Lignin Structure Research Articles

Recent Progress in Electrocatalytic Conversion of Lignin: From Monomers, Dimers, to Raw Lignin.

Lignin, as the second largest renewable biomass resource in nature, has increasingly received significant interest for its potential to be transformed into valuable chemicals, potentially contributing to carbon neutrality. Among different approaches, renewable electricity-driven biomass conversion holds great promise to substitute a petroleum resource-driven one, owing to its characteristics of environmental friendliness, high energy efficiency, and tunable reactivity. The challenges lie on the polymeric structure and complex functional groups in lignin, requiring the development of efficient electrocatalysts for lignin valorization with enhanced activity and selectivity toward targeted chemicals. In this Review, we focus on the advancement of electrocatalytic valorization of lignin, from monomers, to dimers and to raw lignin, toward various value-added chemicals, with emphasis on catalyst design, reaction innovation, and mechanistic study. The general strategies for catalyst design are also summarized, offering insights into enhancing the activity and selectivity. Finally, challenges and perspectives for the electrocatalytic conversion of lignin are proposed.

Lattice Strain Engineering on Metal-Organic Frameworks by Ligand Doping to Boost the Electrocatalytic Biomass Valorization.

As an efficient and environmental-friendly strategy, electrocatalytic oxidation can realize biomass lignin valorization by cleaving its aryl ether bonds to produce value-added chemicals. However, the complex and polymerized structure of lignin presents challenges in terms of reactant adsorption on the catalyst surface, which hinders further refinement. Herein, NiCo-based metal-organic frameworks (MOFs) are employed as the electrocatalyst to enhance the adsorption of reactant molecules through π-π interaction. More importantly, lattice strain is introduced into the MOFs via curved ligand doping, which enables tuning of the d-band center of metal active sites to align with the reaction intermediates, leading to stronger adsorption and higher electrocatalytic activity toward bond cleavage within lignin model compounds and native lignin. When 2'-phenoxyacetophenone is utilized as the model compound, high yields of phenol (76.3%) and acetophenone (21.7%) are achieved, and the conversion rate of the reactants reaches 97%. Following pre-oxidation of extracted poplar lignin, >10 kinds of phenolic compounds are received using the as-designed MOFs electrocatalyst, providing ≈12.48% of the monomer, including guaiacol, vanillin, eugenol, etc., and p-hydroxybenzoic acid dominates all the products. This work presents a promising and deliberately designed electrocatalyst for realizing lignin valorization, making significant strides for the sustainability of this biomass resource.

Modifying lignin composition and xylan O-acetylation induces changes in cell wall composition, extractability, and digestibility

BackgroundLignin and xylan are important determinants of cell wall structure and lignocellulosic biomass digestibility. Genetic manipulations that individually modify either lignin or xylan structure improve polysaccharide digestibility. However, the effects of their simultaneous modifications have not been explored in a similar context. Here, both individual and combinatorial modification in xylan and lignin was studied by analysing the effect on plant cell wall properties, biotic stress responses and integrity sensing.ResultsArabidopsis plant co-harbouring mutation in FERULATE 5-HYDROXYLASE (F5H) and overexpressing Aspergillus niger acetyl xylan esterase (35S:AnAXE1) were generated and displayed normal growth attributes with intact xylem architecture. This fah1-2/35S:AnAXE1 cross was named as hyper G lignin and hypoacetylated (HrGHypAc) line. The HrGHypAc plants showed increased crystalline cellulose content with enhanced digestibility after chemical and enzymatic pre-treatment. Moreover, both parents and HrGHypAc without and after pre-treating with glucuronyl esterase and alpha glucuronidase exhibited an increase in xylose release after xylanase digestion as compared to wild type. The de-pectinated fraction in HrGHypAc displayed elevated levels of xylan and cellulose. Furthermore, the transcriptomic analysis revealed differential expression in cell wall biosynthetic, transcription factors and wall-associated kinases genes implying the role of lignin and xylan modification on cellular regulatory processes.ConclusionsSimultaneous modification in xylan and lignin enhances cellulose content with improved saccharification efficiency. These modifications loosen cell wall complexity and hence resulted in enhanced xylose and xylobiose release with or without pretreatment after xylanase digestion in both parent and HrGHypAc. This study also revealed that the disruption of xylan and lignin structure is possible without compromising either growth and development or defense responses against Pseudomonas syringae infection.

