Lignin Structure Research Articles

Maleic acid modified lignin for preparation of ultra-flexible and UV shielding gelatin/lignin films

Alkaline lignin and sodium lignosulfonate were chemically modified by using maleic acid for potential application on the production of ultra-flexible gelatin films. The comparison results in morphology and chemical structures of the two types of lignin before and after modification revealed that carboxyl and CC groups were successfully grafted onto the lignin, resulting in the changes in physical-chemical properties. Compared to modified sodium lignosulfonate, modified alkaline lignin (MAL) was much more appropriate in the preparation of gelatin (GEL)/lignin films by endowing the films with transparency and excellent UV light shielding ability. Elongation at break of GEL/MAL films were more than two times that of the pure gelatin film, which greatly addressed the brittleness issues of the pure gelatin films during use, indicating that the modified alkaline lignin could be used as renewable additive with replacement of glycerol. The results in this study also gave evidence that the sources and structure of lignin affect its compatibility with gelatin solution. The higher weight loss rate and lower pyrolysis degradation temperature indicated that the gelatin/lignin films were much more easily thermal degradable at the end of service life. This research provided a potential and efficient approach on the production of renewable and biological films from gelatin and lignin.

Photocatalytic efficient cleavage of C-C bond in lignin model using water as solvent

Photocatalytic lignin C-C bond (LCCD) cleavage is one possible strategy to promote high-value utilization of lignin. However, it still confronts many difficulties due to the stability of the lignin structure and the high activation energy of LCCD. Herein, a graphitic carbon nitride photocatalyst with the introduction of cyano groups and K+ ions (6MCN) is synthesized. Compared with pure carbon nitride (PCN), 6MCN exhibits superior photogenerated carrier separation ability, excellent sunlight capture ability, and greater oxidation capability. Under simulated sunlight, 6MCN significantly improves the photocatalytic efficiency of LCCD breakage in β-1 lignin models and aromatic vicinal diols (ACD), compared with earlier literature. The improved Cβ radical mechanism and single-electron transfer (SET) pathway are the primary mechanisms in the photocatalytic reaction. Hydroxyl radicals, superoxide radicals, and photogenerated holes are all involved in the photocatalytic cleavage of LCCD. However, hydroxyl radicals, as the most important active radicals, not only trigger the SET mechanism and Cβ radical mechanism but also provide the O and H atoms required for photocatalytic fracture of LCCD, which is very critical to obtain excellent photocatalytic efficiency. This work offers new insights into the photocatalytic breakage of LCCD in β-1 lignin models and ACD through the development of high-performance photocatalysts and the control of radical types.

Photothermal Properties and Solar Water Evaporation Performance of Lignin-Based Polyurethane Foam Composites.

Solar interfacial evaporation is the most promising route for desalination because it is highly efficient, affordable and offers green energy. Polyurethane foam (PUF) is an ideal substrate material for efficient solar water evaporation because of its low thermal conductivity, affordability, and high efficiency for continuous water transport. However, PUF exhibits poor mechanical properties after water absorption and expansion, and lacks the photothermal conversion effect. In this study, biorefinery lignin with efficient photothermal properties was introduced to prepare functional lignin-based PUF (LPUF), and the relationship between the molecular structure of fractioned lignin and the solar water evaporation performance was systematically investigated. The addition of lignin effectively enhanced the mechanical properties of LPUF after water absorption and swelling, and imparted the foam with a photothermal conversion effect. The water evaporation rate of LPUF was as high as 2.58 kg m-2 h-1 and could be further improved to more than 3.0 kg m-2 h-1 after loading polyaniline (PANI) on the surface of LPUF. LPUF-PANI exerted an excellent purification effect on dye wastewater with outstanding long-term stability, providing a potential solution for ecofriendly and sustainable economic production of fresh water. This study broadens the effective utilization of LPUF bulk materials in the fields of energy and environment.

