Lignocellulosic Pretreatment Research Articles

Combination of pH adjusting and intermittent feeding can improve fermentative acetone-butanol-ethanol (ABE) production from steam exploded corn stover

Steam explosion (SE) is an effective and industrially scalable lignocellulose pretreatment method that can be used for second-generation acetone-butanol-ethanol (ABE) fermentation. Nevertheless, a series technical barrier including the high inhibitors content in hydrolysate, and low concentration and low yield of ABE production always hindered the availability of the SE technique. In this study, aiming to solve the above obstacles and boosting cellulosic ABE production, the ABE fermentation process was intensified by a novel fed-batch strategy that combined the pH adjusting with intermittent feeding. Results revealed that maintaining the pH at 6.5 for initial 12 h of cultivation ensures the smoothly shifting of the acidogenesis phase to solventogenesis phase of the C. acetobutylicum cells, so that avoided the acid crash. While the lag period of fermentation was obvious shorted by intermittent feeding the concentrated SE hydrolysate into the dilute broth. Consequentially, 17.75 g/L of ABE (containing 11.75 g/L of butanol) can be obtained after 48 h of inoculation, with the yield and productivity of ABE were 0.36 g/g (of sugars) and 0.37 g/L‧h, respectively. Correspondingly, 194.9 g of ABE (including 129.0 g of butanol) can be produced from 1 kg of dried corn stover. Therefore, the novel process intensifying method could obviously improve the biobutanol production, which showed high potential and applicability in large-scale ABE productions.

1-Butyl-3-methylimidazolium acetate pretreatment of giant reed triggering yield improvement of biohydrogen production via photo-fermentation

Ionic liquids (ILs) have been considered as promising alternatives to traditional reagent for lignocellulosic biomass pretreatment because of their tunable physicochemical and “green” properties. In the study, the influence of 1-Butyl-3-methylimidazolium acetate ([Bmim]acetate) pretreatment of giant reed on H2 yield improvement via photo-fermentation (PF) was evaluated. Under the optimal pretreatment conditions (6 g/L [Bmim]acetate at 70 °C for 4 h), the delignification of giant reed was up to 26.7 %. In addition, the sugar yield (9.5 g/L) and hydrogen yield (72.3 mL/g TS) from giant reed were enhanced by 1.7-fold and 61.7 % over those of untreated giant reed, respectively. Moreover, ternary analysis showed that retention time had the strongest effect on delignification, sugar yield and hydrogen yield of giant reed compared to pretreatment temperature and [Bmim]acetate loading. These experimental results indicated that [Bmim]acetate pretreatment of giant reed is an effective approach to enhance the hydrogen yield via PF.

Optimisation of Rice Husks’ Lignocellulose Pre-Treatment Methods and Use of Central Composite Design in Citric Acid Fermentation: A Review

In today’s industry, about 80% to 90% of citric acid (C6H8O7) production is carried out using submerged fermentation method and Aspergillus niger as citric acid producing microorganism. The use of fermentation method provides advantages, including the utilization of agricultural waste as substrate. Rice husks can be used as substrate in citric acid fermentation because they contain high cellulose and hemicellulose. However, agricultural waste also contains lignin which can interfere with the hydrolysis of cellulose and hemicellulose into reducing sugars, therefore optimisation of pre-treatment process is needed to separate lignin in rice husk. In addition to the optimisation of pre-treatment process, optimisation of fermentation parameter variations to obtain maximum citric acid yield is necessary. Therefore, the aim of this narrative review is to desribe various pre-treatment methods that can be done to remove lignin from rice husks, and to provide information on the benefits of using the Central Composite Design method in the optimisation of various fermentation parameters.

Recent Advances in the Bioconversion of Waste Straw Biomass with Steam Explosion Technique: A Comprehensive Review

Waste straw biomass is an abundant renewable bioresource raw material on Earth. Its stubborn wooden cellulose structure limits straw lignocellulose bioconversion into value-added products (e.g., biofuel, chemicals, and agricultural products). Compared to physicochemical and other preprocessing techniques, the steam explosion method, as a kind of hydrothermal method, was considered as a practical, eco-friendly, and cost-effective method to overcome the above-mentioned barriers during straw lignocellulose bioconversion. Steam explosion pretreatment of straw lignocellulose can effectively improve the conversion efficiency of producing biofuels and value-added chemicals and is expected to replace fossil fuels and partially replace traditional chemical fertilizers. Although the principles of steam explosion destruction of lignocellulosic structures for bioconversion to liquid fuels and producing solid biofuel were well known, applications of steam explosion in productions of value-added chemicals, organic fertilizers, biogas, etc. were less identified. Therefore, this review provides insights into advanced methods of utilizing steam explosion for straw biomass conversion as well as their corresponding processes and mechanisms. Finally, the current limitations and prospects of straw biomass conversion with steam explosion technology were elucidated.