Efficient and comprehensive utilization of sugarcane bagasse components through vanillic acid pretreatment

Lignocellulosic biomass, being a renewable carbon-based resource, holds paramount practical significance in terms of its comprehensive conversion and utilization for effectively substituting petroleum-based energy sources. Herein, we present a sustainable and environmental-friendly vanillic acid (VA) pretreatment approach for efficient and comprehensive utilization of sugarcane bagasse (SCB). The xylo-oligosaccharides (XOS)DP2-6 yield of 60.4 % (wt.% of xylan) was achieved under the conditions of 180 °C/15 min/6% VA (wt.% of SCB), while lignin condensation was simultaneously inhibited in this initial biorefinery stage. Subsequently, the enzymatic saccharification of the pretreatment residue was significantly enhanced due to the reduced cellulase adsorption of lignin. Lignin structural characterization demonstrated that VA could effectively incorporate to the lignin structure, resulting in the lignin exhibiting high preservation of β-O-4′ linkages (39.38/100 Ar), low molecular weight (2410 Da), abundant phenolic hydroxyl groups (3.70 mmol/g), and less degree of condensation (0.33). Importantly, the resulting less-condensed lignin (LCL) could effectively undergo melt-blending with poly(butylene adipate-co-terephthalate) (PBAT) owing to its low glass transition temperature, thereby facilitating the establishment of enhanced intermolecular interactions (π–π interaction and hydrogen bond) between LCL and PBAT. These interactions enhanced the plasticization of PBAT on LCL, and as a result, the prepared P/LCL30 composite film possessed excellent tensile properties without requiring lignin modification or additional additives. The study presents a straightforward and efficient biorefinery conversion strategy for lignocellulosic biomass, wherein hemicellulose was degraded into XOS, cellulose was enzymatically hydrolyzed to glucose, and the remaining lignin with lower condensation was utilized as a filler of PBAT composite film.

Quantifying the contribution of lignin to humic acid structures during composting

The transformation behavior of different types of lignin structure was investigated during composing with particular interest of revealing the contribution rate of lignin functional groups as well as their interaction to humic acids (HA). Rice straws, tree branches, and pine needles were selected as composting materials, because they predominantly contain G-S-H, G-S, and G-type lignin. Results showed that microorganisms were the driving force behind the conversion of lignin into HA. During composting, appeared different levels of cleavage, tearing, and fragmentation on the superficial lignin structures. In depth analysis of lignin transformation, lignin primarily consisted of aromatic groups, CO bonds, alkyl groups, hydroxyl groups and linkage between monomeric units (β-O-4, β-5 and β-β) in the early stage of composting. As lignin degraded, the CO bonds were gradually exposed. But due to their unstable nature, the CO bonds were prone to undergo changes with the cleavage of the aromatic rings at positions 2, 5, and 6 during composting. CO bonds could be converted into aromatic rings, alkyl groups, hydroxyl groups, and CO groups in HA. Through multiple linear regression analysis, it could be concluded that the CO bonds in G-type and S-type monomeric units contributed significantly to the aromatic rings, accounting for 30.4 % and 48.4 %, respectively. The main mechanism might be related to the cleavage of CO bonds and subsequent atomic rearrangement after the release of carbon atoms. This in-depth analysis filled the gap in the mechanism of HA formation during composting.