Holistic investigation of structural evolution in corn stover lignin under pretreatment with varying γ-valerolactone concentrations

Until now, research on green and sustainable γ-valerolactone (GVL) pretreatment has predominantly centered on component separation efficiency, with limited attention given to the lignin structure. Nonetheless, the lignin's structure is considerably affected by the fractionation, consequently influencing its potential valorization. Herein, we conducted a holistic investigation of the structural evolution of two fractions of lignin in corn stover, obtained under pretreatment with varying GVL concentrations: GVL lignin (GVLL) originated from pretreatment liquor and cellulolytic enzyme lignin (CEL) separated from pretreated residue. Our findings indicated a general positive correlation between the molecular weight and polydispersity index of both GVLL and CEL with the increasing GVL concentration. This phenomenon is attributed to the enhanced lignin dissolution and relocation as the GVL concentration increases. Moreover, higher GVL concentrations also increased the acidity of reaction system, leading to degradation of β-O-4 linkages from 45.2 to 34.9 and 57.6 to 37.9 per 100 aromatic units in GVLL and CEL, respectively. Compared to CEL, GVLL exhibited a more remarkable phenolics yield (33.7% vs. 22.2%) during hydrodeoxygenation due to its superior purity and lower degree of polymerization. Recycling studies demonstrated the stability of GVL at lower concentrations. These findings provide valuable insights for optimizing GVL pretreatment systems.

Lignin-rich extracts as slow-release coating for phosphorus fertilizers

Lignin (L) is the most abundant three-dimensional polymer with versatile yet attractive structural features and chemical properties for applicability as a coating. The properties of lignin are mainly related to its botanical origin, structure and extraction method. Although there has been a lot of interest in using lignin in fertilizing systems, only limited attempts have been dedicated to studying the effect of the lignin structure and origin on the release of P fertilizer. Thus, the aim of this work was to study the effect of lignin polymers, extracted from different plant biomass, as coating materials for P fertilizers. Thus, the effect of the structural features originating from the botanical origin on the properties of coated fertilizers and their slow release were established. To this end, three lignocellulosic biomass, namely olive pomace (OP), barley straw (BS) and wood shavings (WS) were used as feedstock to extract lignin polymers. Those chemical compositions and thermochemical properties were characterized prior to their application as coating for triple super phosphate (TSP) fertilizer. Coated fertilizers were characterized for their morphology and coating thickness prior to their evaluation as slow release P-based fertilizer. A distinct slow P release behavior was reported for lignin-coated fertilizers with TSP@L-OP being the slowest as compared to TSP@L-WS, TSP@L-BS as well as pristine TSP, which confirm that the botanical origin and most likely the chemical structures of lignin has significant impact on the properties of the coating materiel. A 100 % release of P from the uncoated TSP was observed after 3 days, while the released amount ranged from only 16.9 % for TSP@L-OP up to 33.4 % for TSP@L-BS. The impact of these coated fertilizers on nutrients uptake and wheat growth was also scrutinized and an noticeable improvement of wheat shoot biomass was observed with the coated TSP treatments reaching up 57.8 % for TSP@BS, 78.1 % for TSP @WS and 93.7 % for TSP @OP, compared to uncoated TSP. This was concomitant to a slight increase of P concentration in shoots, roots and rhizosphere soil, which confirmed the positive effect of slow release P fertilizers on plant growth.

The white rot basidiomycete Gelatoporia subvermispora produces fatty aldehydes that enable fungal manganese peroxidases to degrade recalcitrant lignin structures.

