Lignin Structure Research Articles

Water effect on the characterization of 1-butyl-3-methylimidazolium hydrogen sulfate and lignin dissolution

ABSTRACT Lignin dissolution plays an important role in the conversion process of lignin. This work focused on the lignin dissolution in a binary mixture of 1-butyl-3-methylimidazolium hydrogen sulfate([BMIM]HSO4) and water. To understand the lignin dissolution behavior in the binary mixture of [BMIM]HSO4/H2O, the molecular interactions of [BMIM]HSO4 and H2O were first investigated by simple methods based on the viscosity and UV spectra. Then three different lignin samples, enzymatic hydrolysis lignin, alkali lignin, and organosolv Lignin, were employed to investigate the dissolution ability of [BMIM]HSO4/water with different mass fraction of [BMIM]HSO4([BMIM]HSO4%). The molecular interactions and lignin solubility of [BMIM]HSO4/H2O strongly depended on the mass fraction of [BMIM]HSO4([BMIM]HSO4%). A turning point for the formation of bi-continuous system at [BMIM]HSO4% of 63% was observed by the changing trend of viscosity and UV absorption. [BMIM]HSO4/H2O with 60-90% of [BMIM]HSO4% had excellent ability to dissolve EHL, and achieved the maximum value at 70% of [BMIM]HSO4%. It was indicated that the bi-continuous [BMIM]HSO4/H2O was the most effective in lignin dissolution. Lignin was regenerated with a recovery rate of 94.29%. Compared the regenerated lignin and the raw lignin, [BMIM]HSO4 altered the arrangement structure of lignin without no changes in the chemical structures. This study provided ideas for the process design of lignin dissolution and conversion in the [BMIM]HSO4/H2O system.

Anaerobic fermentation of poplar processing residue to produce methane by alkaline hydrogen peroxide (AHP) pretreatment

ABSTRACT The study evaluated the effects of alkaline hydrogen peroxide (AHP) pretreatment on poplar processing residue for methane production. The delignification of poplar processing residue was used as the basis for evaluation. The experiment considered the pretreatment time (0 h-24 h), the hydrogen peroxide (H2O2) concentration (0.5%-2.0%), and potassium hydroxide (KOH) concentration (1.0%-3.0%) at a temperature of 70°C. Subsequently, anaerobic fermentation experiments were conducted using the pretreated biomass with sludge as the inoculum under mesophilic temperature conditions (37 ± 1°C). The initial feedstock (poplar processing residue) contained 40.31 ± 0.06% cellulose, 31.17 ± 1.59% lignin, and 14.85 ± 0.38% hemicellulose. The AHP pretreatment caused changes in the lignocellulosic content of the feedstock, particularly affecting the lignin structure compared to cellulose and hemicellulose. At a pretreatment time of 18 hours, temperature of 70°C, and concentrations of 2.0% H2O2 and 1.0% KOH, the AHP pretreatment resulted in a higher methane production of 237.4 mL per gram. These findings demonstrate that AHP pretreatment is an effective strategy for enhancing methane production from poplar.

Preparation and characterization of lignin-derived carbon aerogels.

Lignin is considered a valuable renewable resource for building new chemicals and materials, particularly resins and polymers. The aromatic nature of lignin suggests a synthetic route for synthesizing organic aerogels (AGs) similar to the aqueous polycondensation of resorcinol with formaldehyde (FA). The structure and reactivity of lignin largely depend on the severity of the isolation method used, which challenges the development of new organic and carbon materials. Resorcinol aerogels are considered a source of porous carbon material, while lignin-based aerogels also possess great potential for the development of carbon materials, having a high carbon yield with a high specific surface area and microporosity. In the present study, the birch hydrolysis lignin and organosolv lignin extracted from pine were used to prepare AGs with formaldehyde, with the addition of 5-methylresorcinol in the range of 75%-25%, yielding monolithic mesoporous aerogels with a relatively high specific surface area of up to 343.4m2/g. The obtained lignin-based AGs were further used as raw materials for the preparation of porous carbon aerogels (CAs) under well-controlled pyrolysis conditions with the morphology, especially porosity and the specific surface area, being dependent on the origin of lignin and its content in the starting material.