Controlling the graphite-like microcrystalline structure of lignin-based ultrafine carbon fibers via the design of condensed structures

Obtaining lignin-based graphite-like microcrystallites at a relatively low carbonization temperature is still very challenging. In this work, we report a new method based on condensed structures, for regulating graphite-like microcrystalline structures via the incorporation of 4,4′-diphenylmethane diisocyanate (MDI) into the main structure of lignin. The effects of MDI on the thermal properties of lignin and the graphite-like microcrystalline structure of lignin-based ultrafine carbon fibers were extensively studied and investigated. The incorporation of MDI decreased the thermal stability of lignin, increased the carbon yield and enhanced the formation of graphite-like microcrystallites, which are beneficial for reducing energy consumption during the preparation of lignin-based carbon fibers. The modified lignin-based ultrafine carbon fibers (M-LCFs) demonstrated satisfactory electrochemical performance, including high specific capacitance, low charge transfer resistance, and good cycle performance. The M-LCFs-3/2 electrode had a specific capacitance of 241.3 F g−1 at a current density of 0.5 A g−1, and a residual ratio of 90.2 % after 2000 charge and discharge cycles. This study provides a new approach to control the graphite-like microcrystalline structure and electrochemical performance while also optimizing the temperature.

Silica Biomineralization with Lignin Involves Si-O-C Bonds That Stabilize Radicals.

Plants undergo substantial biomineralization of silicon, which is deposited primarily in cell walls as amorphous silica. The mineral formation could be moderated by the structure and chemistry of lignin, a polyphenol polymer that is a major constituent of the secondary cell wall. However, the reactions between lignin and silica have not yet been well elucidated. Here, we investigate silica deposition onto a lignin model compound. Polyphenyl propanoid was synthesized from coniferyl alcohol by oxidative coupling with peroxidase in the presence of acidic tetramethyl orthosilicate, a silicic acid precursor. Raman, Fourier transform infrared, and X-ray photoelectron spectroscopies detected changes in lignin formation in the presence of silicic acid. Bonds between the Si-O/Si-OH residues and phenoxyl radicals and lignin functional groups formed during the first 3 h of the reaction, while silica continued to form over 3 days. Thermal gravimetric analysis indicated that lignin yields increased in the presence of silicic acid, possibly via the stabilization of phenolic radicals. This, in turn, resulted in shorter stretches of the lignin polymer. Silica deposition initiated within a lignin matrix via the formation of covalent Si-O-C bonds. The silica nucleants grew into 2-5 nm particles, as observed via scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. Additional silica precipitated into an extended gel. Collectively, our results demonstrate a reciprocal relation by which lignin polymerization catalyzes the formation of silica, and at the same time silicic acid enhances lignin polymerization and yield.

Multi-site sulfonation of lignin for the synthesis of a high-performance dye dispersant

Sulfonated lignin-based dye dispersants have intensively attracted attention due to their low cost, renewability and abundant sources. However, their utilization is limited by the low content of sulfonic groups and high content of hydroxyl groups in their complex lignin structure, which results in various problems such as high reducing rate of dye, severe staining of the fibers and uneven dyeing. Here, the multi-site sulfonated lignin-based dispersants were prepared with high sulfonic group content (2.20 mmol/g) and low hydroxyl content (2.43 mmol/g). When using it as the dispersant, the dye uptake rate was improved from 69.23 % to 98.55 %, the reducing rate was decreased from 20.82 % to 2.03 %, the K/S value was reduced from 0.69 to 0.02, and the particle sizes in dye system before and after high temperature treatment were stabilized below 0.5 μm. Besides, the dispersion effect was significantly improved because no obvious separation between dye and water was observed even if without the assistance of grinding process. In short, the multi-site sulfonation method proposed in this work could remarkably improve the performances of the lignin-based dye dispersants, which would facilitate the development of the dye dispersion and the high value utilization of lignin.

