Lignin Removal Research Articles

The Effect of Alkalization on the Mechanical Properties of Sansevieria Fiber Bio-Composit

Alkali treatment of natural fibers has a role in removing hemicellulose and lignin layers. This layer prevents the matrix from bonding with the natural fiber cellulose structure. The use of an inappropriate type of alkali will reduce its effectiveness and can even damage the cellulose layer. This study compared the effectiveness of alkaline NaOH, CaOH and KOH in removing lignin and hemicellulose and their ability to maintain cellulose content. The use of the immersion method in alkaline solutions is well controlled. The FTIR characterization test was used to detect functional group changes, the TGV test to detect heat resistance ability, the XRD test to detect structural changes in crystalline and amorphous properties of sansevieria natural fibers. Furthermore, the tensile test to determine the effect of alkaline treatment on changes in mechanical strength Tensile strength. From the test results it was found that the alkaline NaOH gave the best characteristics by detecting the presence of cellulose, tensile strength and the nature of the crystalline atomic structure.
 Highlights: 
 
 Effectiveness of Alkali Types: Comparison of NaOH, CaOH, and KOH effectiveness in removing lignin and hemicellulose while preserving cellulose content.
 Characterization Techniques: FTIR, TGA, and XRD tests used for functional group changes, heat resistance, and structural properties evaluation.
 NaOH Superiority: Alkaline NaOH treatment demonstrated best results in maintaining cellulose, enhancing tensile strength, and influencing atomic structure.
 
 Keywords: Alkali treatment, Natural fibers, Lignin removal, Cellulose preservation, Tensile strength.

A novel mineral-acid free biphasic deep eutectic solvent/γ-valerolactone system for furfural production and boosting the enzymatic hydrolysis of lignocellulosic biomass

The failure of hemicellulose valorization in a deep eutectic solvent (DES) pretreatment has become a bottleneck that challenges its further development. To address this issue, this study developed a DES/GVL (γ-valerolactone) biphasic system for effective hemicellulose-furfural conversion, enhanced cellulose saccharification and lignin isolation. The results indicated that the biphasic system could significantly improve the lignin removal (as high as 89.1%), 86.0% higher than the monophasic DES, accompanied by ∼100% hemicellulose degradation. Notably, the GVL in the biphasic solvent restricted the condensation of hemicellulose degradation products, which as a result generated large amount of furfural in the pretreatment liquid with a yield of 68.6%. With the removal of hemicellulose and lignin, cellulose enzymatic hydrolysis yield was boosted and reached near 100%. This study highlighted that the novel DES/GVL is capable of fractionating the biomass and benefiting their individual utilization, which could provide a new biorefinery configuration for a DES pretreatment.

Microwave-assisted formic acid/cold caustic extraction for separation of cellulose and hemicellulose from biomass

Effective separation of cellulose and hemicellulose from lignocellulosic biomass is an essential step for creating high-value products. In this study, a modified treatment process was proposed for cellulose purification via microwave-assisted formic acid catalytic hydrolysis followed by cold caustic extraction. The sugar content in the extract was determined using UV spectrophotometer and dual-wavelength visible spectrophotometry. Combined microwave-assisted formic acid (M-FA) with cold caustic extraction (CCE) treatments achieved rapid separation and removal of hemicelluloses from waste hardwood pulp fibers. The hemicelluloses content decreased from 28.6% to 2.3%, and the lignin content changed from 27.8% to 6.1%, which resulted in a maximal cellulose content of 91.5% under the optimal M-FA/CCE treatment conditions. In addition, the crystallinity index of pulp fibers increased from 54.3% to 67.1%, and the initial decomposition temperature decreased from 335.4 to 270.2 °C with the decrease of hemicellulose and lignin content. The modified process provided a sustainable and effective method for hemicellulose separation and lignin removal from cellulosic fibers.