Starch biocomposites preparation by incorporating organosolv lignins from potato crop residues

Plastic wastes accumulated due to food packaging pose environmental threats. This study proposes biopolymeric films containing lignins extracted from potato crop residues (PCR) through organosolv treatment as a green alternative to non-degradable food packaging. The isolation process yielded 43.9 wt% lignins with a recovery rate of 73.5 wt% achieved under optimum conditions at 180 °C with 50 % v/v ethanol. The extracted lignins were then incorporated into a starch matrix to create biocomposite films. ATR-FTIR analysis confirmed interactions between the starch matrix and extracted lignins, and XRD analysis showed the amorphous structure of lignins, reducing film crystallinity. The addition of 1 wt% of extracted lignins resulted in a 87 % reduction in oxygen permeability, a 25 % increase in the thermal stability of the film, and a 78 % enhancement in antioxidant. Furthermore, introducing 3 wt% lignins led to the lowest water vapor transmission rate, measuring 9.3 × 10−7 kg/s·m2. Morphological studies of the films demonstrated a homogeneous and continuous structure on both the surface and cross-sectional areas when the lignins content was below 7 wt%. These findings highlight the potential of using organosolv lignins derived from potato crop residues as a promising additive for developing eco-friendly films designed for sustainable food packaging.

Investigation of lignin substructures participating in self-assembly for the synthesis of monodisperse lignin spherical particles

The intricate structure of lignin, characterized by a mix of hydrophilic components and hydrophobic structures from its aliphatic and aromatic constituents, poses challenges in creating monodisperse particles. This is due to the need for precise modulation of self-assembly kinetics. Herein, we explore a correlation between the substructure of lignin and its capacity for self-assembly. We have conducted an in-depth investigation into the interactions between hydrophilic groups, such as phenolic and aromatic-OH, and monolignols with interunit linkages that are involved in the formation of lignin particles (LPs). A high degree of hydrophilicity with a condensed structure is crucial for high supersaturation levels, which in turn determines the growth phase and leads to small LPs. An approach based on tailoring the supersaturation level which is contingent on the structural characteristics of extracted organosolv lignin was used to obtain remarkably uniform LPs with mean diameters of approximately 230 and 480 nm. The results of this study have the potential to serve as a foundation for the preparation of monodisperse LPs derived from various lignin sources as well as for the development of methods to extract lignin containing a specific chemical substructure.

Structure, flexibility and hydration properties of lignin dimers studied with Molecular Dynamics simulations

Abstract Lignin is an abundant polymer found in wood and grasses, but due to its heterogeneity and complex macromolecular structure it has been less utilized than cellulose. While the building blocks are known, the way they are linked is less understood. Here, Molecular Dynamics simulations were used to systematically characterize seven linkages found in native lignin. Their influence on lignin and water structure, and their interactions were analyzed. The study is limited to guaiacyl (G-G) dimers connected by the following common softwood linkages; 5-5′, 4-O-5′, α-O-4′, β-1′, β-5′, β-O-4′ and β-β′. The simulations show that the linkage has a significant effect on conformational preference and lignin-water interaction. Especially, the behavior of the β-O-4′ shows unique properties, both in terms of conformational freedom and interaction with water. Within the β-O-4′ dimer, π–π stacking between the aromatic rings is possible. The molecule has two distinct common conformations, one compressed and one extended. These preferences also lead to a different effect of β-O-4′ dimer on the surrounding water, where water is found close to the linkage itself but expelled from the aromatic rings to a larger extent than the other linkages. These findings are important for lignin solubility as well as its depolymerization mechanisms.