Lignocellulose dissociation with biological pretreatment towards the biochemical platform: A review.

Lignocellulose utilization has been gaining great attention worldwide due to its abundance, accessibility, renewability and recyclability. Destruction and dissociation of the cross-linked, hierarchical structure within cellulose hemicellulose and lignin is the key procedure during chemical utilization of lignocellulose. Of the pretreatments, biological treatment, which can effectively target the complex structures, is attractive due to its mild reaction conditions and environmentally friendly characteristics. Herein, we report a comprehensive review of the current biological pretreatments for lignocellulose dissociation and their corresponding degradation mechanisms. Firstly, we analyze the layered, hierarchical structure of cell wall, and the cross-linked network between cellulose, hemicellulose and lignin, then highlight that the cracking of β-aryl ether is considered the key to lignin degradation because of its dominant position. Secondly, we explore the effect of biological pretreatments, such as fungi, bacteria, microbial consortium, and enzymes, on substrate structure and degradation efficiency. Additionally, combining biological pretreatment with other methods (chemical methods and catalytic materials) may reduce the time necessary for the whole process, which also help to strengthen the lignocellulose dissociation efficiency. Thirdly, we summarize the related applications of lignocellulose, such as fuel production, chemicals platform, and bio-pulping, which could effectively alleviate the energy pressure through bioconversion into high value-added products. Based on reviewing of current progress of lignocellulose pretreatment, the challenges and future prospects are emphasized. Genetic engineering and other technologies to modify strains or enzymes for improved biotransformation efficiency will be the focus of future research.

Peroxyacetic Acid Pretreatment: A Potentially Promising Strategy towards Lignocellulose Biorefinery.

The stubborn and complex structure of lignocellulose hinders the valorization of each component of cellulose, hemicellulose, and lignin in the biorefinery industries. Therefore, efficient pretreatment is an essential and prerequisite step for lignocellulose biorefinery. Recently, a considerable number of studies have focused on peroxyacetic acid (PAA) pretreatment in lignocellulose fractionation and some breakthroughs have been achieved in recent decades. In this article, we aim to highlight the challenges of PAA pretreatment and propose a roadmap towards lignocellulose fractionation by PAA for future research. As a novel promising pretreatment method towards lignocellulosic fractionation, PAA is a strong oxidizing agent that can selectively remove lignin and hemicellulose from lignocellulose, retaining intact cellulose for downstream upgrading. PAA in lignocellulose pretreatment can be divided into commercial PAA, chemical activation PAA, and enzymatic in-situ generation of PAA. Each PAA for lignocellulose fractionation shows its own advantages and disadvantages. To meet the theme of green chemistry, enzymatic in-situ generation of PAA has aroused a great deal of enthusiasm in lignocellulose fractionation. Furthermore, mass balance and techno-economic analyses are discussed in order to evaluate the feasibility of PAA pretreatment in lignocellulose fractionation. Ultimately, some perspectives and opportunities are proposed to address the existing limitations in PAA pretreatment towards biomass biorefinery valorization. In summary, from the views of green chemistry, enzymatic in-situ generation of PAA will become a cutting-edge topic research in the lignocellulose fractionation in future.

Agarase, Amylase and Xylanase from Halomonas meridiana: A Study on Optimization of Coproduction for Biomass Saccharification

Coproduction of multienzymes from single potential microbe has captivated contemplation in industries. Bacterial strain, Halomonas meridiana VITSVRP14, isolated from seaweed was labored to produce amylase, agarase and xylanase conjointly using submerged fermentation. The optimum production conditions clinched by classical optimization were: pH 8; 1.5% inoculum; 24 h incubation, 40 °C; 8% NaCl (sodium chloride); 1% lactose and NaNO3 (sodium nitrate). The preponderant variables (pH, temperature, lactose) and their interaction effect on enzyme production were studied by Plackett-Burman design and Response Surface Methodology (RSM). There were 3.29, 1.81 and 2.08 fold increase in enzyme activity with respect to agarase, amylase and xylanase after optimization against basal medium. After 24 h of enzymatic treatment, the saccharification rates of the coproduced enzyme mixture were 38.96% on rice bran, 49.85% on wheat bran, 61.2% on cassava bagasse and 57.82% on corn cob. Thus, the coproduced enzyme mixture from a bacterium with halotolerance is plausible in pretreated lignocellulose degradation. The ability of this single microbe Halomonas meridiana VITSVRP14, in coproducing agarase, amylase and xylanase give the nod for its application in biomass saccharification by subsiding cost, energy and time involved in the process.