Evaluating performance of CrCl3-catalyzed ethanol pretreatment of poplar on cellulose conversion

As green and effective depolymerization processes, CrCl3 and CrCl3-catalyzed ethanol pretreatment were comprehensively investigated to improve cellulose conversion from pretreated residues in poplar in the present study. The influence of pretreatment temperature on delignification, structural characteristics of lignin, and the yield of glucose and ethanol was comparatively analyzed to emphasize the synergy effect of CrCl3 and ethanol solvent. Particularly, CrCl3-catalyzed ethanol pretreatment at 200 °C resulted in the pretreated substrates with >94% removal of hemicellulose and lignin, consequently reaching 88.88% and 56.11% yields of glucose and ethanol, respectively. Lignin's structural change was observed by Gel permeation chromatography and 2D nuclear magnetic resonance spectroscopy and its relationship with the efficiency of enzymatic hydrolysis and fermentation was determined. Results indicated that the increased pretreatment temperature enhanced the lignin depolymerization with smaller molecular weight, fewer β-O-4 linkages, and higher S/G ratio, especially in CrCl3-catalyzed ethanol pretreatment, which was positively associated with poplar cellulose conversion. In addition to offering a comprehensive illustration of the sugar/ethanol generation during CrCl3-catalyzed organosolv pretreatment, this work also provided theoretical support for biofuel and biochemical production from poplar.

The coupling effects between acid-catalyzed hydrothermal pretreatment and acidic/alkaline deep eutectic solvent extraction for wheat straw fractionation

Mild hydrothermal pretreatment (HP) integrating with solvent extraction is a promising two-step technique to enhance the overall lignin and carbohydrate output for lignocellulose fractionation. This work comparatively assessed the coupling effect between mild HP (the first step) and the emerging acidic choline chloride-natural acid or alkaline choline hydroxide based deep eutectic solvents (DES, the second step) for wheat straw fractionation. It was shown HP with 0.3% p-toluenesulfonic acid (p-TsOH) catalyst achieved a good compromise between complete hemicellulose removal (nearly 100%) and high cellulose recovery (99.2%). While choline hydroxide based DES showed better coupling effect with HP than choline chloride-natural acid DES, corresponding to 75.6 and 31.2% lignin removal respectively. It was proposed that the alkaline DES enhanced lignocellulose swelling the lignin phenolic hydroxyl groups deprotonation and thus facilitating lignin solubilization despite of its condensation at HP. Therefore, the alkaline DES resulting cellulose-rich fraction exhibited higher potential for further processing.

Performance evaluation of treated coconut fibre in cementitious system

In this study, concentrated cement pore solution (CPS) was prepared and coconut fibre was soaked in it, to mimic worst condition of cementitious medium. Four coconut fibre samples were studied; the first was untreated fibre (NT), the second sample was NaOH treated fibre, while the third and fourth samples were NT and NaOH fibres soaked in CPS for 28 days, respectively. Each fibre was characterized by determining their physical and mechanical properties. Hydrophilic/hydrophobic characters were determined by measuring contact angles in water, while surface morphology of the fibre samples were studied with the aid of scanning electron microscopy. EDS was used to determine the elemental composition of the fibres, while Thermogravimetric analysis was performed to assess thermal stability of the fibre samples. Crystallinity of the fibres as well as the functional group composition present in each fibre samples, was determined using XRD and FTIR respectively. The results showed that fibres treated with NaOH and those exposed to CPS had higher densities (1.94 g/cm3) than untreated fibre (1.64 g/cm3), while the tensile strength was greatly increased by about 120%. SEM images of the fibres indicated that NaOH and CPS caused removal of lignin and hemicellulose, making the lumens to be smaller compared to untreated fibre. Similarly, crystallinity of the fibre was increased due to NaOH and CPS treatment, compared to the untreated fibres. CPS was found to improve thermal stability of the fibres. It was concluded that CPS did not pose any threat to performance of fibre.

Effects of various acid catalysts in dimethyl isosorbide/water co-solvent system for lignocellulosic biomass pretreatment