Quantitative analysis of the β-1 structure in lignin by administration of [ring-1-13C]coniferin

Abstract Lignin dimeric units are characterized by various inter-unit linkage types such as β-O-4, β-5, β-β, and β-1. Spirodienones are the native form of the β-1 structures, but the content in lignin has not been clarified. In this study, the ring-1-13C labeled coniferin was synthesized and administered to Ginkgo biloba shoots, obtaining ring-1 selectively labeled xylem samples. Enzymatically saccharified lignin (EL) samples were prepared from the xylem sample (400–600 µm distant region from the cambial zone), and solution-state quantitative 13C NMR and solid-state CP/MAS NMR measurements were conducted. Acetylated EL (ELAc) was also prepared from the xylem sample (600–800 µm distant region from the cambial zone), and solution-state quantitative 13C NMR and 1H–13C 2D NMR measurements were conducted. Difference spectra obtained by subtracting the unlabeled spectra from the ring-1 labeled spectra showed that the ring-1 was responsible for broad signals at 134 ppm and signals of the spirodienone structure at 56.11 ppm (in solid-state), 54.70 ppm (EL in solution-state), and 54.72 ppm (ELAc in solution-state). The ratio of spirodienone structure was evaluated as 0.68 % (EL) and 0.72 % (ELAc) by the solution-state quantitative 13C difference spectra, and 2.3 % (ELAc) by HSQC volume ratio of Cα′-H to G2-H.

3D printed lignin/polymer composite with enhanced mechanical and anti-thermal-aging performance

Lignin is the most abundant natural aromatic polymer globally but is still underutilized as a renewable material, even with its versatile properties. One approach to using lignin is to incorporate it in polymer composites, but this application is often limited by the poor mechanical performance of the resultant composite due to the poor interfacial adhesion. Following the structure–property relationship, stronger interactions were designed to be enhanced by alternating the functional groups of lignin. This study applied a demethylation method to hardwood lignin (Ori-Lig) to introduce more phenolic hydroxyl groups. Research studies with rheology behavior and molecular simulations demonstrated that an increased phenolic hydroxyl content could improve the adhesion between the modified lignin (OH-Lig) and the polymer matrix at the interface. The tensile performance of the samples from the fused depositional modeling (FDM) 3D printing technique was also improved due to the improved interfacial adhesion. Specifically, by adding 10 wt% of the modified lignin, the tensile strength of the 3D printed samples could reach 46.1 MPa (40.2 MPa of Polyamide 12, PA12), and Young’s Modulus could be improved to 1.73 GPa (1.48 GPa of PA12). OH-Lig also improved anti-aging performance so that the tensile strength of the OH-Lig composite after thermo-aging (100 h at 140 °C) remained ∼ 48 MPa. The enhanced mechanical performance with anti-aging properties indicated that the OH-Lig composite may replace PA12 to reduce the use of petrol-based materials. This work showed the method of purposefully designing and modifying lignin structures to fulfill the interaction requirements between lignin and polymer matrix. The as-prepared lignin could be used to prepare functional composites to achieve improved mechanical performance and targeted functions at the same time.

A density functional theory study on interactions in water-bridged dimeric complexes of lignin.

Lignin is the main plant cell wall component responsible for recalcitrance in the process of lignocellulosic biomass conversion into biofuels. The recalcitrance and insolubility of lignin in different reaction media are due in part to the hydrogen bonds and π interactions that hold syringyl (S) and guaiacyl (G) units together and promote the formation of stable water-bridged dimeric complexes (WBDCs): S⋯G and S⋯S, in native lignin. The current understanding of how each type of interaction influences the stability of these complexes within lignin native cell walls is still limited. Here, we found by DFT calculations that hydrogen bonding is more dominant than π-stacking interaction between aromatic rings of WBDCs. Although there is a stronger interaction of hydrogen bonds between subunits and water and higher π-stacking interaction in the S⋯S complex compared to the S⋯G complex, the former complex is less thermodynamically stable than the latter due to the entropic contribution coming from the methoxy substituents in the S-unit. Our results demonstrate that the methoxylation degree of lignin units does not significantly influence the structural geometries of WBDCs; if anything, an enhanced dispersion interaction between ring aromatics results in quasi-sandwich geometries as found in "coiled" lignin structures in the xylem tissue of wood. In the same way as that with ionic liquids, polar solvents can dissolve S-lignin by favorable interactions with the aliphatic hydroxyl group in the α-position as the key site or the aromatic hydroxyl group as the secondary site.