The ability of some white rot basidiomycetes to remove lignin selectively from wood indicates that low molecular weight oxidants have a role in ligninolysis. These oxidants are likely free radicals generated by fungal peroxidases from compounds in the biodegrading wood. Past work supports a role for manganese peroxidases (MnPs) in the production of ligninolytic oxidants from fungal membrane lipids. However, the fatty acid alkylperoxyl radicals initially formed during this process are not reactive enough to attack the major structures in lignin. Here, we evaluate the hypothesis that the peroxidation of fatty aldehydes might provide a source of more reactive acylperoxyl radicals. We found that Gelatoporia subvermispora produced trans-2-nonenal, trans-2-octenal, and n-hexanal (a likely metabolite of trans-2,4-decadienal) during the incipient decay of aspen wood. Fungal fatty aldehydes supported the in vitro oxidation by MnPs of a nonphenolic lignin model dimer, and also of the monomeric model veratryl alcohol. Experiments with the latter compound showed that the reactions were partially inhibited by oxalate, the chelator that white rot fungi employ to detach Mn3+ from the MnP active site, but nevertheless proceeded at its physiological concentration of 1 mM. The addition of catalase was inhibitory, which suggests that the standard MnP catalytic cycle is involved in the oxidation of aldehydes. MnP oxidized trans-2-nonenal quantitatively to trans-2-nonenoic acid with the consumption of one O2 equivalent. The data suggest that when Mn3+ remains associated with MnP, it can oxidize aldehydes to their acyl radicals, and the latter subsequently add O2 to become ligninolytic acylperoxyl radicals.IMPORTANCEThe biodegradation of lignin by white rot fungi is essential for the natural recycling of plant biomass and has useful applications in lignocellulose bioprocessing. Although fungal peroxidases have a key role in ligninolysis, past work indicates that biodegradation is initiated by smaller, as yet unidentified oxidants that can infiltrate the substrate. Here, we present evidence that the peroxidase-catalyzed oxidation of naturally occurring fungal aldehydes may provide a source of ligninolytic free radical oxidants.

Solubilization and structural changes of lignin in naked oat stems during subcritical water autohydrolysis

In this study, the solubilization and structural changes of lignin in naked oat stems were investigated under subcritical water autohydrolysis systems (170–210 °C, 0.68–1.85 MPa). In this system, Hemicellulose was preferentially hydrolyzed in the liquid water at elevated temperatures, leading to the production of acetic acid and glucuronic acid, which acidified the reaction system. Under acidic and high-temperature conditions, lignin primarily underwent degradation and condensation reactions. At autohydrolysis temperatures below 190 °C and autohydrolysis pressures below 1.22 MPa, lignin degradation was predominant, realizing a maximum lignin removal of 47.8 % and breakage of numerous β-O-4 bonds from lignin. At autohydrolysis temperatures above 190 °C and autohydrolysis pressures above 1.22 MPa, lignin condensation dominated, with an increase in the amount of organic acids generated upon hemicellulose degradation, leading to condensation reactions with the degraded low-molecular-weight lignin. The degree of lignin condensation was positively correlated with the temperature of the reaction system. This study provides essential insights into the dynamic changes in the structure of lignin in both the hydrolysis residue and hydrolysis solution during subcritical water autohydrolysis.

Revealing the structural changes of lignin in Chinese quince (Chaenomeles sinensis) fruit as it matures

Chinese quince fruits (Chaenomeles sinensis) contain substantial amounts of lignin; however, the exact structure of lignin remains to be investigated. In this study, milled wood lignins (Milled wood lignin (MWL)-1, MWL-2, MWL-3, MWL-4, MWL-5, and MWL-6) were extracted from fruits harvested once a month from May to October 2019 to investigate their structural evolution during fruit growth. The samples were characterized via High-performance anion exchange chromatography (HPAEC), Fourier transform–infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), thermogravimetric (TGA), pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and NMR (2D-heteronuclear single quantum coherence (HSQC) and 31P). The MWL samples in all fruit growth stages were GS-type lignin and lignin core undergoing minimal alterations during fruit development. The predominant linkage in the lignin structure was β-O-4′, followed by β-β' and β-5′. Galactose and glucose were the main monosaccharides associated with MWL. In MWL-6, the lignin exhibited the highest homogeneity and thermal stability. As the fruit matured, a gradual increase in the β-O-4′ proportion and the ratio of S/G was observed. The results provide comprehensive characterization of the cell wall lignin of quince fruit as it matures. This study could inspire innovative applications of quince fruit lignin and provide the optimal harvest time for lignin utilization.

