HBA) to HBD, temperature, and time affecting efficiency. Despite its potential, a comprehensive study exploring the interplay of these factors is limited. This study explores the optimization of pretreatment variables using choline chloride/lactic acid (1:5) via the response surface method (RSM). It aims to evaluate the effects of time and temperature on lignin extraction, cellulose-to-glucose conversion, and hemicellulose removal. Employing a 22 central composite design with temperature (80-140 °C) and time (2-6 h) as variables, optimal conditions were 123 °C for 6 h. Results include 90.08±1.42 % lignin extraction, 68.77±6.9 % cellulose-to-glucose conversion, and 77.34±0.85 % hemicellulose removal, with 52.52±8.07 % lignin recovery. The fractions of pretreated CC and lignin recovered in the optimal condition found were characterized by X-ray diffraction (XDR), Fourier transform infrared spectroscopy (FTIR), 1H, 13C, 2D-HSQC NMR spectroscopy, Thermogravimetric analysis (TGA/DTG), Gel Permeation Chromatography (GPC) to elucidate chemical characteristics of the materials obtained and facilitate downstream valorization. High efficiency was achieved in lignin extraction and cellulose conversion, and addressing solvent viscosity and DES recycling will further enhance the potential for industrial scalability.

Insights into the pelletization behaviors of artificial lignocellulosic biomass based on cellulose, hemicellulose and lignin: A simplex lattice mixture design approach

The use of high quality densified pellet as an alternative to traditional fossil fuels is a promising avenue of research due to their interesting higher density, superior heating values, and enhanced combustion performance. However, little is known about the pelletization behaviors from the aspect of lignocellulosic biomass fundamental components (cellulose, hemicellulose and lignin) and their mixtures. This study presents an artificial biomass developed based on cellulose, hemicellulose and lignin using a simplex lattice design approach, aiming to understand the detailed role of major components and its effects on pellet quality. The correlation between the experimental data obtained from the simplex lattice design and the predicted response parameters were effectively explained by Scheffé's special cubic model, with a coefficient of determination beyond 90 %. Parameter estimates showed a significant synergetic effect of each components for density and Meyer hardness. Results revealed that xylan may be softened like lignin and thereby potentially act as binder. The use of a high cellulose concentration resulted in enhanced pellet strength by acting as a supporting skeleton. Xylan and cellulose played a major role in the thermal degradation of densified pellets. Based on the results obtained, the optimal components composition was determined to be 34.5 % lignin, 36.3 % cellulose, and 29.2 % xylan. Under this, the pellet exhibited the best density and Meyer hardness beyond 1500 kg/m3 and 80 N/mm2, respectively. The results provide a foundation for future efforts to be able to predict pellet properties from the perspective of biomass composition.

Research Status of Lignin-Based Polyurethane and Its Application in Flexible Electronics

Polyurethanes (PU) have drawn great attention due to their excellent mechanical properties and self-healing and recyclable abilities. Lignin is a natural and renewable raw material in nature, composed of a large number of hydroxyl groups, and has a great potential to replace petroleum polyols in PU synthesis. This review summarizes the recent advances in modification methods such as the liquefaction, alkylation, and demethylation of lignin, and a systematic analysis of how to improve the reactivity and monomer substitution of lignin during polyurethane synthesis for the green manufacturing of high-performance polyurethanes was conducted. Polyurethane can be used in the form of films, foams, and elastomers instead of conventional materials as a dielectric or substrate material to improve the reliability and durability of flexible sensors; this review summarizes the green synthesis of polyurethanes and their applications in flexible electronics, which are expected to provide inspiration for the wearable electronics sector.

Unlocking the potential of phenolated kraft lignin as a versatile feed additive

Lignin, a renewable natural antioxidant and bacteriostat, holds promise as a versatile, cost-effective feed additive. However, traditional industrial lignin faces limitations, including low reactivity, poor uniformity, and unstable properties, necessitating chemical modification. Complex modification methods pose economic and toxicity challenges, so this study adopted a relatively simple alkali-catalyzed phenolization approach, using phenol, catechol, and pyrogallol to modify kraft lignin, and characterized the resulting products using various techniques. Subsequently, their antioxidant, antibacterial, adsorption properties for heavy metal ions and mycotoxins, growth-promoting properties, and antiviral abilities were assessed. The phenolation process led to lignin depolymerization and a notable increase in phenolic hydroxyl content, particularly in pyrogallol-phenolated lignin (Py-L), rising from 3.08 to 4.68 mmol/g. These modified lignins exhibited enhanced antioxidant activity, with over 99 % inhibition against E. coli and S. aureus, and remarkable adsorption capacities for heavy metal ions and mycotoxins. Importantly, Py-L improved the growth performance of mice and reduced influenza mortality. Furthermore, density functional theory calculations elucidated the mechanism behind the enhanced antioxidant properties. This study presents a promising avenue for developing versatile feed additives to address challenges related to animal feed antioxidant supplementation, bacterial control, and growth promotion.

