Milled Wood Lignin Research Articles

SUGARCANE BAGASSE LIGNIN OBTAINED BY DIFFERENT EXTRACTION METHODS

Sugarcane bagasse (SB) is a by-product of ethanol production obtained in large quantities worldwide, including Brazil. Lignin is one of SB components, and its extraction is of great interest due to its vast potential for use. In this study, sugarcane bagasse was subjected to two methods of lignin extraction to obtain: Klason lignin (LKL) and milled wood lignin (MWL). The syringil/guaiacyl ratio of the lignin obtained from sugarcane bagasse was 1.67. Thermogravimetric analysis showed that LKL is more resistant to thermal degradation than MWL. According to the FTIR spectra, LKL yields a more oxidized lignin, presenting greater changes in its structure than MWL. Thus, this study provides information on the changes caused by different extractions and strengthens future studies on the transformation of lignin into products of high added value.

Structural Changes in Milled Wood Lignin (MWL) of Chinese Quince (Chaenomeles sinensis) Fruit Subjected to Subcritical Water Treatment.

Subcritical water treatment has received considerable attention due to its cost effectiveness and environmentally friendly properties. In this investigation, Chinese quince fruits were submitted to subcritical water treatment (130, 150, and 170 °C), and the influence of treatments on the structure of milled wood lignin (MWL) was evaluated. Structural properties of these lignin samples (UL, L130, L150, and L170) were investigated by high-performance anion exchange chromatography (HPAEC), FT-IR, gel permeation chromatography (GPC), TGA, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 2D-Heteronculear Single Quantum Coherence (HSQC) -NMR, and 31P-NMR. The carbohydrate analysis showed that xylose in the samples increased significantly with higher temperature, and according to molecular weight and thermal analysis, the MWLs of the pretreated residues have higher thermal stability with increased molecular weight. The spectra of 2D-NMR and 31P-NMR demonstrated that the chemical linkages in the MWLs were mainly β-O-4′ ether bonds, β-5′ and β-β′, and the units were principally G- S- H- type with small amounts of ferulic acids; these results are consistent with the results of Py-GC/MS analysis. It is believed that understanding the structural changes in MWL caused by subcritical water treatment will contribute to understanding the mechanism of subcritical water extraction, which in turn will provide a theoretical basis for developing the technology of subcritical water extraction.

An in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged archaeological wood

AbstractThe weakened microstructure of archaeological wood (AW) objects from waterlogged environments necessitates consolidation to avoid anisotropic shrinkage upon drying. Polymer impregnation through submergence or spraying treatments is commonly applied, and for larger and thicker objects, the impregnation period can stretch over decades. Thus, for efficient treatment, continuous monitoring of the impregnation status is required. Today, such monitoring is often destructive and expensive, requiring segments for extraction and chromatographic quantification. This study proposes an in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged AW. A calibration model was built on standards of PEG, cellulose powder, and milled wood lignin using orthogonal partial least squares (OPLS). The OPLS model had a strong linear relationship, and the PEG content in wood of varying degrees of degradation could be determined. However, the accuracy of the model was low with a root mean square error of prediction of 11 wt%. The low accuracy was traced to the heterogeneity in the calibration and validation set samples with regard to the small probing volume of the confocal instrumental setup.

Modification of the aspen lignin structure during integrated fractionation process of autohydrolysis and formic acid delignification

Integrated fractionation process based on autohydrolysis (H) and subsequent formic acid delignification (FAD) has been considered as an effective strategy to separate the main lignocellulosic components in view of the biorefinery. For the better understanding of the structural changes of the lignin during the integrated process, the fractionated aspen lignins were thoroughly characterized by Fourier transform infrared (FT IR), 13C, two-dimensional heteronuclear single quantum coherence (2D-HSQC) and 31P nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Compared to the milled wood lignin (MWL), the fractionated lignins had higher amounts of phenolic OH groups as due to the cleavage of β-O-4 linkages and less alcoholic OH groups mainly due to the esterification of the aliphatic OH groups by formic acid. Demethylation action of the lignin was not significant during the FAD process. More syringyl-propane (S) units were extracted during the H-FAD process than guaiacyl-propane (G) units resulting in a higher S/G ratio and more OCH3 in the fractionated lignins. Furthermore, autohydrolysis of aspen at higher temperature led to more condensation of the fractionated lignins which exhibited higher molecular weight and more β-5 and β-β linkages. The fractionated lignins exhibited high purities due to the breakage of the lignin-carbohydrate bonds.