Lignin bioconversion based on genome mining for ligninolytic genes in Erwinia billingiae QL-Z3

BackgroundBioconversion of plant biomass into biofuels and bio-products produces large amounts of lignin. The aromatic biopolymers need to be degraded before being converted into value-added bio-products. Microbes can be environment-friendly and efficiently degrade lignin. Compared to fungi, bacteria have some advantages in lignin degradation, including broad tolerance to pH, temperature, and oxygen and the toolkit for genetic manipulation.ResultsOur previous study isolated a novel ligninolytic bacterial strain Erwinia billingiae QL-Z3. Under optimized conditions, its rate of lignin degradation was 25.24% at 1.5 g/L lignin as the sole carbon source. Whole genome sequencing revealed 4556 genes in the genome of QL-Z3. Among 4428 protein-coding genes are 139 CAZyme genes, including 54 glycoside hydrolase (GH) and 16 auxiliary activity (AA) genes. In addition, 74 genes encoding extracellular enzymes are potentially involved in lignin degradation. Real-time PCR quantification demonstrated that the expression of potential ligninolytic genes were significantly induced by lignin. 8 knock-out mutants and complementary strains were constructed. Disruption of the gene for ELAC_205 (laccase) as well as EDYP_48 (Dyp-type peroxidase), ESOD_1236 (superoxide dismutase), EDIO_858 (dioxygenase), EMON_3330 (monooxygenase), or EMCAT_3587 (manganese catalase) significantly reduced the lignin-degrading activity of QL-Z3 by 47–69%. Heterologously expressed and purified enzymes further confirmed their role in lignin degradation. Fourier transform infrared spectroscopy (FTIR) results indicated that the lignin structure was damaged, the benzene ring structure and groups of macromolecules were opened, and the chemical bond was broken under the action of six enzymes encoded by genes. The abundant enzymatic metabolic products by EDYP_48, ELAC_205 and ESOD_1236 were systematically analyzed via liquid chromatography–mass spectrometry (LC–MS) analysis, and then provide a speculative pathway for lignin biodegradation. Finally, The activities of ligninolytic enzymes from fermentation supernatant, namely, LiP, MnP and Lac were 367.50 U/L, 839.50 U/L, and 219.00 U/L by orthogonal optimization.ConclusionsOur findings provide that QL-Z3 and its enzymes have the potential for industrial application and hold great promise for the bioconversion of lignin into bioproducts in lignin valorization.

Structure-property relationship between lignin structures and properties of 3D-printed lignin composites

Lignin is a low-cost and renewable bioresource with a huge annual production promising to prepare sustainable materials. However, the poor interfacial adhesion between many lignin-polymer pairs deteriorates the mechanical performance of the composites, which seriously limits the application of lignin in 3D printing via fused depositional modeling. This work examined lignin-polyamide 12 (PA 12) intermolecular interactions (e.g., hydrogen bonding) to address the interface challenge. To realize this goal, the phenolic hydroxyl content was increased for a kraft softwood lignin using a LiBr/HBr demethylation procedure, increasing phenoxy content by 61.7%. Increased hydrogen bonding interactions between modified lignin (Pine-Lig-OH) and PA 12 demonstrated a significantly improved molten dynamic modulus by rheological analysis. Regarding mechanical properties, by adding 20 wt% of Pine-Lig-OH, the tensile strength and Young's modulus reached 46.6 MPa and 1.62 GPa, 30.2% and 33.9% higher than PA 12, respectively. Further morphological analysis proved the interfacial interactions are enhanced by showing the difference in the phase gaps. The dynamic mechanical analysis (DMA) supported the conclusion that Pine-Lig-OH could interact with polymer chains, alternating segmental movements due to the strong interaction. This study presents a method to enhance lignin composite properties by promoting interactions with the polymer matrix through modified functional groups, guiding future lignin composite research.