Novel organosolv pretreatments of biomass using biobased green solvents have attracted increasing attention to realize sustainable biorefinery. We have demonstrated that the feasibility of dimethyl isosorbide/water co-solvent in fractionating lignocellulosic biomass (Eucalyptus) for multiple products under a mild condition (120 °C, 60 min). To take a further step towards revealing the effects of catalysts, we explored various Brønsted (e.g., H2SO4, HCl, and p-TsOH), Lewis acid catalysts (e.g., AlCl3 and FeCl3) and their combinations in this co-solvent system. An interesting finding was that the delignification efficiency of AlCl3 was lower than that of H2SO4 (69.9% vs 91.2%), while the cellulose conversion efficiency of the pretreated pulp was similar (∼80%). It is hypothesized that the presence of Al3+ could inhibit the binding of lignin to cellulase, which was supported by the quantum chemistry calculations. Results revealed the presence of cation− π interactions between Al3+ and lignin with interaction energy (ΔE) was 1022.04 kJ/mol and 1003.04 kJ/mol for S and G type of lignin, respectively. In addition, the pretreatment with H2SO4 -AlCl3 co-catalyst could achieve a high lignin removal efficiency of 93.0% and almost complete enzymatic hydrolysis of obtained cellulose pulp (∼100%). This research demonstrated that the co-catalyst strategy effectively improved the overall performance of the solvent-based biorefinery.

CHEMICAL MODIFICATION FOR RESISTANCE TO PHOTO-OXIDATIVE DEGRADATION AND IMPROVED BLEACHING AND COLOR FASTNESS PROPERTIES OF HEMP FIBER

The objective of the research has been to overcome some inherent drawbacks of hemp fiber via chemical modification, which is a vital issue in using it as a textile fiber like cotton. Hemp fiber was modified with treatment liquor (mixture of sulfurous acid and sodium hydroxide) in aqueous medium to remove lignin. The effects of the treatment liquor concentration, fiber to liquor ratio, reaction time and temperature on the percent lignin extracted from hemp fiber were studied. Modified hemp fibers (MHF) were bleached in an alkaline pH aqueous medium with hydrogen peroxide. The process significantly improved lignin removal, bleaching and color fastness. In fact, the whiteness index of bleached MHF was significantly higher than that of bleached raw hemp, but its tensile strength was slightly affected. The photo-oxidative degradation of hemp fiber was 70% lower than that of unmodified (raw) hemp fiber and almost like that of cotton yarn. The color fastness properties of dyed bleached modified hemp fiber were significantly better than those of dyed bleached unmodified hemp fiber and close to those of dyed bleached cotton yarn.

Use of Photo isomers to enhance the removal of lignin from woody biomass hydrolysate: UV irradiated photo isomerization of 4,4-diethoxy-azobenzene enhances precipitation of organosolv lignin from extraction solvents

Conversion of lignocellulose to bioproducts and biofuels is often initiated with a hydrolytic pretreatment process that helps to depolymerize the native polymers in biomass and produce a cellulose rich pulp stream. Extracting dissolved components (lignin) from this hydrolysate is an important step to derive value from the biomass components other than cellulose. In this investigation we propose a novel method to enable precipitation of desired solutes using photo-isomers in the extraction solvent. This photo-switchable solvent enables dissolution or precipitation of desired components using alternating UV or visible light to modify the solubility of the compounds of interest. It was found that among different combinations of three solvents and three photo-isomers, the combination of acetone with 4,4′-diethoxy azobenzene solution was most efficient at precipitating dissolved Organosolv lignin in response to UV light exposure. To our knowledge this is the first demonstration of this approach to separating lignin from organic solvents. This method is significant because it minimizes the high energy demands of traditional lignin extraction methods that involve distillation or large amounts of dilution using antisolvents.

Isolation and characterisation of cellulose nanocrystals from kudzu (Pueraria montana var. lobata): a sustainable packaging material

SummaryFlexible packaging has become indispensable in the food industry due to its numerous advantages. However, it has certain drawbacks, such as limited recyclability and environmental contamination. While efforts are underway to develop more sustainable and eco‐friendly packaging options, the food industry's reliance on flexible packaging made from unsustainable petro‐based plastics is expected to continue in the foreseeable future. Therefore, more sustainable alternatives that do not sacrifice performance are required. One such option is to use nanocellulose, especially cellulose nanocrystals (CNCs), which can be reinforced into biopolymer to enhance mechanical and barrier properties. The present study aims to isolate kudzu CNCs by depolymerisation, bleaching, acid hydrolysis with 51% sulfuric acid, and mechanical dispersion. Thermogravimetric analysis (TGA) was conducted to assess the thermal stability of kudzu fibres. Further, the FTIR spectra were measured at wave number ranged 4000–500 cm−1, which showed changes in the structure after treatments and confirmed the removal of lignin and hemicellulose from the cellulose. The isolated CNCs were found to have lengths and diameters of 285.01 ± 150.33 nm and 42.78 ± 13.26 nm, respectively, with an aspect ratio of 6.43 ± 1.78. This study showed that kudzu CNCs are a suitable reinforcing material for nanocomposites.