Phenolics production via the catalytic pyrolysis of organosolv lignin over praseodymium doped lanthanum nickelate

To fully utilize the aromatic ring structure of lignin and realize high value addition, organosolv lignin (OL) extracted from papermaking waste liquid was subjected to catalytic pyrolysis for the production of phenolic compounds. Using self-made carbon nanospheres as a template, cellular La0.8Pr0.2NiO3 perovskite was prepared by the sol-gel method and used as catalyst in the pyrolysis of OL at 600 °C for 3 h. The yield of liquid-phase product was 21.34 %, and the selectivity of phenolic compounds reached 70.20 %, constituting increases by 43.41 % and 25.87 % compared with the yield and selectivity of the catalyst-free process, respectively. After four cycles of regeneration, La0.8Pr0.2NiO3 perovskite still demonstrated good structural and catalytic stability. This work provides a theoretical basis for the development of green and sustainable chemical products.

Production of lignin monomeric alcohols and lipids from oil palm empty fruit bunch by a combination of alkaline nitrobenzene depolymerization and Lipomyces starkeyi bioconversion

The efficient valorization of lignocellulosic biomass into valuable chemicals represents a cornerstone for advancing sustainable bioeconomy practices. This study focuses on the innovative conversion of oil palm empty fruit bunch (OPEFB) into lignin monomeric alcohols and lipids through a novel two-step process combining alkaline nitrobenzene depolymerization and bioconversion by Lipomyces starkeyi. Initially, OPEFB undergoes alkaline nitrobenzene depolymerization to break down complex lignin structures into monomeric aldehydes. The resulting derivates serve as substrates for the bioconversion by L. starkeyi, which is competent at metabolizing lignin-derived compounds into higher-value lignin monomeric alcohols (syringyl, vanillyl, and 4-hydroxybenzyl alcohol) and lipids, simultaneously. The strategy delineates the optimization of depolymerization conditions, sodium hydroxide concentration, nitrobenzene effect, and reaction time to maximize the yield of depolymerized lignin suitable for bioconversion. Subsequently, the bioconversion process toward cell growth, lipid production, and fatty acid profiles in various fermentations by L. starkeyi was explored. The highest syringaldehyde and vanillin obtained reached up to 4.81 mM and 0.64 mM, respectively. Then, it successfully produced 3.57 mM and 0.40 mM of syringyl alcohol and vanillyl alcohol, respectively, with 5.86 g L−1 of the lipid titer. The study demonstrates the potential of this integrated approach to convert OPEFB into valuable lignin-derived biochemicals and lipids, thereby contributing to the development of alternative strategies for biomass utilization efficiently.

Enhancing biogas production through photocatalytic pretreatment of rice straw co-digested with cow dung and food waste using a novel g-C3N4/SiO2/bentonite catalyst

This study investigates the application of a novel composite photocatalyst, g-C3N4/SiO2/ Bentonite, for rice straw pretreatment, aiming to enhance biogas production in anaerobic digestion. The photocatalytic pretreatment disrupts rice straw's lignin and hemicellulose structures, reducing silica content for improved microbial degradation. Five 2 L anaerobic digesters were employed with rice straw as the substrate and co-digestion materials, including cow dung and food waste. Rice straw treated with the g-C3N4/7.5% SiO2/5% Bentonite catalyst exhibited a remarkable 37% increase in methane yield compared to untreated rice straw. This photocatalytic process led to a 31% increase in cellulose content and a 30% reduction in lignin after 6 hours of pretreatment. Simultaneously, silica content in the rice straw decreased to 6.4% after 6 hours, resulting in a 48% increase in the carbon proportion. These findings underscore the potential of integrated photocatalysts for significantly enhancing biogas production efficiency through the pretreatment of lignocellulosic biomass.