Utilising Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to track the oxidation of lignin by an alkaliphilic laccase.

Lignin is a complex heteroaromatic polymer which is one of the most abundant and diverse biopolymers on the planet. It comprises approximately one third of all woody plant matter, making it an attractive candidate as an alternative, renewable feedstock to petrochemicals to produce fine chemicals. However, the inherent complexity of lignin makes it difficult to analyse and characterise using common analytical techniques, proving a hindrance to the utilisation of lignin as a green chemical feedstock. Herein we outline the tracking of lignin degradation by an alkaliphilic laccase in a semi-quantitative manner using a combined chemical analysis approach using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterise shifts in chemical diversity and relative abundance of ions, and NMR to highlight changes in the structure of lignin. Specifically, an alkaliphilic laccase was used to degrade an industrially relevant lignin, with compounds such as syringaresinol being almost wholly removed (95%) after 24 hours of treatment. Structural analyses reinforced these findings, indicating a >50% loss of NMR signal relating to β-β linkages, of which syringaresinol is representative. Ultimately, this work underlines a combined analytical approach that can be used to gain a broader semi-quantitative understanding of the enzymatic activity of laccases within a complex, non-model mixture.

Lignin-based porous carbon adsorbents for CO2 capture.

A major driver of global climate change is the rising concentration of atmospheric CO2, the mitigation of which requires the development of efficient and sustainable carbon capture technologies. Solid porous adsorbents have emerged as promising alternatives to liquid amine counterparts due to their potential to reduce regeneration costs. Among them, porous carbons stand out for their high surface area, tailorable pore structure, and exceptional thermal and mechanical properties, making them highly robust and efficient in cycling operations. Moreover, porous carbons can be synthesized from readily available organic (waste) streams, reducing costs and promoting circularity. Lignin, a renewable and abundant by-product of the forest products industry and emerging biorefineries, is a complex organic polymer with a high carbon content, making it a suitable precursor for carbon-based adsorbents. This review explores lignin's sources, structure, and thermal properties, as well as traditional and emerging methods for producing lignin-based porous adsorbents. We examine the physicochemical properties, CO2 adsorption mechanisms, and performance of lignin-derived materials. Additionally, the review highlights recent advances in lignin valorization and provides critical insights into optimizing the design of lignin-based adsorbents to enhance CO2 capture efficiency. Finally, it addresses the prospects and challenges in the field, emphasizing the significant role that lignin-derived materials could play in advancing sustainable carbon capture technologies and mitigating climate change.

Choline and lactic acid covalently incorporate into the lignin structure during deep eutectic solvent pulping

We demonstrate the unique substituted nature of lignin following deep eutectic solvent pulping of plant biomass. The incorporation of novel lactic acid and choline based functionalities is highlighted, now calling for targeted DES lignin application.

Structure–reactivity relationships governing hydrothermal liquefaction of lignin from co-solvent enhanced lignocellulosic fractionation (CELF)

This study advances the fundamental understanding of the correlation between lignin structure and reactivity during hydrothermal liquefaction (HTL).

A high-performance lignin flow fuel cell based on self-generating electricity of lignin at low temperature via a privileged structure and redox chemistry

A lignin flow fuel cell is developed which can self-generate electricity via the privileged structure and redox chemistry of lignin without electron mediators and pre-reaction. It achieves high power density and long-term stability at room temperature.

Harnessing unconventional monomers to tailor lignin structures for lignocellulosic biomass valorization

Harnessing unconventional monomers to tailor lignin structures for lignocellulosic biomass valorization

Bio-bleaching of ankara pulp with xylanase-producing bacterial consortium for sustainable handmade paper production

