Wood Lignin Research Articles

Macromolecular Hydrodynamics and Fractal Structures of the Lignins of Fir Wood and Oat Husks.

The topological structure of the macromolecules of lignins isolated from oat husk and fir wood was studied by means of macromolecular hydrodynamic methods. The macromolecular properties were analyzed by evaluating the intrinsic viscosity and coefficients of the translational diffusion and the sedimentation velocity of the lignins in dilute dimethylformamide solutions. The average molecular weights (MDη) and polydispersity parameters were calculated based on the results of the fractionation, as follows: Mw = 14.6 × 103, Mn = 9.0, and Mw/Mn = 1.62 for lignins from fir wood and Mw = 14.9 Mn = 13.5 and Mw/Mn = 1.1 for lignins from oat husks. The fractal analysis of the lignin macromolecules allowed us to identify the distinctive characteristics of the fractal and topological structures of these lignins. The measurements indicated that the fractal dimension (df) values of the guaiacyl-syringyl lignins from oat husks were between 1.71 and 1.85, while the df of a typical guaiacyl lignin from fir wood was ~2.3. Thus, we determined that the lignin macromolecules of oat husks belong to the diffusion-limited aggregation-type cluster-cluster class of fractals of the Meakin-Kolb type, with a predominance of characteristics common to a linear configuration. The lignins of softwood fir trees exhibited a branched topological structure, and they belong to the diffusion-limited aggregation-type particle-cluster class of fractals of the Witten-Sander type. Lignins from oat husks have the linear topology of macromolecules while the macromolecules of the lignins from fir wood can be characterized as highly branched polymers.

Elucidation of bioactivity of tricin released by thioacidolysis from wheat straw lignin

Tricin is a complex compound with chemical bonds to phenylpropane units of lignin in gramineous plants, and it is predominantly bound to lignin by β-O-4 ether bonds. Thioacidolysis cleaves the alkyl aryl ether bonds, which releases tricin from the tricin-lignin complex and maintains the natural structure of the tricin. In this study, milled wood lignin (MWL) was isolated from wheat straw by Bjӧrkman’s method, and the MWL was subjected to thioacidolysis to release tricin from the MWL. Medium-pressure preparative liquid chromatography was used for further purification. FT-IR and 1H-NMR analyses showed that the purified fraction was composed mainly of tricin-type flavonoids. The extracted tricin had strong scavenging capacity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals, with a half maximal inhibitory concentration (IC50) of 51.9 mg/L. Drug sensitivity paper testing showed that the extracted tricin inhibited the growth of Escherichia coli. The bacteriostatic circle diameters of tricin from wheat straw MWL and quercetin standard were 9.17 and 7.52 mm, respectively. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that the tricin from wheat straw MWL had possible inhibitory effect on lung cancer A549 cells, with a maximum inhibitory performance of 44.5%.

Synthesis of 2,6-Dimethoxy-p-aminophenol from Hardwood Lignin.

Although the multiple functional groups in biomass offer notable chances for producing high-value chemicals, most of the current studies focused on the (deep) defunctionalization of biomass and its derivates. Herein, we present a catalytic approach to valorize birch wood lignin with maintaining the methoxy and hydroxy groups in the final product (i. e., 2,6-dimethoxy-p-aminophenol), which has applications in different sectors such as pharmaceuticals. The proved approach involves four steps with a high yield (19.8 wt % on the basis of used lignin) to 2,6-dimethoxy-p-aminophenol. The native lignin in birch wood was first converted using alkaline aerobic oxidation in the presence of copper ions toward high-yield syringaldehyde, which was then selectively oxidized toward 2,6-dimethoxy-1,4-benzoquinone using H2 O2 and V2 O5 . Oximation of 2,6-dimethoxy-1,4-benzoquinone can selectively form 2,6-dimethoxy-1,4-benzoquinone-4-oxime, which can be quantitatively hydrogenated toward 2,6-dimethoxy-p-aminophenol. This work highlights the unique potential of biomass and its derivates for the sustainable production of high-value products with exploring the value of inherent functional groups.

Degradation performance of methylene blue in metal nanoparticle modified 3D mesoporous wood microchannels.