Analysis of Aroma Components of Enzymatic Hydrolysis Products of Oak Lignin from Different Producing Areas

The morphology and structure of lignin in French oak, American oak and Chinese Mongolian oak were observed and compared by scanning electron microscopy (SEM). The results showed that the surface of lignin after enzymatic hydrolysis was more irregular and the contact area was obviously increased. GC-MS detected 3 kinds of lignin, 4 kinds of components and 30 kinds of volatile substances. The lignin content of French oak was the highest (8911.5 ± 512.2 μg/L, 29 kinds), followed by that of American oak (8071.7 ±541.9 μg/L, 26 kinds), and that of Mongolian oak was the least (7903.3 ± 492.5 μg/L, 26 kinds). The results of aroma characteristics analysis, principal component analysis and heat map analysis showed that the aroma components of the three kinds of oak lignin were significantly different. French oak lignin could provide more volatile phenols, with obvious smoky, woody and sweet flavor. Mongolian oak lignin carries more phenolic and ester compounds, providing a relatively soft floral, fruity flavor. American oak lignin has a relatively average aroma substance content, which can bring strong and complex complex aroma characteristics.

Activated Carbon Application Simultaneously Alleviates Paddy Soil Arsenic Mobilization and Carbon Emission by Decreasing Porewater Dissolved Organic Matter.

Flooding of paddy fields during the rice growing season enhances arsenic (As) mobilization and greenhouse gas (e.g., methane) emissions. In this study, an adsorbent for dissolved organic matter (DOM), namely, activated carbon (AC), was applied to an arsenic-contaminated paddy soil. The capacity for simultaneously alleviating soil carbon emissions and As accumulation in rice grains was explored. Soil microcosm incubations and 2-year pot experimental results indicated that AC amendment significantly decreased porewater DOM, Fe(III) reduction/Fe2+ release, and As release. More importantly, soil carbon dioxide and methane emissions were mitigated in anoxic microcosm incubations. Porewater DOM of pot experiments mainly consisted of humic-like fluorophores with a molecular structure of lignins and tannins, which could mediate microbial reduction of Fe(III) (oxyhydr)oxides. Soil microcosm incubation experiments cospiking with a carbon source and AC further consolidated that DOM electron shuttling and microbial carbon source functions were crucial for soil Fe(III) reduction, thus driving paddy soil As release and carbon emission. Additionally, the application of AC alleviated rice grain dimethylarsenate accumulation over 2 years. Our results highlight the importance of microbial extracellular electron transfer in driving paddy soil anaerobic respiration and decreasing porewater DOM in simultaneously remediating As contamination and mitigating methane emission in paddy fields.

Delignification of wood fibers using a eutectic carvacrol–methanesulfonic acid mixture analyses of the structure and fractional distribution of lignin, cellulose, and hemicellulose

AbstractDelignification and fractional pretreatments are essential for valorization of wood biomass in various bioproducts. Herein, lignocellulose wood fibers were exposed to a eutectic mixture (EM) of carvacrol and methanesulfonic acid for different times. The resulting structural and chemical alterations in biomass were explored in terms of the fiber morphology and fractional chemical composition through fiber image analysis, field-emission scanning electron microscopy, high-performance liquid chromatography, and a novel approach based on fluorescence-lifetime imaging microscopy (FLIM). The autofluorescence of the lignocellulose fibers, which was primarily due to lignin with contributions from cellulose and hemicellulose, enabled application of FLIM in lignocellulose compositional analysis in micro-scale. FLIM analysis revealed that EM treatment efficiently removed lignin from the outer fiber layers. Furthermore, the effective EM treatment time was 3 h (with a residual lignin content of ~ 7 wt%), after which defects were observed on the fibers and the cellulose chains started breaking. This degradation was also indicated by a shift of the lifetime spectra toward the fluorescence lifetime of cellulose with increasing treatment time. Overall, our findings provide valuable insights to the response of lignocellulose fibers to EM treatment, contributing to the important goal of wood biomass application in bioproducts.