A consolidated review of commercial-scale high-value products from lignocellulosic biomass.

For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.

Ultrasonic-assisted fungi modification of lignocellulose-derived hierarchical porous carbon for efficient desalination

Biomass materials have received increasing attention due to their eco-friendly, high availability and low costs. However, these biomass materials have stubborn structural characteristics, which require specific pretreatment methods to promote practical value. Herein, we reported a novel strategy of ultrasonic-fungi pretreatment of lignocellulose to obtain biomass-based hierarchical porous carbon (LSC-FU). The structure of LSC-FU enables the fabricated electrode to exhibit high conductivity and rapid ion transport properties, with capacitance retention of 99.7 % after 5000 consecutive cycles. And it shows a high adsorption capacity (500 mg·L−1) of 29.39 mg·g−1 with a 94.6 % adsorption capacity retention rate in the electrosorption test. The lignocellulose-based porous carbon electrodes obtained by this effective pretreatment method have great potential for the practical application of CDI. This work provides original outlooks to prepare high-performance carbon electrodes. It emphasizes the significance of sustainable development and green environmental protection by using natural biomass materials to prepare porous carbon materials.

Improvement of cell-tethered cellulase activity in recombinant strains of Saccharomyces cerevisiae.

Consolidated bioprocessing (CBP) remains an attractive option for the production of commodity products from pretreated lignocellulose if a process-suitable organism can be engineered. The yeast Saccharomyces cerevisiae requires engineered cellulolytic activity to enable its use in CBP production of second-generation (2G) bioethanol. A promising strategy for heterologous cellulase production in yeast entails displaying enzymes on the cell surface by means of glycosylphosphatidylinositol (GPI) anchors. While strains producing a core set of cell-adhered cellulases that enabled crystalline cellulose hydrolysis have been created, secreted levels of enzyme were insufficient for complete cellulose hydrolysis. In fact, all reported recombinant yeast CBP candidates must overcome the drawback of generally low secretion titers. Rational strain engineering can be applied to enhance the secretion phenotype. This study aimed to improve the amount of cell-adhered cellulase activities of recombinant S. cerevisiae strains expressing a core set of four cellulases, through overexpression of genes that were previously shown to enhance cellulase secretion. Results showed significant increases in cellulolytic activity for all cell-adhered cellulase enzyme types. Cell-adhered cellobiohydrolase activity was improved by up to 101%, β-glucosidase activity by up to 99%, and endoglucanase activity by up to 231%. Improved hydrolysis of crystalline cellulose of up to 186% and improved ethanol yields from this substrate of 40-50% in different strain backgrounds were also observed. In addition, improvement in resistance to fermentation stressors was noted in some strains. These strains represent a step towards more efficient organisms for use in 2G biofuel production. KEY POINTS: • Cell-surface-adhered cellulase activity was improved in strains engineered for CBP. • Levels of improvement of activity were strain and enzyme dependent. • Crystalline cellulose conversion to ethanol could be improved up to 50%.

CRISPR/Cas9 using a transient transformation system in Ceriporiopsis subvermispora.

Ceriporiopsis subvermispora is a white-rot fungus with great potential for industrial and biotechnological applications, such as the pretreatment of lignocellulose in biorefineries, as it decomposes the lignin in the plant cell wall without causing severe cellulose degradation. A genetic transformation system was recently developed; however, gene-targeting experiments to disrupt or modify the gene(s) of interest remain challenging, and this is a bottleneck for further molecular genetic studies and breeding of C. subvermispora. Herein, we report efficient clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9)-assisted gene mutagenesis in this fungus. Two plasmids expressing Cas9 together with a different pyrG-targeting single-guide RNA were separately introduced into the monokaryotic C. subvermispora strain FP-90031-Sp/1, which frequently generated strains that exhibited resistance to 5-fluoroorotic acid and uridine/uracil auxotrophy. Southern blot analyses and genomic polymerase chain reaction followed by DNA sequencing of some mutants revealed that they were pyrG mutants. We also observed that hygromycin resistance of the pyrG mutants was frequently lost after repeated subcultivations, indicating that a maker-free genome editing occurred successfully. It is also suggested that a gene mutation(s) can be introduced via a transient expression of Cas9 and a single-guide RNA; this feature, together with high-frequency gene targeting using the CRISPR/Cas9 system, would be helpful for studies on lignocellulose-degrading systems in C. subvermispora. KEY POINTS: • Efficient plasmid-based CRISPR/Cas9 was established in C. subvermispora. • The mutations can be introduced via a transient expression of Cas9 and sgRNA. • A maker-free CRISPR/Cas9 is established in this fungus.