What is lignin - the evolution of views (review)

The review considers changes in ideas about the biosynthesis, structure and functions of lignin in plants, starting from early mentions and up to the present. Alternative points of view on the process of lignin biosynthesis, its spatial and supramolecular structure, and the nature of lignincarbohydrate bonds are presented. 
 A special place in the review is occupied by the results of studies of lignin modification with the aim of reducing the content and changing the composition of monomer units by genetic engineering methods. Comparison of the structure of lignins isolated from transgenic and mutant trees, as well as herbaceous plants, showed that lignin biosynthesis is plastic and, in addition to canonical monolignols (coniferyl, synapic, and coumaric alcohols), other phenolic compounds can also participate in it.
 The study of the so-called "stress lignins" showed that lignin plays an important role in protecting plants from adverse environmental influences: mechanical damage, drought, low temperatures, pathogens, etc.
 The results of studies of the genetic modification of lignin made it possible to outline a program for directed modification of the biosynthesis process in order to obtain designer lignins, i.e. lignins with desired properties. This group also includes the so-called zip-lignins. They are distinguished by the presence of ester bonds between phenylpropane units.
 It is noted that, when conducting research in the field of genetic engineering, it is necessary to find a compromise between improving the processing of plant materials due to the modification of lignin and the viability of transgenic plants.

1-D Carbon Nano-Coils Derived from Almond Skin: Exhibiting Density of State, Diffusivity, Electron Transfer Rate, and Dopamine Redox Modulation Properties Akin to Graphene Oxide.

The quest to develop graphene-like biomass-carbon for advanced biomolecule redox modulation and sensing remains a challenge. The primary obstacle is the limited ability of biomass to undergo extensive graphitization during pyrolysis resulting in the formation of amorphous carbon materials with a small carbon-double-bond-carbon domain size (Lsp2), density of state (LDOS), ion diffusivity (D), and electron transfer rate constant (Ks). Herein, using almond skin (AS) the morphology of biomass is demonstrated as the key to overcoming these limitations. AS consists of 1D syringyl/guaiacyl lignin nano-coils which under H2/H2 annealing transform into pyrolytic 1D carbon nano-coils (r-gC). Spectroscopy and microscopy analyses reveal that the sheet layering structure, crystallinity, LDOS, and Lsp2 of r-gC mimic those of graphene oxide (GO). Moreover, its unique 1D morphology and profound microstructure facilitate faster charge transfer and ion diffusion than GO's planar structure, leading to better redox modulation and sensing of the neurotransmitter dopamine (DA) in physiological fluids. r-gC's DA detection limit of 3.62nM is below the lower threshold found in humans and on par with the state-of-the-art. r-gC is also DA-selective over 14 biochemicals. This study reveals that biomasses with well-defined and compact lignin structures are best suited for developing highly electroactive graphene-like biomass carbon.

Understanding Manganese Peroxidase-Catalyzed Conversion of the Lignin Structure and Its Application for the Polymerization of Kraft Lignin

Understanding Manganese Peroxidase-Catalyzed Conversion of the Lignin Structure and Its Application for the Polymerization of Kraft Lignin

Extraction and characterisation of kudzu root residue lignin based on deep eutectic solvents.

Lignin has great potential as the most abundant renewable phenolic polymer. Studies have shown that lignin structure varies depending on different sources and different extraction methods. However, there are few studies on lignin in kudzu root residue. The aim of the study was to explore optimal extraction conditions of Pueraria lobata residue lignin (PLL) with deep eutectic solvents (DESs) and characterise the structure and morphology of PLL. Firstly, the chemical composition of kudzu root residue was determined by the Van-soest method. Then, betaine was used as hydrogen bond acceptor (HBA), nine kinds of common acids and alcohol were selected as hydrogen bond donor (HBD) to synthesise a DES to extract lignin from kudzu root residue. The influence of conditions on the extraction of PLL was explored by a betaine-based DES according to a single-factor experiment, and then the best process of PLL extraction was determined by an orthogonal experiment. Finally, the morphology and structure of PLL were analysed by scanning electron microscope (SEM), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and NMR. Cellulose, hemicellulose, lignin, and ash content in kudzu root residue were 41.13%, 16.39%, 25.03%, and 0.41%, respectively. When the DES consisted of betaine and formic acid, the solid-liquid ratio was 1:45, the extraction time was 5.5 h at 160°C, the extraction yield of lignin was 89.29%, and the purity was 83.01%. PLL was composed of interconnected spherical particles with good thermal stability and narrow polydispersity index (PDI) distribution. FTIR and 2D-heteronuclear singular quantum correlation (HSQC) NMR illustrated that PLL was a typical G-type and S-type lignin. This study would fill the gap of research on lignin in kudzu root residue and provide a theoretical reference for the utilisation of lignin in kudzu roots as well as a new thinking for the recycling of kudzu root resources.