From technical lignin to native lignin: Depolymerization, functionalization, and applications

Lignocellulose as a form of biomass is inedible. It represents a renewable feedstock for the synthesis of chemicals and materials. Its utilization has become an area of growing interest. Of lignocellulose components, lignin is comparatively under-explored and under-utilized, despite its abundance. This Focus Review recognizes this missed opportunity and presents a concise overview on some of the most recent progress involving the generation and application of functional materials derived from lignin. Between the two commonly encountered forms of lignin, technical lignin is a by-product of the paper production industry and is highly processed under harsh conditions. As such, it has generally been used for filler and resin materials. By comparison, native lignin is rich in chemical functionalities and holds great promise for downstream chemical synthesis. In recognition of these potentials, “lignin-first” strategies have emerged to directly convert native lignin to building blocks rich in functional groups, such as alcohols and carbonyls, while maintaining the integrity of the aromatic structures in lignin. The lignin-first strategy complements the already well explored field of technical lignin utilization. These chemoselective, lignin-first methods promise routes to native lignin valorization into high-value building blocks while keeping cellulose and hemicellulose intact and, therefore, are particularly appealing. This Focus Review first recognizes the importance of the traditional strategies for technical lignin utilization and highlights some of the newest developments. It then puts an emphasis on these lignin-first approaches for improved native lignin utilizations.

Temporal dynamics of lignin degradation in Quercus acutissima sawdust during Ganoderma lucidum cultivation

Despite a fair amount of lignin conversion during mycelial growth, previous structural analyses have not yet revealed how lignin changes continuously and what the relationship is between lignin and ligninolytic enzymes. To clarify these aspects, Quercus acutissima sawdust attaching Ganoderma lucidum mycelium collected from different growth stage was subjected to analysis of lignin structure and ligninolytic enzyme activity. Two key periods of lignin degradation are found during the cultivation of G. lucidum: hypha rapid growth period and primordium formation period. In the first stage, laccase activity is associated with the opening of structures such as methoxyls, β-O-4′ substructures and guaiacyl units in lignin, as well as the shortening of lignin chains. Manganese peroxidases and lignin peroxidases are more suitable for degrading short chain lignin. The structure of phenylcoumarans and syringyl changes greatly in the second stage. The results from sawdust attaching mycelium provide new insights to help improve the cultivation substrate formulation of G. lucidum and understand biomass valorization better.

Identification of volatile organic compound of oil palm plants infected with Ganoderma sp.

The success of controlling basal stem rot (BSR) disease caused by Ganoderma sp. is mostly determined by the early detection of the fungi. Hence, when the signs of infection begin to appear, plants are generally difficult to rescue since the pathogen infection has spread widely to all parts of the plant. Therefore, early detection through the application of biosensors for Ganoderma sp. infection is absolutely necessary. This study aim was to identify biomarker compounds of Ganoderma sp. infection in oil palm plants with GC-MS for volatile compounds, and LC-MS for non-volatile compounds. The results showed that Ganoderma sp. mycelium produced pyrimidinamine compounds. Meanwhile in early infected nursery plants, were found benzo[h]quinoline, hexaoxa-7,9,11-trisilaheptad, tris-(trimethyl-silyl ester and methyl-tris(trimethyl-siloxy)-silane). Whereas in Bekri, Rejosari, and Adolina plantation, the compound methyl-tris(trimethyl-siloxy)-silane was also found in healthy mature plants. GC-MS test results showed that for early, moderate and severe plants produced several benzene derivative compounds such as ethylbenzene, xylene, and benzaldehyde. These compounds were assumed to be resulted from the breakdown of the lignin structure which build plant cell walls, and have potency to be used as marker compounds for early infected Ganoderma sp. detection. The result of the produced gas quantification concluded that in the produced oil palm plants released less CO2 compared to healthy plants. On the other hand, the NH3 produced was higher than the healthy plants. Meanwhile, two non-volatile compounds were found that they were only produced by infected trunk and root tissue, namely pseudobrucine and picrasidine.