Effect of natural deep eutectic solvents on properties of micro crystalline cellulose isolated from kenaf fibre

Natural deep eutectic solvents have gained popularity due to their environmentally benign, recyclable, and reusable properties. They can be used many times without losingtheir effectiveness. Therefore, natural deep eutectic solvents used as effective reagent for lignocellulosic biomass pre-treatment for lignin removal. In this work, the natural deep eutectic solvents (i.e., Lactic Acid: Choline Chloride) is used to treat the kenaf fibre biomass with a molar ratio of 2:1 and then microcrystalline cellulose was obtained through acid hydrolysis. The analytical analysis of kenaf microcrystalline cellulose was investigated through Infrared fourier transform spectroscopy, X-ray Diffraction, thermogravimetric analysis, particle size distribution analysis, and scanning electron microscopy. The fourier transform infrared spectroscopy analysis result showed that the maximum proportion of lignin and partial hemicellulose from kenaf fibre were removed during natural deep eutectic solvents pre-treatment. Kenaf microcrystalline cellulose X-ray diffraction results revealed higher crystallinity at 78° compared to other peaks. The thermal analysis shows the kenaf microcrystalline cellulose thermal stability , making it suitable material for more desirable application in many areas. We concluded from obtained results that microcrystalline cellulose extracted with natural deep eutectic solvent pre-treated kenaf fibre can be used in various cellulosic material development in the future for the food packaging, tissue culture, paper, automotive, biomedical, and pharmaceutical applications.

Greater Importance of Structural Changes Over Lignin Removal in Impacting the Enzymatic Hydrolysis of Crop Straws.

The importance of structural changes and lignin removal in influencing the enzymatic hydrolysis of crop straws was investigated. Alkaline pretreatment of corn stover (CS) and rice straw (RS) was conducted to remove lignin. It was found that alkaline pretreatment caused more lignin removal from CS than RS under the same condition, and CS and RS treated at 40 °C (CS40 and RS40) attained less lignin removal than those treated at 80 °C (CS80 and RS80). However, CS40 achieved glucan conversion efficiency of 70.77% which was 11.85% less than that of RS40, and similar glucan conversion efficiencies were obtained for RS 40 and RS80. Structural observation showed that the connection among single fiber bundle of CS40 was tighter than that of RS40, while those of RS40 and RS80 were loose. It meant that structural changes might be more important than lignin removal to influence enzymatic hydrolysis of crop straws.

Effect of treatment type of natural fibers on the rheological and micromechanical behavior of polyvinyl alcohol composites

AbstractThe viscoelastic and mechanical performance of sustainable raw materials on biodegradable matrices provide insights into how to develop and improve materials that contribute to the circular economy. Thus, we aim to evaluate the effect of conventional (acid or alkali) and dual (alkali/acid‐ultrasound) treatment on Agave fibers, as well as their rheological and micromechanical performance on polyvinyl alcohol (PVA)‐based composites. TGA results indicate that the treatments promote the removal of moisture, waxes, pectin, hemicellulose, and lignin from the fibers to different extents. PVA matrix containing modified fibers exhibits low viscosity, flux index, and critical shear values, indicating a high interaction and dispersion of the filler in the matrix. Furthermore, tensile tests and theoretical predictions of micromechanics‐based finite element analysis show evidence that the modified fiber type provides a different stress transfer ratio () than in the matrix, which changes Young's modulus values. The results indicate that Agave fibers modified by dual treatment are a useful filler to produce soft or stiff PVA composites when looking for potential applications in the mobility industry or other fields like the packaging.