Extraction of homogeneous lignin oligomers by ozonation of Miscanthus giganteus and vine shoots in a pilot scale reactor

Lignin, a complex phenolic polymer crucial for plant structure, is mostly used as fuel but it can be harnessed for environmentally friendly applications. This article explores ozonation as a green method for lignin extraction from lignocellulosic biomass, aiming to uncover the benefits of the extracted lignin. A pilot-scale ozonation reactor was employed to extract lignin from Miscanthus giganteus (a grass variety) and vine shoots (a woody biomass). The study examined the lignin extraction and modification of the fractions and identified the generation of phenolic and organic acids. About 48 % of lignin was successfully extracted from both biomass types. Phenolic monomers were produced, vine shoots yielding fewer monomers than Miscanthus giganteus. Ozonation generated homogeneous lignin oligomers, although their molecular weight decreased during ozonation, with vine shoot oligomers exhibiting greater resistance to ozone. Extracted fractions were stable at 200 °C, despite the low molecular weight, outlining the potential of these phenolic fractions.

Synergistic microwave and acidic deep eutectic solvent-based pretreatment of Theobroma cacao pod husk biomass for xylooligosaccharides production

The bioconversion of lignocellulosic biomass into novel bioproducts is crucial for sustainable biorefineries, providing an integrated solution for circular economy objectives. The current study investigated a novel microwave-assisted acidic deep eutectic solvent (DES) pretreatment of waste cocoa pod husk (CPH) biomass to extract xylooligosaccharides (XOS). The sequential DES (choline chloride/citric acid, molar ratio 1:1) and microwave (450W) pretreatment of CPH biomass was effective in 67.3% xylan removal with a 52% XOS yield from total xylan. Among different XOS of varying degrees of polymerization, a higher xylobiose content corresponding to 69.3% of the total XOS (68.22 mg/g CPH) from liquid fraction was observed. Enzymatic hydrolysis of residual xylan from pretreated CPH biomass with low commercial xylanase (10 IU/g) concentration yielded 24.2% XOS. The MW-ChCl/citric acid synergistic pretreatment approach holds great promise for developing a cost-effective and environmentally friendly method contributing to the sustainable production of XOS from agricultural waste streams.

Structure and thermal properties of cellulose nanofibrils extracted from alkali-ultrasound treated windmill palm fibers

Windmill palm, a tree species that is native to China, has gained attention with regard to the production of substantial amounts of biomass fibers via yearly pruning. This study investigates the structure and thermal properties of cellulose nanofibrils (CNFs) obtained from windmill palm biomass, with the goal of promoting the usage of these CNFs. Alkali-ultrasound treatments are employed herein to prepare samples of the CNFs. The micromorphology of the prepared samples is observed using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Furthermore, X-ray diffraction analysis is used to examine the aggregated structure of the samples, and thermogravimetric analysis is used to investigate their thermal properties. Results indicate that during alkali hydrolysis when obtaining CNFs, the fiber cell wall exhibits distinct spiral cracking. The diameter of the obtained nanocellulose is <90 nm. The removal of lignin and hemicellulose materials from the fiber cell enhances the crystallinity of CNFs to as high as 60 %, surpassing that of windmill palm single fibers. The thermal decomposition temperatures of the CNFs are found to be 469 °C and 246 °C for the crystalline and amorphous regions, respectively.

Switchable Deep Eutectic Solvents for Lignin Dissolution and Regeneration

Deep eutectic solvents (DESs) are promising for lignin dissolution and extraction. However, they usually possess high polarity and are difficult to recycle. To overcome this drawback, a variety of switchable ionic liquids (SILs) composed of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and alcohols was synthesized and screened. According to the thermodynamic modeling suggestions, the selected DBU-HexOH SIL was coupled with hydrogen-bond donors to form switchable-DES (SDES) systems with moderated viscosity, conductivity, and pH while maintaining switchability. The SDESs produced a well-improved lignin and lignin model compound solubility compared with those of SILs; charging CO2 into SDES (SDESCO2) caused a further increase in solubility. The solubility (25 °C) of syringic acid, ferulic acid, and milled wood lignin in SDESCO2 reached 230.57, 452.17, and 279.12 mg/g, respectively. Such SDES-dissolved lignin can be regenerated using acetone as an anti-solvent. The SDES-regenerated lignin exhibited a well-preserved structure with no noticeable chemical modifications. Furthermore, the SDESCO2 lignin possessed a higher molecular weight (Mw = 10,340 g/mol; Mn = 7672 g/mol), improved uniformity (polydispersity index = 1.35), and a higher guaiacyl lignin unit content compared with the original milled wood lignin. The SDES system proposed in the present work could benefit the fractionation of lignin compounds and facilitate downstream industrial processes.