Unveiling the mechanism of lignin nanofiller in boosting the performance of triboelectric nanogenerators

Lignin has been demonstrated as the tribopositive nanofillers in boosting the triboelectric performances of biopolymer-based triboelectric nanogenerators (TENGs). However, the complex structures of lignin caused the unclear understanding how the molecular structures of lignin affected the output performances of TENGs. Herein, for the first time, five fractionated lignin with different structures were innovatively employed as the tribopositive nanofillers in CMC. Computational simulations and experimental results verified that the lignin with more S units, A-type linkage and large molecular weight give rise to the higher dielectric constant as well as the triboelectric performances. Relying on this principle, the acetone lignin possessed the highest dielectric behavior and the constructed TENG delivered the maximum Voc of 204.34 V, Isc of 6.86 µA, Qsc of 70.27 nC and instantaneous output power density of 836.64 mW/m2 under contact frequency of 1 Hz. Moreover, such biofilm can be dissolved in water and the regenerated film delivered stable output performances at least 5 times. Our findings not only provided the in-depth understanding of the relationship between triboelectrification behaviors and molecular structures of lignin, but also boosted the rational designing high-performance lignin-based tribopositive nanofillers for self-powered sensing or mechanical energy harvesting.

Lignin's complex role in lignocellulosic biomass Recalcitrance: A case study on bamboo

Lignin is widely recognized as a key factor influencing the recalcitrance of lignocellulosic biomass, yet the specifics of this relationship remain complex and not fully understood due to the complex interplay between lignin content variation and cell wall structure. Bamboo, which exhibits greater recalcitrance compared to wood in biorefinery processing, was chosen as the focus of investigation in this study. Three variants of Dendrocalamus farinosus with high, middle and low lignin contents were systematically analyzed and compared, in terms of molecular structure of lignin, hemicelluloses and cellulose, cell wall polymer spatial orientation, lignin-carbohydrate complex (LCC) linkages, cell wall geometrical size, as well as deconstruction efficiency, including delignification, alkaline extraction, and cellulose enzymatic hydrolysis efficiency. Findings reveal that an increase in lignin content generally lowers bamboo's deconstruction efficiency, but the mechanisms are more nuanced than previously thought. While lignin content variations do not significantly affect the molecular structure of xylan, cellulose and the chemical linkage type of LCC linkages, they do impact cellulose crystallinity, xylan orientation and notably, the thickness of fiber cell wall in the free fiber stands of bamboo. These findings highlight that lignin's role extends beyond mere physical protection of the cell wall, but also induces subtle variations in polymer structure and cell wall morphologies, which collectively influence the deconstruction efficiency of bamboo cell walls.

Modulating the properties and structure of lignins produced by alkaline delignification of sugarcane bagasse pretreated with two different mineral acids at pilot-scale

Sugarcane bagasse was pretreated with dilute phosphoric acid or sulfuric acid to facilitate cellulose hydrolysis and lignin extraction. With phosphoric acid, only 8 % of the initial cellulose was lost after delignification, whereas pretreatment with sulfuric acid resulted in the solubilization of 38 % of the initial cellulose. After enzymatic hydrolysis, the process using phosphoric acid produced approximately 35 % more glucose than that using sulfuric acid. In general, the lignins showed 95–97 % purity (total lignin, w/w), an average molar mass of 9500–10,200 g mol−1, a glass transition temperature of 140–160 °C, and a calorific value of 25 MJ kg−1. Phosphoric acid lignin (PAL) was slightly more polar than sulfuric acid lignin (SAL). PAL had 13 % more oxidized units and 20 % more OH groups than SAL. Regardless of the acid used, the lignins shared similar properties, but differed slightly in the characteristics of their functional groups and chemical bonds. These findings show that pretreatment catalyzed with either of the two acids resulted in lignin with sufficiently good characteristics for use in industrial processes.