Morphology and structure control of lignin-derived hierarchical porous carbon for high-performance supercapacitors

Lignin-derived porous carbon (LDPC) is a low-cost and sustainable electrode material for supercapacitors. However, the complex three-dimensional amorphous structure of lignin brings challenges to the morphology and structure control of LDPC, which limits the electrochemical performance of these electrodes. Herein, a series of LDPCs with different particle morphologies and hierarchical pore structures are prepared by spray drying and KOH activation. It is found that the morphology and structure of LDPCs can be effectively controlled by adjusting the spray drying temperature and KOH ratio. A systematic investigation has been conducted on the relationship between the morphology and structure of LDPCs and their electrochemical performance. The preferred LDPC exhibits excellent electrochemical performance, showing high specific capacitances of 372.5 F g−1 and 264.8 F g−1 at current densities of 0.2 A g−1 and 20 A g−1, respectively, in the three-electrode test. The symmetric supercapacitor assembled with the LDPC electrode material exhibits superior cycling stability and energy density. After 10000 cycles of continuous charging and discharging at current density of 1 A g−1, the specific capacitance retention is as high as 96.4%. When the power density is 493.3 W kg−1, the energy density reaches ∼9.1 Wh kg−1. This work offers a viable method for regulating the morphology and structure of LDPC electrode material for high-performance supercapacitor application.

Kinetic understanding of fiber surface lignin effects on cellulase adsorption and hydrolysis

Cellulase hydrolysis is strongly affected by adsorption, which is inhibited by the non-productive binding between cellulase and lignin. However, lignin-bonded cellulase has also been found to be active in hydrolysis. Thus, in this work, lignin effects on cellulase adsorption and hydrolysis were studied using fibers with various surface lignin contents and structures based on kinetics. The surface lignin was changed by mechanical refining. Cellulase adsorbed on lignin showed reactivity to hydrolyze cellulose nearby according to the kinetic results, which is, however, much weaker compared with that by cellulose-bonded cellulase. With the decrease of surface lignin, this reactivity is also decreasing. Both cellulase adsorption and hydrolysis were increasing at first and then decreasing with the decrease of surface lignin as well as the lignin re-adsorption. It was concluded that lignin plays an important role in cellulase adsorption and non-productive binding occurs more easily between cellulase and the re-adsorbed lignin, as well as the residual lignin. At a relatively high surface lignin level, lignin structural and distribution changes were found to have a better effect on cellulase hydrolysis compared with lignin removal.

Effect of lignin on the formation of polycyclic aromatic hydrocarbons in smoked and grilled meat products

In order to explore the influence of wood types on formation of polycyclic aromatic hydrocarbons (PAHs) in traditional smoked and grilled meat products, the effect of lignin in woods on formation of PAHs was investigated in meat model systems. The results showed that PAHs formation was much dependent on the heating conditions. The addition of lignin led to significantly increased PAHs, which being connected with lignin structure. In comparison, the formation of PAHs was more facilitated by lignin with G structure than that with G/S structure. However, further study of adding lignin precursors demonstrated that lignin precursors with S structure were more favorable to the formation of PAHs than those with G structure. It was proposed that the relative content and activity of G/S structure of lignin in wood played a significant role in the formation of PAHs, which might provide theoretical reference for inhibition of PAHs fundamentally.