The paper industry faces two critical challenges: the scarcity of raw materials and the environmental impact of chemical waste pollution. Addressing the first challenge involves harnessing alternative, sustainable raw materials, while the second challenge can be mitigated through the adoption of bio-bleaching processes, which significantly reduce chemical consumption while enhancing paper brightness and quality. This study proposes a solution to both challenges by using non-woody Calotropis procera (Ankara) and a xylanase-producing microbial consortium for sustainable handmade paper production, a combination not extensively explored in prior research. To evaluate this approach, the process was divided into three stages. In stage I, Ankara fibre was pulped through open hot digestion. In stage II, the pulp was subjected to bio-bleaching in two experimental setups: Set I (without sucrose) and Set II (with sucrose) for 5 days. In stage III, chemical bleaching was used to improve the final brightness of the treated pulps. A novel comparison was made between the bio-bleaching efficiency of an individual isolate g5 (BI) and a bacterial consortium (BC). This research highlighted that bio-bleaching with the consortium effectively removed lignin (140±60 mg/l) and colour (1830±50 PCU), especially in the presence of sucrose, compared to using a single xylanase isolate. Pulp residue/filtrate collected at each stage was estimated based on parameters such as colour and lignin content. After stage III (chemical bleaching), the release of colour and lignin in pulp filtrate was higher in BI compared to BC, indicating the consortium's effectiveness during bio-bleaching, which leaves fewer degradable lignin structures for the chemical bleaching stage. Papers crafted from consortium-treated pulp also exhibited higher brightness than those treated with the isolate. This study reveals the synergistic effect of microbial consortia, leading to more efficient lignin degradation and enhanced bio-bleaching capabilities, supporting the development of greener industrial processes. Ultimately, this study demonstrates a unique and eco-friendly approach to papermaking, combining C. procera and enzymatic bio-bleaching to reduce dependency on hazardous chemicals and support sustainable industry practices.

Water Hyacinth Plant Fibre Characterization

This work is on the specie of the water hyacinth (WH) in the Northern part of Nigeria taken from the lake in Jalingo in the Sahel region of the country. The basic characteristics of the fibres are studied for use in concrete and other allied construction works. They are subjected to physical and chemical tests for the determination of their properties. X-ray diffraction and scanning electron microscopy are applied to study the crystalline phases and mineral oxides, and the morphology and structural characteristics of the WHFs. The TGA/DTA and FTIR methods of analysis are applied to the WHFs to identify and investigate the thermal stability and percentage of weight loss on temperature, and the SEM for the morphology and structural characteristics of the WH fibre. The results show that the presence of peaks on the spectra of the cellulose samples corresponds to bands of microcrystalline cellulose. The WH plant fibre has a moisture content of approximately 13.7 %, density of 666.7 kg/m3, specific gravity of 0.86, and water absorption of 1067 %, and the cellulose, hemicellulose, lignin are 14.1, 21.5, 7.1 %, respectively. The WH fibre has a tensile strength of 0.12 MPa, Young Modulus of 7.7 GPa, elongation of 4.8 %, tensile extension at break of 2.89 mm, and energy at break of 1.04 x 10-3 J. The XRD diffractogram characterization shows that the WH fibre is crystalline in nature, while the FT-IR shows the functional group change of each treatment respectively. The thermal decomposition process of the WH fibre resulted in similar TG and DTG curves due to being lignin cellulosic material. These curves showed a distinct DTG peak (cellulose) and a high-temperature tail (lignin). The morphology of WH fibre shows a well-shaped fibril with a rigid lignin structure coated surface with the capacity to hold the liquid contents with good absorbency. The chemical compound compositions of the WH fibre contains Ca, K, Cl, C, Al, Si, Fe, S, Y, Ti, P, Mg, Na, and N.

Study on the Relationship between the Structure and Pyrolysis Characteristics of Lignin Isolated from Eucalyptus, Pine, and Rice Straw through the Use of Deep Eutectic Solvent.