Vacuum Pyrolysis of Hybrid Poplar Milled Wood Lignin with Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry Analysis of Feedstock and Products for the Elucidation of Reaction Mechanisms

The pyrolysis of lignocellulosic materials is a promising technique to produce fuels and chemicals. It is well known that the most abundant products of lignin pyrolysis are oligomeric molecules, kn...

Formosolv Pretreatment to Fractionate Paulownia Wood Following a Biorefinery Approach: Isolation and Characterization of the Lignin Fraction

Paulownia is a rapid-growth tree with a high biomass production rate per year and low demand of water, which make it very suitable for intercropping systems, as it protects the crops from adverse climatic conditions, benefiting the harvest yields. Moreover, these characteristics make Paulownia a suitable raw material able to be fractionated in an integrated biorefinery scheme to obtain multiple products using a cascade conversion approach. Different delignification pretreatments of biomass have been purposed as a first stage of a lignocellulosic biorefinery. In this study, the formosolv delignification of Paulownia wood was investigated using a second order face-centered factorial design to assess the effects of the independent variables (concentrations of formic and hydrochloric acids and reaction time) on the fractionation of Paulownia wood. The maximum delignification achieved in this study (78.5%) was obtained under following conditions: 60 min, and 95% and 0.05% formic and hydrochloric acid, respectively. In addition, the remained solid phases were analyzed to determine their cellulose content and cooking liquors were also chemically analyzed and characterized. Finally, the recovered lignin by precipitation from formosolv liquor and the pristine lignin (milled wood lignin) in Paulownia wood were characterized and compared by the following techniques FTIR, NMR, high-performance size-exclusion chromatography (HPSEC) and TGA. This complete characterization allowed verifying the capacity of the formosolv process to act on the lignin, causing changes in its structure, which included both phenomena of depolymerization and condensation.

Insight into Depolymerization Mechanism of Bacterial Laccase for Lignin

Laccase is essential for the biodepolymerization of lignin, but the challenge is that the reaction mechanism has not been fully elucidated. The laccase (Lacc) inactivated mutant of Bacillus ligniniphilus L1 had a sharp decline in its ability to degrade lignin, which proved its indispensable role in lignin depolymerization. The purified Lacc from recombinant Escherichia coli BL21 and its mediator system (LMS) displayed significant lignin degradation capacities as well as remarkable thermotolerance and solvent resistance. The chemical oxygen demand removal rates of LMS for alkaline and milled wood lignin have reached 67.0% and 80.9%, respectively. Comprehensive analyses, including Fourier-transform infrared spectrometry, gas chromatography–mass spectrometry, 2D-HSQC-NMR, and time-of-flight secondary ion mass spectrometry, unveiled that Lacc- and LMS-oxidized lignin include at least 10 or more catalytic reactions. Lacc can effectively degrade G-lignin even without a mediator, and the removal rate of G-lignin is higher than that of S-lignin. In addition, the supplementation of the mediator increased the removal rate of H-lignin by Lacc and the cleavage of interunit linkages such as β-O-4, β-5, β-β, 4-O-5, and 5-5. Moreover, we found that Lacc cannot polymerize some aromatic monomers into dimers or polymers, which is different from fungal and plant laccases. It is by far the most detailed study describing the reaction mechanism of lignin oxidation by bacterial laccase. These results provide new insights into the catalytic mechanism of bacterial laccase and lay the foundation for the application of laccase in lignin valorization.

Structural features and antioxidant behavior of lignins successively extracted from ginkgo shells (Ginkgo biloba L)

Ginkgo shells as by-products from Ginkgo biloba L. industries with a remarkable annual output up to now are not fully analyzed and exploited. For the application of ginkgo shells beyond their current roles, structure and antioxidant activity of milled wood lignins successively extracted from two ginkgo shell species were investigated. Results showed lignin in ginkgo shells is abundant in guaiacyl units with the presence of ferulates and p-coumarates and demonstrates a high yield of vanillin (1.47–1.65 mmol/g-lignin) by nitrobenzene oxidation, much higher than general softwoods and hardwoods (0.6–0.9 mmol/g-lignin), which makes ginkgo shells good feedstocks for the production of food and beverage flavoring agent. By increasing the extent of ball-milling (4–8 h), the polydispersity of lignin molecular weight exhibits negligible change, but condensation and aldol interconversion occur to its Cβ/C5 structure and end-groups, respectively. Lignin in ginkgo shells also features outstanding antioxidant activity with the optimal radical scavenging index of 6.9, much higher than commercial butyl hydroxyanisole (3.85) and butylated hydroxytoluene (0.29), and the phenolic hydroxyl is demonstrated to dominate this contribution by the analysis of statistical product and service solutions. These results reveal lignin in ginkgo shells shows many unique structural and biological properties for materials.