Lignin carbon-initiated Ni/K/Mo2C catalyst for efficient synthesis of higher alcohols from syngas

Bamboo lignin, the principal constituent of non-wood pulping black liquor, is ecologically and environmentally harmful due to its complex molecular structure and stability. Additionally, the syngas-based synthesis of higher alcohols is a desired industrial application, alleviating the dependency on petroleum resources. However, developing highly efficient catalysts with high space–time yield and selectivity towards higher alcohols remains challenging. Herein, for the first time, taking into account the permeable structure of bamboo lignin in paper-making black liquid resulting from cellulose and hemicellulose extraction, porous nano molybdenum carbide was manufactured by designed pretreatment and activation processes of the lignin, which was further doped by the K and Ni additive to create a highly efficient catalyst (Ni/K/Mo2C@LC) for the high alcohols synthesis reaction, yielding a surprising space–time yield of 0.455 g/gcat/h) to alcohol products under the optimal reaction conditions. Control experiments and characterizations were conducted over relevant catalysts, revealing that Ni and K could be integrated to regulate the adsorption property, acidity/basicity, and carbon chain growth ability of the catalysts. Also, the open mesoporous lignin carbon provided larger metal particles, enhancing the hydrogenation ability and better balancing the non-dissociative and dissociative active sites for the high alcohol synthesis reaction. These results provide insights into the structure design of carbide catalysts toward efficiently utilizing industrial lignin and other biomass-derived feedstocks, and the development of an efficient Mo-based catalyst for syngas conversion.

Influence of habitat, density, lignin structure, and extraction treatment on thermal-softening properties of water-swollen wood: a study of 87 wood specimens

Abstract This study aims to reveal the diversity of thermal-softening temperatures and identify the factors that determine this temperature. To achieve this, the thermal-softening properties of the radial direction of wood were measured under water-saturated conditions for 15 softwood and 72 hardwood specimens. Wood samples were obtained from the xylarium of the Forestry and Forest Products Research Institute, Japan. A dynamic viscoelastic measurement was performed on samples with uniform heating and cooling history because the difference in cooling rate can alter in the mechanical properties of wood. The storage and loss elastic moduli increased linearly as wood density increased, regardless of the wood species. However, the thermal-softening temperature (defined in this study as the peak temperature of loss tangent) was unrelated to the density, anatomical features, species, latitude, and annual rainfall in the habitat. When the relationship between thermal-softening temperature and lignin structure was investigated, a negative correlation was observed between the thermal-softening temperature and the syringyl ratio (syringyl/(syringyl+guaiacyl)) of lignin aromatics. This indicates that the thermal-softening temperature is higher for wood species with denser lignin structures, supporting the prior research showed correlation between thermal-softening temperature and methoxyl group content of wood.

Double in-situ lignin modification in surfactant-assisted glycerol organosolv pretreatment of sugarcane bagasse towards efficient enzymatic hydrolysis

Organosolv pretreatment effectively fractionates lignocellulosic biomass for efficient enzymatic hydrolysis, yielding fermentable sugars. However, substantial lignin redeposition on the substrate surface and residual lignin content exacerbate lignin’s inhibitory effects on subsequent enzymatic hydrolysis. An in-situ lignin modification is proposed to address this challenge by incorporating polyethylene glycol (PEG) series into glycerol organosolv (GO) pretreatment. According to the results obtained, PEG-assisted GO pretreated substrate exhibited significantly increased sugar yield during enzymatic hydrolysis, particularly with PEG 4000, showing 35.4% higher glucose yield over 72 h. The improved glucose yield with PEG could be attributed to changes in the physicochemical structure and properties of residual lignin, mitigating its non-productive interaction with cellulase enzymes. PEG's presence in GO pretreatment also increased β-O-4 linkages preservation by 55% and reduced phenolic hydroxyl groups by 28% in lignin fragments versus no surfactants. This outcome resulted from introducing glycerol and PEG hydroxyl tails into the lignin structure, forming α-etherified lignin and rendering it more hydrophilic. Simulations confirmed strong Van Der Waals and hydrogen bonding interactions between lignin units and PEG, hindering lignin fragments repolymerization. Incorporating PEG in the organosolv pretreatment proves highly beneficial for cellulase-mediated lignocellulosic biorefinery, resembling a lignin-first strategy. The optimized process enables efficient biomass utilization for sustainable fuels and chemicals production.