Wood has a rich three-dimensional pore structure and many bottom-up nanochannels. However, the structure of wood itself has limited ability to adsorb dyes, so the effective combination of the unique structure of wood and Pd NPs was studied to achieve efficient degradation of dyes. First, the three-dimensional structure of natural wood is optimized by combining the complex pore structure of wood with Pd NPs to improve the contact process between the dye and Pd NPs. Then, Pd (II) ion can be well reduced to Pd NPs by wood lignin. In addition, Pd NPs can be fixed by hydroxyl groups on cellulose in wood. The flow state inside Pd NPs/wood film and the contact area between catalyst and dye were discussed in detail by hydrodynamic simulation, which filled the gap. It provides reference for composite structure. When Pd NPs/wood membrane was used to treat methylene blue (MB), the degradation efficiency was up to 96.7%, which was 90% higher than that of natural wood. Its TOF value was 1.82 molMBmolPd-1min-1, which was higher than that in the previous literature. Therefore, the novelty of this study is that the mechanism of catalytic degradation of MB by Pd nanoparticles/wood composites is reported for the first time. The internal flow mode and contact condition of the new material are understood, which has a good application prospect.

Improving the Autofluorescence of Lophira alata Woody Cells via the Removal of Extractives.

The autofluorescence phenomenon is an inherent characteristic of lignified cells. However, in the case of Lophira alata (L. alata), the autofluorescence is nearly imperceptible during occasional fluorescence observations. The aim of this study is to investigate the mechanism behind the quenching of lignin's autofluorescence in L. alata by conducting associated experiments. Notably, the autofluorescence image of L. alata observed using optical microscopy appears to be quite indistinct. Abundant extractives are found in the longitudinal parenchyma, fibers, and vessels of L. alata. Remarkably, when subjected to a benzene-alcohol extraction treatment, the autofluorescence of L. alata becomes progressively enhanced under a fluorescence microscope. Additionally, UV-Vis absorption spectra demonstrate that the extractives derived from L. alata exhibit strong light absorption within the wavelength range of 200-500 nm. This suggests that the abundant extractives in L. alata are probably responsible for the autofluorescence quenching observed in the cell walls. Moreover, the presence and quantity of these extractives have a significant impact on the fluorescence intensity of lignin in wood, resulting in a significant decrease therein. In future studies, it would be interesting to explore the role of complex compounds such as polyphenols or terpenoids, which are present in the abundant extractives, in interfering with the fluorescence quenching of lignin in L. alata.

Superflexible Artificial Soft Wood.

Soft woods have attracted enormous interest due to their anisotropic cellular microstructure and unique flexibility. The conventional wood-like materials are usually subject to the conflict between the superflexibility and robustness. Inspired by the synergistic compositions of soft suberin and rigid lignin of cork wood which has good flexibility and mechanical robustness, an artificial soft wood is reported by freeze-casting the soft-in-rigid (rubber-in-resin) emulsions, where the carboxy nitrile rubber confers softness and rigid melamine resin provides stiffness. The subsequent thermal curing induces micro-scale phase inversion and leads to a continuous soft phase strengthened by interspersed rigid ingredients. The unique configuration ensures crack resistance, structural robustness and superb flexibility, including wide-angle bending, twisting, and stretching abilities in various directions, as well as excellent fatigue resistance and high strength, overwhelming the natural soft wood and most wood-inspired materials. This superflexible artificial soft wood represents a promising substrate for bending-insensitive stress sensors.

Physicochemical Properties of Soda and Kraft Lignin Extracted from Gmelina arborea Wood

Lignin, an amorphous biopolymer is one of the major components of wood. In this study, lignin was extracted from Gmelina arborea wood using Soda and Kraft pulping processes. The lignin was characterized using Fourier Transformed Infrared Spectrometer (FTIR), UV/visible spectrometer, electrospray ionization mass spectrometer and scanning electron microscope (SEM). Results revealed that G. arborea wood lignins contained several chemical functional groups. Kraft lignin (KL) contain carboxyl and thiol group in addition to other functional groups such as methoxyl, alcohols and phenolic. UV/ visible spectroscopy results revealed that Soda lignin (SL) absorbed at higher wavelength than Kraft lignin. The concentrations of both conjugated and non-conjugated phenolic group were higher in Kraft lignin than Soda lignin. ESI-MS spectra revealed that the composition of the monomers was higher in Kraft lignin while dimers composition was higher in Soda lignin. The surface morphology of both lignins were heterogeneous with uneven particle size. These physicochemical properties of lignin will enhance their applications as adsorbents, corrosion inhibitors and in the production of some industrial chemical intermediates.