Combining pyrolysis–two-dimensional gas chromatography–time-of-flight mass spectrometry with hierarchical cluster analysis for rapid identification of pyrolytic interactions: Case study of co-pyrolysis of PVC and biomass components

Co-pyrolysis of plastic/lignocellulosic biomass mixtures produces an extremely complex assortment of pyrolyzates. In the present work, co-pyrolysis of PVC with cellulose or xylan or milled wood lignin was conducted by employing pyrolysis–two-dimensional gas chromatography–time-of-flight mass spectrometry (Py-GC × GC-TOFMS) with the aim of achieving high throughput and comprehensive analysis of the complex pyrolyzates. Then, hierarchical cluster analysis (HCA), which is an algorithm that groups similar objects into groups called clusters, was applied to accomplish rapid screening for compounds influenced by pyrolytic interactions. This combined approach improved compound separation and identifiability and allowed the subsequent easy identification of new compounds and compounds increased or decreased by pyrolytic interactions during co-pyrolysis. The change in distribution during co-pyrolysis clearly suggests the occurrence of HCl-catalyzed dehydration of anhydrosugars and conversion of methoxyphenols into phenolic compounds. Thus, this study reveals the effectiveness of the approach combining Py-GC × GC-TOFMS with HCA, which promises to contribute to the acceleration of research on pyrolytic interactions. The understanding of pyrolytic interactions gained thereby will be crucial for maximizing the yield and quality of desired chemicals and fuels from plastic/lignocellulosic biomass.

Effects of Hot Water Pre-Extraction on Energy Consumption and Brightness of Bamboo Alkaline Peroxide Mechanical Pulp

The main purpose of this paper was to investigate the effects of hot water pre-extraction (HWP) on the refining energy consumption and the brightness of bamboo alkaline peroxide mechanical pulp (APMP). It was found that compared with un-extraction, the refining energy consumption dropped by about one-third after HWP. The reduction of energy consumption was proved through enhancing the channel of water and chemicals into inferior fiber based on the surface characterization of bamboo. Scanning electron microscope (SEM) images showed that the HWP made the fibers' structure loose and porous. Both pore volume and specific surface area were increased significantly after HWP, by 260.00% and 1804.76%, respectively. A decrease in pulp brightness was mainly due to the formation of new chromophore groups during the HWP process. The results of 13C nuclear magnetic resonance spectroscopy (13C-NMR) illustrated that some structures of milled wood lignin (MWL), such as guaiacyl, etherificated guaiacyl, and aromatic units, were increased during the HWP process. However, some lignin-links units of α-O-4, β-O-4, and some carbohydrate structures such as xylan, α- and β-glucose, and β-and β-mannose in lignin-carbohydrate complex (LCC) were evidently degraded. Additionally, most of the lignin and LCC were degraded under the simulative conditions of HWP bamboo. Furthermore, the analysis of UV spectrophotometry indicated that HWP was conductive to the generation of chromophore groups such as conjugated carbonyl, catechol, and o-benzoquinone.

Pretreatment of willow using the alkaline-catalyzed sulfolane/water solution for high-purity and antioxidative lignin production

In this study, an alkaline-catalyzed sulfolane/water solvent system was developed for isolating high-purity and antioxidative lignin from willow (Salix matsudana cv. Zhuliu). Optimization of the pretreatment conditions such as temperature, sulfolane/water ratio, and alkaline catalyst (NaOH) dosage were comprehensively investigated for effective lignin extraction from willow. The 44.4% of lignin was recovered from the biomass with 54% of delignification in 50/50 (w/w) sulfolane/water system at 170 °C. As the addition of the alkaline catalyst (NaOH) increased to 4%, the delignification yield was increased up to 94% with about 70% of lignin recovery yield. The recovered lignin was comparatively investigated with its control, milled wood lignin (MWL). The β-O-4 linkages and phenolic hydroxyl were well preserved in the extracted lignin fractions with the sulfolane/water system. Furthermore, excellent radical scavenging ability was observed with the extracted lignins by sulfolane/water pretreatments owing to rich phenolic hydroxyl groups in the lignins. Hence, systematical investigation on the lignin properties and potential applications under sulfolane organosolv pretreatment would promote the utilization of lignin in biorefinery processes.