Understanding the pyrolysis product distributions of deep eutectic solvent (DES)-isolated lignins (DESLs) from different types of biomass is of great significance for lignin valorization. The structure and pyrolysis properties of DESLs obtained from eucalyptus (E-DESL), pine (P-DESL), and rice straw (R-DESL) were studied through the use of various methods such as elemental analysis, GPC, HS-GC, and NMR techniques, and the pyrolysis characteristics and product distributions of the DESLs were also further investigated through the use of TGA, Py-GC/MS, and tubular furnace pyrolysis. DESLs with high purity (88.5-92.7%) can be efficiently separated from biomass while cellulose is retained. E-DESL has a relatively low molecular weight, and P-DESL has a relatively higher hydrogen-carbon effective ratio and a lower number of condensation structures. The Py-GC/MS results show that, during DESL pyrolysis, the monomeric aromatic hydrocarbons, p-hydroxyphenyl-type phenols, and catechol-type phenols are gradually released when the guaiacyl-type phenols and syringyl-type phenols decrease with the rising temperature. 4-methylguaiacol and 4-methylcatechol, derived from the guaiacyl-type structural units, are positively correlated with temperature, which causes a significant increase in products with a side-chain carbon number of 1 from P-DESL pyrolysis. 4-vinylphenol, as a representative product of the R-DESL, derived from p-hydroxyphenyl-type structural units, also gradually increased. In addition, the P-DESL produces more bio-oil during pyrolysis, while gases have the highest distribution in E-DESL pyrolysis. It is of great significance to study the characteristic product distribution of lignin isolated through the use of DES for lignin directional conversion into specific high-value aromatic compounds.

Comparison of the Interaction and Structure of Lignin in Pure Systems and in Asphalt Media by Molecular Dynamics Simulations.

Lignin is a class of organic aromatic polymers contributing to the rigidity and strength of plants and has been proposed as a modifier to improve asphalt performance on road pavement. However, contradicting experimental results on the lignin miscibility in asphalt were found from different studies, and lignin has been found to self-assemble in different solutions. Thus, investigating the interaction and microstructure of lignin in asphalt media in molecular detail is necessary. Molecular dynamics (MD) simulations using both the LAMMPS program with the OPLS-aa force field and the NAMD program with the CHARMM force field have been conducted on pure lignin (including lignin monomer, dimer, and polymer with 17 and 31 units) and their mixtures with model asphalt molecules at different temperatures. Consistent results were observed from both programs and force fields in terms of density, hydrogen bonds, diffusion coefficient, radius of gyration, and radial distribution function. Glass transition was observed in the pure lignin systems based on density and diffusion coefficient calculations at different temperatures. Lignin can form intramolecular hydrogen bonds and intermolecular hydrogen bonds with other lignin and 1,7-dimethylnapthalene in the asphalt mixture, which has dependence on temperature and lignin chain length. Correlating the lignin size and chain length using the power-law relationship showed that lignin polymers in pure systems are in quasi-relaxed structures at different temperatures; lignin molecules stay in quasi-relaxed structures in asphalt mixtures at high temperatures but in collapsed structures at low temperatures. Implementing lignin monomer, dimer, and polymer into the model asphalt mixture can improve its density. Although lignin in different chain lengths aggregates in asphalt, lignin can modify the packing between different components in asphalt media at different temperatures. The work suggests that temperature can significantly influence the miscibility of lignin polymer in asphalt and that lignin can function as both a modifier and a resin in asphalt.

Comparison on thermally modified beech wood in different mediums: Morphology, chemical change and water-related properties

Thermal modification has been proved to be an effective approach to improve the dimensional stability of wood, while different processes of thermal modification often resulted in various efficacy. In this study, the morphology, chemical structure, crystallinity, pore size distribution, and some water-related properties were investigated in order to explore the effect of different mediums (vacuum, nitrogen, steam and air) on thermally modified wood (TMW). It was found that heating medium plays an important role in thermal modification of wood. At both 180 and 210 ℃, the general severity of thermal modification is in the following order: air > steam > nitrogen > vacuum. Accordingly, the highest dimensional stability appeared in air TMW, and then steam, nitrogen, and vacuum. It seemed that the water-related properties were primarily affected by the extent of decomposition of the amorphous polysaccharides, but showed no direct relationship with the pore structure. Lignin changed greatly for TMW treated in steam at 180 ℃ and all TMW treated at 210 ℃, by showing more uniform distribution in all cell wall layers. It might be resulted from the migration of lignin fragments after depolymerization, the formation of pseudo lignin from holocellulose, and the increased relative lignin content in secondary wall. The changes on pore structure and lignin structure might have significant effect on other wood properties.