Effect of microwave and ultrasonic irradiation on the enzymatic hydrolysis of water hyacinth biomass in the presence of surfactants

This paper presents the effect of microwave and ultrasound irradiation on the enzymatic hydrolysis of water hyacinth biomass in the presence of surfactants. Prior to hydrolyzing, the water hyacinth was treated utilizing alkali with and without microwave assistance. It was revealed that the microwave improved the removal of lignin and hemicellulose. The treated water hyacinth biomass was also characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), and Fourier-Transform Infrared (FT-IR) Spectroscopy. The effect of surfactant and the assistance of microwave and ultrasound were comprehensively studied. Some parameters varied, including stirring speed, surfactant type, concentration, and reaction time. The results indicated that microwave and ultrasound could enhance the reaction rate. Tween 80 here could improve conventional, microwave-assisted, and ultrasound-assisted hydrolysis of water hyacinth biomass. It was found that the ultrasound-assisted hydrolysis was better than that of others. The results of this research can be used as the groundwork for further developing the lignocellulosic biomass hydrolysis process, especially in an advanced enzymatic hydrolysis process.

Natural arginine-based deep eutectic solvents for rapid microwave-assisted pretreatment on crystalline bamboo cellulose with boosting enzymatic conversion performance

Development of amino acid-based natural deep eutectic solvents (DESs) pretreatment technology on lignocellulosic biomass is a promising approach to biorefinery. In this study, for arginine-based DESs with different molar ratios, the viscosity and Kamlet-Taft solvation parameters were quantified to evaluate the pretreatment performance on bamboo biomass. Further, microwave assisted DES pretreatment was eminent, evidenced by 84.8% lignin removal and increased saccharification yield (from 6.3% to 81.9%) in moso bamboo at 120 °C and ratio of 1:7 (arginine: lactic acid). Results showed degradation of lignin molecules together with release of phenolic hydroxyl units after DESs pretreatment, which is conducive to subsequent utilization. Meanwhile, DES-pretreated cellulose exhibited unique structural characteristics including destroyed crystalline region of cellulose (Crystallinity Index from 67.2% to 53.0%), decreased crystallite size (from 3.41 nm to 3.14 nm) and roughened fiber surface. Thus, arginine-based DES pretreatment has excellent potential in bamboo lignocellulose pretreatment.

Torrefaction on agricultural residues empty fruit bunch: Effect of torrefaction processing factors on thermal properties of torrefied empty fruit bunch biochar

Thermal properties of torrefied empty fruit bunch biochar were investigated in this study as an alternative to be a renewable energy material for future. Holding temperature range between 200 to 300°C and residence time for 30 to 90 minutes were applied as the factors for the torrefaction process. This study observed the thermal properties of torrefied empty fruit bunch biochar by using thermogravimetric analysis (TGA) to study the thermal decomposition before and after torrefaction process. Thermogravimetric analysis was used in identifying those properties, which is dividing into three stages of dehydration, devolatilizations and decomposition of the torrefied biochar. During the dehydration, the moisture content was removed, meanwhile during the second stage (devolatilizations), the volatile matter was removed along with the removal of hemicellulose, cellulose, and lignin, while on the third stage shows the decompositions of the torrefied biochar to completely degrade.

Metal Salt-Based Deep Eutectic Solvent Pretreatment of Moso Bamboo to Improve Enzymatic Hydrolysis

Research on metal salt-based deep eutectic solvent (DES) pretreatment is still in its infancy, and the effect of hydroxyl groups on Cl− in choline chloride (ChCl) is not resolved. In this study, a type IV DES composed of metal salt and glycerol (Gly) was prepared for pretreatment of moso bamboo to improve its enzymatic hydrolysis. The correlation between enzymatic hydrolysis and the contents of hemicelluloses and lignin was evaluated using the Box–Behnken design. The results showed that FeCl3-based DES was optimal among various DES. The solid recovery was reduced to 55.54% following FeCl3/Gly pretreatment, which was effective in the removal of hemicelluloses and lignin compared with ternary DES pretreatment (with ChCl) under mild conditions (100 °C, 3 h). With the increase of pretreatment temperature (120 °C, 2 h), a significant proportion of hemicelluloses (76.07%) and lignin (62.77%) was removed. The structure of FeCl3/Gly pretreatment residue was seriously damaged, and the glucose yield increased to 91.13% following enzymatic hydrolysis. This correlation indicated that the hemicelluloses’ content had a significant influence on enzymatic hydrolysis of the residue following FeCl3/Gly pretreatment. This study elucidates the pretreatment effect of metal salt-based DES, which will be helpful in the value-added conversion of moso bamboo under mild conditions.