Cellulose Nanofiber Preparation Combined with Bioethanol Production from Fermented Sweet Sorghum Bagasse

In order to achieve cost-competitive industrial production of cellulose nanofibers (CNFs), bioethanol extraction and lignocellulose pretreatment from fermented sweet sorghum bagasse were combined with alkaline distillation in this study. CNFs were further prepared from an alkaline-distilled substrate after washing, bleaching, and a high-pressure homogenization process. Lignin-containing cellulose nanofibers (LCNFs) were simultaneously prepared without bleaching. The effects of different alkali loadings on the ethanol quality and performances of CNFs and LCNFs were investigated. Results showed that only 12.94 mg/L of alkali residue was found in extracted ethanol at the highest alkali dosage, which can be removed in the subsequent purification process. Cellulose fibers can be prepared from sweet sorghum bagasse during alkaline distillation, and the crystallinity of pretreated samples increased from 37.2 to 59.5%. It is observed by transmission electron microscopy that the obtained nanofibrils aggregated and formed a network in suspension. The degradation temperature of the CNFs can be increased up to 352 °C, which is 34 °C higher than that of LCNFs due to less hemicellulose content. Wastewater was only generated in the washing process during alkali distillation, which is far less than that generated in a conventional pulping making process. The process scale-up simulation indicates that the coproduction of bioethanol and CNFs or LCNFs by alkaline distillation is environment-friendly and energy-efficient for industrialization.

Revisiting Theoretical Tools and Approaches for the Valorization of Recalcitrant Lignocellulosic Biomass to Value-Added Chemicals

Biorefinery processes for converting lignocellulosic biomass to fuels and chemicals proceed via an integrated series of steps. Biomass is first pretreated and deconstructed using chemical catalysts and/or enzymes to liberate sugar monomers and lignin fragments. Deconstruction is followed by a conversion step in which engineered host organisms assimilate the released sugar monomers and lignin fragments, and produce value-added fuels and chemicals. Over the past couple of decades, a significant amount of work has been done to develop innovative biomass deconstruction and conversion processes that efficiently solubilize biomass, separate lignin from the biomass, maximize yields of bioavailable sugars and lignin fragments and convert the majority of these carbon sources into fuels, commodity chemicals, and materials. Herein, we advocate that advanced in silico approaches provide a theoretical framework for developing efficient processes for lignocellulosic biomass valorization and maximizing yields of sugars and lignin fragments during deconstruction and fuel and chemical titers during conversion. This manuscript surveys the latest developments in lignocellulosic biomass valorization with special attention given to highlighting computational approaches used in process optimization for lignocellulose pretreatment; enzyme engineering for enhanced saccharification and delignification; and prediction of the genome modification necessary for desired pathway fine-tuning to upgrade products from biomass deconstruction into value-added products. Physics-based modeling approaches such as density functional theory calculations and molecular dynamics simulations have been most impactful in studies aimed at exploring the molecular level details of solvent-biomass interactions, reaction mechanisms occurring in biomass-solvent systems, and the catalytic mechanisms and engineering of enzymes involved in biomass degradation. More recently, with ever increasing amounts of data from, for example, advanced mutli-omics experiments, machine learning approaches have begun to make important contributions in synthetic biology and optimization of metabolic pathways for production of biofuels and chemicals.