Effect of lignin on the self-bonding of a natural fiber material in a hydrothermal environment: Lignin structure and characterization

Self-bonding natural fiber materials (SNFMs) were prepared at different initial moisture contents (IMCs) through a molding pressing process. The self-bonding mechanism of the SNFMs was deduced from the chemical and structural changes of lignin and their mechanical strengths. The structural transformations of milled wood lignin (MWL) in the SNFMs were investigated by two-dimensional heteronuclear single quantum coherence, quantitative 31P-nuclear magnetic resonance spectra, gelpermeation chromatography, and thermogravimetric analysis. As IMC increased from 0% to 80%, the tensile strength increased from 23.0 to 70.0 MPa and the density increased from 0.99 to 1.05 g/cm3. IMC affected the distribution and abundance of the typical lignin linkages (β-O-4′, β-β, and β-5′) and the S–OH/G–OH ratios of lignin. Moreover, as IMC increased, the aliphatic hydroxyl groups proportionally decreased, while the condensed phenolic and non-condensed phenolic hydroxyl groups increased, the molecular weight of MWL became larger, and the thermal stability of lignin improved. These findings indicate the simultaneous occurrence of depolymerization and condensation reactions of lignin. The condensation reaction dominated, improving the mechanical strength of the material. Our results explain (at least partly) the self-bonding mechanism of SNFMs.

High Purity and Low Molecular Weight Lignin Nano-Particles Extracted from Acid-Assisted MIBK Pretreatment.

A simple and economical biorefinery method, organosolv methyl isobutyl ketone (MIBK) pretreatment assisted by Lewis acid ferric trichloride hydrolysis, was proposed for fractionating the lignin from extractive-free Eucalyptus powder at the nanoscale, accompanied by another product furfural, derived from hemicellulose. Under the conditions (180 °C, 1 h) optimized based on the best yield of furfural, 40.13% of the acid-insoluble lignin (AIL) could be obtained with a high purity of 100%, a low molecular weight of 767 (Mn) and improved thermostability. The extracted lignin was characterized by its chemical structure, thermostability, homogeneity, molecular weight, and morphology as compared with milled wood lignin (MWL). The results showed significant variations in chemical structures of the extracted lignin during the pretreatment. Specifically, the aryl ether linkage and phenylcoumarans were broken severely while the resinols were more resistant. The G-type lignin was more sensitive to degradation than the S-type, and after the pretreatment, H-type lignin was formed, indicating the occurrence of a demethoxylation reaction at high temperature. Moreover, the lignin nano-particles were identified visually by AFM and TEM images. The dynamic light scattering (DLS) showed that the average diameter of the measured samples was 131.8 nm, with the polydispersity index (PDI) of 0.149. The MIBK-lignin nano-particles prepared in our laboratory exhibit high potentials in producing high functional and valuable materials for the application in wide fields.

Effluent of biomass cooking with active oxygen and solid alkali (CAOSA): component separation, recovery and characterization.

Effluent from biomass pretreatment industries affects a substantial proportion of industrial wastewater and can be troublesome to treat. In a new environmentally benign biomass pretreatment approach based on cooking with active oxygen and solid alkali (CAOSA), some precipitates were found to be produced while the effluent (yellow liquor) was treated with alcohol or acid. Based on the precipitation approaches, component contents in CAOSA yellow liquor were successfully made clear, consisting of 57.19 wt% low molecular weight acid salts, 15.47 wt% lignin, 4.30 wt% saccharides and 23.04 wt% inorganic salts. Different organic solvents were tested as the precipitants, and when ethanol was used, over 81 wt% of the compounds in the yellow liquor could be precipitated. Meanwhile, 89.2% of the solid alkali consumed in CAOSA pretreatment could be recovered, showing prospects for primary effluent treatment. Furthermore, CAOSA lignin (CL) was recovered by acid precipitation from yellow liquor. By characterization, CL was found to have lower molecular weight and higher β-O-4 bond (60.05%) ratio than milled wood lignin (MWL, 48.64%), and thus, it might be a more ideal feedstock for further valorization.