Oxidation-driven lignin removal by Agaricus bisporus from wheat straw-based compost at industrial scale

Fungi are main lignin degraders and the edible white button mushroom, Agaricus bisporus, inhabits lignocellulose-rich environments. Previous research hinted at delignification when A. bisporus colonized pre-composted wheat straw-based substrate in an industrial setting, assumed to aid subsequent release of monosaccharides from (hemi-)cellulose to form fruiting bodies. Yet, structural changes and specific quantification of lignin throughout A. bisporus mycelial growth remain largely unresolved. To elucidate A. bisporus routes of delignification, at six timepoints throughout mycelial growth (15 days), substrate was collected, fractionated, and analyzed by quantitative pyrolysis-GC–MS, 2D-HSQC NMR, and SEC. Lignin decrease was highest between day 6 and day 10 and reached in total 42 % (w/w). The substantial delignification was accompanied by extensive structural changes of residual lignin, including increased syringyl to guaiacyl (S/G) ratios, accumulated oxidized moieties, and depleted intact interunit linkages. Hydroxypropiovanillone and hydroxypropiosyringone (HPV/S) subunits accumulated, which are indicative for β-|O-4′ ether cleavage and imply a laccase-driven ligninolysis. We provide compelling evidence that A. bisporus is capable of extensive lignin removal, have obtained insights into mechanisms at play and susceptibilities of various substructures, thus we were contributing to understanding fungal lignin conversion.

Delignification of switchgrass for xylo-oligosaccharides production using sorbic acid hydrolysis

Organic acid as a class of hydrolysis catalysts shows great potential in the production of xylo-oligosaccharides (XOS) from lignocelluloses. However, sorbic acid (SA) hydrolysis for XOS production from lignocellulose has not been reported and it was still unclear how lignin removal affected XOS production. Herein, two factors affecting the XOS production from switchgrass by SA hydrolysis were explored: hydrolysis severity factor (Log R0) and lignin removal. Benefiting from the lignin removal (58.4%) in switchgrass, a desired XOS yield of 50.8% with low by-products was obtained from delignified switchgrass by 3% SA hydrolysis at Log R0 = 3.84. Under these conditions, 92.1% of glucose was obtained by cellulase hydrolysis with Tween 80 addition. From a mass balance perspective, 10.3 g of XOS and 23.7 g of glucose could be produced from 100 g switchgrass. This work proposed a novel strategy for XOS and monosaccharides production from delignified switchgrass.

Valorising Wood Ash as an Effective Green Alternative Pulping Agent for Achieving a High Yield of Banana Micro-Lignocellulose Fibres of Enhanced Crystallinity

AbstractThis study aims to explore the use of wood ash, a common waste, as an alternative and eco-friendly pulping agent. The first and most important singularity of the study is that wood ash solution, though mild in nature, has proven to be an effective pulping agent (in comparison with the common pulping solution, sodium hydroxide): comparable lignin (45%) and hemicellulose (50%) removal, high crystallinity (72–77%) and high pulp yield (70%) were obtained. Another particularity of this study is that the reported advanced aspects of pulped banana fibres, notably the chemical functionality, crystallinity and crystallite size have been correlated with the chemical composition of the wood ash used: calcium pectinate was formed on the pulped fibre surface. It apparently played a role in enhancing the fibre crystallinity. Moreover, another specialness of this study is that non-conventional factors, which would have significant bearing during industrial scale processing, such as liquor ratio, fibre input size and duration have been investigated—the latter has shown that to attain maximum delignification, small fibre input size at a high liquor ratio of 40 for an extended period of 2 h are necessary. Finally, the pulped banana fibres (which were intended to be used for membrane fabrication for use in water purification system) have depicted their applicability in the fabrication of ultrafiltration membranes by virtue of their aspect ratio, semi-hydrophilicity (due to presence of residual lignin) and projected high mechanical strength (due to high crystallinity and low crystallite size). Graphical Abstract Graphical abstract showing outcomes when pulping with wood ash solution.