Molecular interaction between ionic liquids with lignin dimers

Biomass is an alternative to using fossil fuels. It is made up mainly of agricultural and forestry residues. The main components of biomass are cellulose, hemicellulose, and lignocellulose (Li, 2015). Due to the structure of lignin and its chemical properties, chemical products based on aromatic compounds and fuels can be obtained (Sangha, 2012). However, its recalcitrant nature and the difficulties encountered in effecting depolymerization, coupled with its low solubility with common organic solvents, result in conversion processes that use extreme conditions of temperature, pressure and acidity (Hicks, 2011). Ionic liquids (ILs) are advantageous solvents for the conversion of lignin to a value-added product due to their ease of dissolving it. In this work we studied the interaction of nine different ILs, formed between the [EMIM+], [BMIM+] y [HMIM+] and the anions [BF4-], [OAc-] and [Cl-], whose use has been reported in the industrial pretreatment of lignocellulose (For, 2007), and lignin dimersderived from coniferyl alcohol (one of the basic units of lignin), which contain the characteristic β-O-4 bond of the biopolymer. Born-Oppenheimer (DMBO) quantum molecular dynamics calculations were performed with the BIOVIA 2016 Materials Studio program (BIOVIA, Dassault Systèmes, 2017), varying the pressure and temperature conditions with the micro canonical assemblies NVE and NVT. The results obtained with the NVE and NVT assemblies show that for some LIs the interaction is favorable and for others there is a great destabilization of the Lignin-IL interaction.

Unveiling the Migration and Transformation Mechanism of Lignin in Eucalyptus During Deep Eutectic Solvent Pretreatment.

Deep eutectic solvents (DESs) have unique advantages in biomass conversion. However, the migration and transformation mechanism of lignin in the cell wall during the DES pretreatment is still elusive. In this work, Eucalyptus blocks were pretreated in choline chloride/lactic acid DES to reveal the lignin migration. Meanwhile, the remaining lignin in the pretreated residue, the regenerated DES lignin, and the solubilized degraded lignin in the recovered DES were investigated to decipher the lignin transformation. Results showed that the DES pretreatment resulted in the penetration of DES from the cell lumen to the cell wall, and lignin in the secondary wall was more easily dissolved than that in the cell corner middle lamella. The syringyl unit of lignin was better stabilized in the DES than the guaiacyl unit of lignin. The condensed lignin fraction mainly remained in the pretreated residue, while the solubilized degraded lignin fraction was monomeric aromatic ketone compounds. This study elucidates the fate of lignin during the DES pretreatment, which could also promote the development of a modern lignocellulosic pretreatment technique.

Delignification of oil palm empty fruit bunch under mild conditions by air oxygen and manganese gluconate

The oil palm empty fruit bunch (OPEFB) as a lignocellulosic material is available abundantly in Indonesia, because this country is one of the world's largest producer of crude palm oil. Pre-treatment of lignocellulosic biomass is a necessary step to break the lignin and hemicellulose structure and makes polysaccharides easily available for enzyme digestion. The aim of this study was to evaluate the performance of lignocellulose pre-treatment with air oxygen catalysed by manganese gluconate complex at temperatures below 343 K and pH of 8–9.5. Delignification experiments were carried out in a reactor flask which equipped with a heater, stirrer, reflux condenser, thermometer, and air injection channel. The optimum delignification results based on kappa number values were around 93 at pH of 8.5 for 4 hours, and temperature of 338 K, mass ratio Mn2+ to OPEFB (%) of 0.33, volume soaking solution of 125 ml, molar ratio gluconic acid/Mn2+ of 15:1 and air flow rate of 460 ml/min. It was shown that delignification by manganese gluconate with oxygen air under atmospheric conditions is very promising because can reduce energy consumption and ensure environmental safety. The value of kappa number was still high, but very interesting for further study because it operates at mild condition and uses green chemicals such as gluconic acid and oxygen air.

The correlation between the physicochemical properties and enzymatic hydrolyzability of hydrothermal pretreated wheat straw: A quantitative analysis

Hydrothermal pretreatment with diluted acid or alkali can disrupt the compact structure of wheat straw at a moderate temperature for efficient enzymatic saccharification. However, the quantitative analysis between the physicochemical properties and enzymatic hydrolyzability of hydrothermal pretreated lignocellulose was rarely investigated, which hindered the development of model-based applications for process design and control. Herein, correlation analysis (CA) and principal component analysis (PCA) were conducted to elucidate the dominant factors affecting the enzymatic hydrolyzability and quantitative relationship between them. CA results suggested the major positive factor affecting carbohydrate conversion was cellulose content (r = 0.86). Through logarithmic processing and linear combination, these intercorrelated factors were successfully converted into two newly uncorrelated variables named the first principal component (PC1) and the second principal component (PC2). The initial hydrolysis rate and carbohydrate conversion can be well predicted by PC1 and PC2 scores through multiple linear regression with a high R-squared (0.91 and 0.80).