Fabrication of environmentally, high-strength, fire-retardant biocomposites from small-diameter wood lignin in situ reinforced cellulose matrix

Fabrication of environmentally, high-strength, fire-retardant biocomposites from small-diameter wood lignin in situ reinforced cellulose matrix

Mechanism of enhanced enzymatic hydrolysis performance by ethanol assisted deep eutectic solvent pretreatment- from the perspective of lignin

Valorization of lignocellulose has received a lot of attention due to the abundance of lignocellulosics. It was showed that synergistic carbohydrate conversion and delignification could be achieved via ethanol assisted DES (choline chloride/lactic acid) pretreatment. To explore the reaction mechanism of lignin in the DES, milled wood lignin obtained from Broussonetia papyrifera was subjected to pretreatment at critical temperatures. The results suggested that ethanol assistance could contribute the incorporation of ethyl groups and reduce condensation structures of Hibbert’s ketone. Adding ethanol at 150 °C not only decreased formation of condensed G unit (from 7.23% to 0.87%), but also removed J and S’ substructures, thus effectively reducing the adsorption of lignin on cellulase, and promoting the glucose yield after enzymatic hydrolysis.

Effect of sulfuric acid/ethanol treatment on yellow poplar milled wood lignin

Effect of sulfuric acid/ethanol treatment on yellow poplar milled wood lignin

Effect of sulfuric acid/ethanol treatment on yellow poplar milled wood lignin

Effect of sulfuric acid/ethanol treatment on yellow poplar milled wood lignin

Single-step conversion of wood lignin into phenolic amines

•Woody lignin is directly converted into aromatic amines •Lignin is selectively removed while (hemi)cellulose is kept intact •The process does not compromise the further processing property of (hemi)cellulose •The aromatic amines have the potential to be upgraded into useful fine chemicals Although the transformation of lignin monomers and model compounds into nitrogenated chemicals has been actively investigated, the production of organonitrogen chemicals directly from lignin has been scarcely reported. Here, we communicate a single-step catalytic strategy for producing phenolic amines directly from wood lignin via reductive fractionation in an aqueous ammonia-alcohol mixture over Ru catalyst. Depending on the type of alcohol used, primary, secondary, and ternary phenolic amines can all be synthesized and reach a maximum yield of 26.6%. During the process, native lignin was selectively removed from woody biomass, leaving other constituents, especially (hemi)cellulose, largely unaffected. The obtained phenolic amines were further upgraded into products with enhanced functions. This work exemplifies the possibility for the production of N-functional compounds from lignin, expanding the options for the lignin-first strategy in biomass refinery. Although the transformation of lignin monomers and model compounds into nitrogenated chemicals has been actively investigated, the production of organonitrogen chemicals directly from lignin has been scarcely reported. Here, we communicate a single-step catalytic strategy for producing phenolic amines directly from wood lignin via reductive fractionation in an aqueous ammonia-alcohol mixture over Ru catalyst. Depending on the type of alcohol used, primary, secondary, and ternary phenolic amines can all be synthesized and reach a maximum yield of 26.6%. During the process, native lignin was selectively removed from woody biomass, leaving other constituents, especially (hemi)cellulose, largely unaffected. The obtained phenolic amines were further upgraded into products with enhanced functions. This work exemplifies the possibility for the production of N-functional compounds from lignin, expanding the options for the lignin-first strategy in biomass refinery.

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

The structure and properties of lignin can vary depending on the type of lignocellulosic biomass it comes from and the separation techniques used, and also affects its suitability for different applications. In this work, the structure and properties of lignin isolated from moso bamboo, wheat straw, and poplar wood by different treatment processes were compared. Results show that deep eutectic solvent (DES) extracted lignin exhibits well-preserved structures (including β-O-4, β–β, and β-5 linkages), a low molecular weight (Mn = 2300–3200 g/mol), and relatively homogeneous lignin fragments (1.93 < PDI < 2.33) compared to dealkaline lignin (DL) and milled wood lignin (MWL). Besides, lignin samples extracted by DES have a regular nanostructure, higher carbon residue content (>40 %), and excellent antioxidant properties (the free radical scavenging index >20). Among the three types of biomass, the structural destruction of lignin in straw is the most obvious, which is due to the degradation of β-O-4 and β-β linkages during DES treatment. These findings can contribute to a better understanding of the structural changes that occur in various treatment processes from different lignocellulosic biomass, and help maximize the targeted development of their applications based on the characteristics of lignin.