Spruce milled wood lignin: linear, branched or cross-linked?

Plausible up-to-date structural model of spruce MWL in agreement with the current structural and molecular weight data.

Correction: Spruce milled wood lignin: linear, branched or cross-linked?

Correction for ‘Spruce milled wood lignin: linear, branched or cross-linked?’ by Mikhail Balakshin et al., Green Chem., 2020, 22, 3985–4001, DOI: 10.1039/D0GC00926A.

Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob.

Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives.

Impacts of Pyrolytic Interactions during the Co-pyrolysis of Biomass/Plastic: Synergies in Lignocellulose-Polyethylene System

Multiple pyrolytic interactions in the cellulose-hemicellulose-lignin-polyethylene system were thoroughly investigated using a novel approach, which evaluates the pyrolytic interaction impacts through product recovery tests and the in-situ pyrolysate monitoring by evolved gas analysis-mass spectrometry. Fast pyrolysis of neat cellulose, xylan, milled wood lignin, beech wood, polyethylene, and their mixtures was conducted at 650 °C using the combined approach. Interactions in the cellulose/polyethylene, xylan/polyethylene, and milled wood lignin/polyethylene systems enhanced the production of CO and C2-C3 hydrocarbons, and simultaneously inhibited that of solids such as heavy tar, wax, and coke. Polyethylene worked as a dispersant of biomass upon injection, and the improved gasification was mainly due to the enhanced hydrogen-exchange between hydrogen-rich polyethylene pyrolysates and carbon-centered radicals in vapor phase. The results suggested that pyrolytic interactions in the biomass components (cellulose-hemicellulose-lignin) occur preferentially before contact with polyethylene, and then the beech wood pyrolysates further interact with the polyethylene pyrolysates. Thus, this novel approach allowed advanced evaluation of pyrolytic interactions and can be applied to different combinations and compositions in the cellulose-hemicellulose-lignin-plastic system. It will help understand the nature of co-pyrolysis systems and predict the significance of co-pyrolysis in practical energy and chemical feedstock production.

How Pseudo-lignin Is Generated during Dilute Sulfuric Acid Pretreatment.

Pseudo-lignin is generated from lignocellulose biomass during pretreatment with dilute sulfuric acid and has a significant inhibitory effect on cellulase. However, the mechanism of pseudo-lignin generation remains unclear. The following main points have been addressed to help elucidate the pseudo-lignin generation pathway. Cellulose and xylan were pretreated with sulfuric acid at different concentrations; aliquots were periodically collected; and the changes in the byproducts of the prehydrolysate were quantified. Milled wood lignin (MWL) mixed with cellulose and xylan was pretreated to evaluate the impact of lignin on pseudo-lignin generation. Furfural, 5-hydroxymethylfurfural, and MWL were pretreated as model compounds to investigate pseudo-lignin generation. The result indicated that the increasing acid concentration significantly promoted the generation of pseudo-lignin. When the acid concentration was increased from 0 to 1.00 wt %, pseudo-lignin was increased from 1.36 to 4.05 g. In addition, lignin promoted the pseudo-lignin generation through the condensation between lignin and the generated intermediates.

Enhancing isolation of p-coumaric and ferulic acids from sugarcane bagasse by sequential hydrolysis

To improve the yield of p-coumaric acid (p-CA) and ferulic acid (FA), sequential alkaline and acid hydrolysis was applied to sugarcane bagasse. Gas chromatography-mass spectrometry was used to quantify p-CA and FA. The sequential hydrolysis isolated more p-CA and FA from sugarcane bagasse than did alkaline hydrolysis or acid hydrolysis alone. Ethyl acetate extracted more p-CA and FA than chloroform. Increased temperature improved the yield of p-CA and FA. The total yields of p-CA and FA from sugarcane bagasse were 4.38 and 0.79%, respectively. For p-CA, the ester and ether bonds accounted for 93.60% and 6.40% of the total linkages, respectively. For FA, the ester and ether bonds accounted for 51.90% and 48.10% of the total linkages, respectively. Cleavage of the bond between hydroxycinnamic acid (p-CA and FA) and lignin was also confirmed by 13C NMR through comparison with the spectra of milled wood lignin and alkaline-soluble lignin.