A systematic study of lignocellulose nanofibrils (LCNF) prepared from wheat straw by varied acid pretreatments

Due to the complex and recalcitrant structure of the cell wall, the current process of lignocellulose nanofibrils (LCNF) preparation directly from lignocellulosic biomass presents environmental pollution, large consumption of energy and chemicals, and low economic efficiency. In the previous research, we successfully prepared LCNF from wheat straw. However, the mechanism of different acids with small quantities in the pretreatment of lignocellulose during the preparation of LCNF is unrevealed. Herein, we select six organic and inorganic acids to pretreat wheat straw combined with glycerol swelling and mechanical action to directly prepare LCNF from wheat straw. The chemical, physical, mechanical, and thermal performances of LCNF are systematically investigated. Furthermore, the acidity of different reaction systems (glycerol and glycerol mixture containing varied acids) is evaluated to reveal the potential relationship between the performance of LCNF and varied acids with small quantities. The obtained H2SO4-LCNF film possesses good mechanical performances (the specific tensile stress of 78.4 KN m/kg and specific Young's modulus of 6.0 MN m/kg). Overall, we hope this work could offer theoretical guidance for the large-scale production of LCNF directly from lignocellulosic biomass by varied acid pretreatments.

Pretreatment of Corn Stover by Levulinic Acid-Based Protic Ionic Liquids for Enhanced Enzymatic Hydrolysis

Economically competitive and sustainable dissolution pretreatment technology is in high demand due to the remarkable achievement in the pretreatment of lignocellulose using ionic liquids (ILs) for enhanced enzymatic hydrolysis. Herein, levulinic acid (Lev), a well-known bio-based platform chemical derived from carbohydrates, in conjunction with a series of organic superbases, was used as a raw chemical to prepare a new class of protic ILs (PILs). The findings indicated that the obtained PILs exhibited a good solubility of up to 10 wt % toward corn stover-based lignocellulose at 140 °C in 40 mins, based on which a facile and efficient dissolution pretreatment technology was developed for enhanced enzymatic hydrolysis of corn stover. The facile dissolution and regeneration of corn stover resulted in significant changes in the composition and physical–chemical structures. These changes led to significantly enhanced enzymatic hydrolysis behavior of the pretreated sample with total reducing sugar and glucose yields of 0.8 and 0.49 g/g within 48 h under optimal conditions, respectively. The Kamlet–Taft solvent parameters of the PILs were systematically evaluated, and the interaction between the lignocellulose and PILs was studied by 13C NMR, indicating that the satisfactory performance of PILs was benefited from the higher ß parameter value and the stronger interactions, particularly the existence of the extra hydrogen-bond interaction from the potential keto–enol tautomerism of the ketone groups in levulinate anions. The compositional and physicochemical changes in the lignocellulose were systematically evaluated to achieve an in-depth understanding of the dissolution activation mechanism using various characterization techniques. The findings also showed that 44.3% of lignin could be fractionated during the facile dissolution and regeneration process, together with a transformation of the crystalline structure of cellulose I to cellulose II and of the packed morphology to a porous one. The structure of the fractionated lignin was also characterized for a better understanding of the fractionation process. The study demonstrated a new sustainable dissolution pretreatment technology for enhanced enzymatic hydrolysis, which can provide significant insights into the design of new solvents for biomass dissolution and processing.

Tailoring the properties of nanocellulose-sepiolite hybrid nanopapers by varying the nanocellulose type and clay content

The development of nanocellulose-clay materials resulted of great relevance, as it opened up the applications of nanocellulose, but it still requires new approaches that could contribute to improve the preparation procedures and the features of this type of biohybrid materials. In this context, nanocellulose-sepiolite (NC-S) biocomposite foams and films have already been successfully tested for some applications. However, the influence of the nanocellulose properties on sepiolite-cellulose interactions, and consequently on the final properties and potential applications of NC-S biohybrid materials, has not been previously studied. To address this knowledge gap, four kinds of nanocelluloses produced from elm biomass (non-chemically pretreated lignocellulose and bleached cellulose nanofibers (LCNFs and CNFs, respectively), TEMPO-oxidized cellulose nanofibers (TOCNFs) and cellulose nanocrystals (CNCs)) were characterized and used to develop NC-S nanopapers. A stronger interaction was found between sepiolite and negatively charged nanocelluloses (TOCNFs and CNCs), improving their thermal stability and mechanical properties by increasing the sepiolite content. Furthermore, the type of nanocellulose and the sepiolite content could be adjusted to tune the flammability, water permeability and mechanical and optical properties of the NC-S nanopapers.Graphical abstract