Probing the relationship between chemical structure and thermal degradation behavior of acetone fractionated kraft lignin

This study reports the relationships between structure and thermal degradation behavior of industrial softwood and hardwood kraft lignin (KL) after acetone fractionation to obtain acetone soluble (AS) and acetone insoluble (AI) fractions with reduced structural polydispersity. The structure and thermal degradation behavior of AS-KL and AI-KL was examined by gel permeation chromatography, Fourier transform infrared, quantitative carbon-13 nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. The results showed that the AS-KL fractions had reduced apparent molecular weight, lower polydispersity, less native wood lignin side chains, greater aromatic hydroxyl groups, and more condensed structures. In contrast, the AI-KL fractions showed substantially larger apparent molecular weight and polydispersity, as well as more aliphatic hydroxyl groups and native lignin side chains. Consequently, AI-KL samples exhibited greater thermal degradation activation energy than those of AS-KL samples because the former fractions had a larger apparent molecular weight as well as more aliphatic OH groups, which facilitated hydrogen bonding between lignin polymers, improving their thermal stability. This finding suggests that acetone fractionation of KL can be used to examine the relationship between structure and thermal degradation of industrial KL. These results also provide important information on the thermal degradation behavior of acetone fractionated products with relevant chemical and physical properties for a specific application, such as raw materials for lignin valorization.

Effect of thermo-vacuum modification on selected chemical, physical, and mechanical properties of Siberian larch (Larix sibirica L.) wood

ABSTRACT The primary aim of this research was to investigate and evaluate the effects of thermo-vacuum modification through forced convection on selected chemical, physical, and mechanical characteristics of Siberian larch (Larix sibirica L.) wood. Larch wood boards were thermally-modified, using press-vacuum plant technology, for three hours at a temperature of 200 °C and a pressure of 350 mBar. In order to characterise the thermally-modified (TH) and unmodified (CTRL) wood samples, the extractives, lignin and holocellulose content, volumetric swellings, compression strength, and modulus of elasticity (MOE) were determined. Gas chromatographic-mass spectrometric (GC-MS) analysis revealed chemical compound changes as a result of the thermal modification process where some extractives became undetectable after treatment while some new extractives were detected. Thermally-modified larch wood exhibited lower volumetric swelling compared to the untreated samples. Markedly, thermally-modified larch wood had lower tendency to absorb moisture. In addition, thermally-treated wood had slightly higher compression strength parallel to the grain, which was 0.29% higher than that of unmodified samples. Meanwhile, a 7.6% reduction in MOE was recorded in the thermally-treated wood.

Unveiling lignin structures and lignin-carbohydrate complex (LCC) linkages of bamboo (Phyllostachys pubescens) fibers and parenchyma cells

Bamboo (Phyllostachys pubescens) is an attractive biomass block to develop biorefining industry, however, less emphasis has been placed on elucidating the chemical linkage variations of lignin and LCC between different bamboo cell walls. Here, purified milled wood lignin (MWLp) and lignin-carbohydrate complex (LCC) were isolated from bamboo (Phyllostachys pubescens) fibers (BF) and parenchyma cells (PC), respectively. The variations of structure features and chemical linkages of lignin and LCC were investigated via FT-IR, 2D HSQC NMR, and 31P NMR techniques. 2D HSQC NMR revealed that β-O-4 alkyl-aryl ether linkages and resinol (β-β) substructure were the main substructures in BF-MWLp and PC-MWLp. β-1 linkages existed in the PC-MWLp (3.18/100 Ar), but not in BF-MWLp. Moreover, tricin, as a flavonoid compound, was only detected in the BF-MWLp. The amount of the syringyl (S) units of PC-MWLp was higher than BF-MWLp. The results indicated that phenyl glycoside (PhGlc) bonds (mainly lignin and xylan) were the predominant chemical linkage type of LCC bonds in BF-LCC and PC-LCC, and the high contents of PhGlc bonds (45.53/100 Ar) were presented in PC. Our finding can provide a reference for the structural variations of lignin and LCC between the different bamboo cell walls.

Fungal Selectivity and Biodegradation Effects by White and Brown Rot Fungi for Wood Biomass Pretreatment.

The biodegradation path and mechanism of wood varies depending on diverse fungi and tree species, as fungi possess selectivity in degradation of versatile wood components. This paper aims to clarify the actual and precise selectivity of white and brown rot fungi and the biodegradation effects on different tree species. Softwood (Pinus yunnanensis and Cunninghamia lanceolata) and hardwood (Populus yunnanensis and Hevea brasiliensis) were subjected to a biopretreating process by white rot fungus Trametes versicolor, and brown rot fungi Gloeophyllum trabeum and Rhodonia placenta with various conversion periods. The results showed that the white rot fungus Trametes versicolor had a selective biodegradation in softwood, which preferentially convert wood hemicellulose and lignin, but cellulose was retained selectively. Conversely, Trametes versicolor achieved simultaneous conversion of cellulose, hemicellulose and lignin in hardwood. Both brown rot fungi species preferentially converted carbohydrates, but R. placenta had a selectivity for the conversion of cellulose. In addition, morphological observation showed that the microstructures within wood changed significantly, and the enlarged pores and the improved accessibility could be beneficial for the penetration and accessibility of treating substrates. The research outcomes could serve as fundamental knowhows and offer potentials for effective bioenergy production and bioengineering of bioresources, and provide a reference for further application of fungal biotechnology.

Preparation and Anti-Lung Cancer Activity Analysis of Guaiacyl-Type Dehydrogenation Polymer.

In this paper, guaiacyl dehydrogenated lignin polymer (G-DHP) was synthesized using coniferin as a substrate in the presence of β-glucosidase and laccase. Carbon-13 nuclear magnetic resonance (13C-NMR) determination revealed that the structure of G-DHP was relatively similar to that of ginkgo milled wood lignin (MWL), with both containing β-O-4, β-5, β-1, β-β, and 5-5 substructures. G-DHP fractions with different molecular weights were obtained by classification with different polar solvents. The bioactivity assay indicated that the ether-soluble fraction (DC2) showed the strongest inhibition of A549 lung cancer cells, with an IC50 of 181.46 ± 28.01 μg/mL. The DC2 fraction was further purified using medium-pressure liquid chromatography. Anti-cancer analysis revealed that the D4 and D5 compounds from DC2 had better anti-tumor activity, with IC50 values of 61.54 ± 17.10 μg/mL and 28.61 ± 8.52 μg/mL, respectively. Heating electrospray ionization tandem mass spectrometry (HESI-MS) results showed that both the D4 and D5 were β-5-linked dimers of coniferyl aldehyde, and the 13C-NMR and 1H-NMR analyses confirmed the structure of the D5. Together, these results indicate that the presence of an aldehyde group on the side chain of the phenylpropane unit of G-DHP enhances its anticancer activity.

Structural comparison of different isolated eucalyptus lignins and analysis of their interaction mechanism with bovine serum albumin solution under QCM-D

Abstract In this study, representative lignin samples differing in hydroxyl content, molecular weight, linkage composition and lignin units ratio were prepared from eucalyptus wood by different isolation means and modification means: milled wood lignin (MWL), kraft lignin classified at different pH (KL), lignocresol (LC), lignoresorcinol (LR), lignopyrogallol (LP) as well as lignocresol secondary functional switched samples (LC 2ndderiv). The structure of various lignins was characterized in detail by Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). In order to eliminate the interference of other factors, bovine serum albumin (BSA) with relatively simple protein structure and different kinds of lignin and their derivatives were selected as the research objects. The adsorption/desorption behavior and mechanism between lignin samples and BSA were studied by quartz crystal microbalance with dissipation monitoring (QCM-D). The results showed that the content of phenolic hydroxyl was the main factor affecting the interaction of lignin and BSA, but in addition, the molecular size, linkages composition and the types of lignin units also had important effects on its adsorption behavior. The research will provide theoretical guidance and all-round reliable basic data for the interaction of lignin on lignocellulose hydrolysis enzymes in industrial application.

Development of a phosphorous-based biorefinery process for producing lignocellulosic functional materials from coconut wastes

This work aimed to develop a phosphorous-based biorefinery process for obtaining phosphorylated lignocellulosic fractions in a one-pot protocol from coconut fiber. Natural coconut fiber (NCF) was mixed with 85 % m/m H3PO4 at 70 °C for 1 h to yield the modified coconut fiber (MCF), aqueous phase (AP), and coconut fiber lignin (CFL). MCF was characterized by its TAPPI, FTIR, SEM, EDX, TGA, WCA, and P content. AP was characterized regarding its pH, conductivity, glucose, furfural, HMF, total sugars and ASL contents. CFL structure was evaluated by FTIR, 1H, 31P and 1H-13C HSQC NMR, TGA and P content and was compared to that of milled wood lignin (MWL). It was observed that MCF and CFL were phosphorylated during the pulping (0.54 and 0.23 % wt., respectively), while AP has shown high sugar levels, low inhibitor content, and some remaining phosphorous. The phosphorylation of MCF and CFL also showed an enhancement of their thermal and thermo-oxidative properties. The results show that a platform of functional materials such as biosorbents, biofuels, flame retardants, and biocomposites can be created through an eco-friendly, simple, fast, and novel biorefinery process.