Restructuring the Crystalline Cellulose Hydrogen Bond Network Enhances Its Depolymerization Rate

The center for nonlinear studies: A personal history

The Center for Nonlinear Studies (CNLS) was an integral part of my scientific career starting as a Postdoctoral Fellow in 1983 up to my tenure as CNLS Director from 2004 to 2015. As such, I experienced a number of scientific phases of CNLS through almost four decades of foundation, evolution, and transition. Throughout this entire interval, the inspiration and influence of David Campbell guided my way. A proper history of CNLS encompassing all of the many contributors to the CNLS story is beyond my means or purpose here. Instead, I present the history as I experienced it. I emphasize the main scientific accomplishments achieved at CNLS over more than 40 years, but I will also attempt to describe and quantify the attributes that made and continue to make the Center for Nonlinear Studies a special institution of remarkable impact and longevity. Throughout its existence, CNLS owes much to the enduring legacy of David Campbell who laid down the foundations and operating principles that have made it so successful.

Eco-friendly preparation and characterization of high-performance electrothermal graphene-AgNPs/lignocellulose composites

Graphene-based (Gr-based) electrothermal heaters, due to their light weight, low electrical resistance, high thermal conductivity, and easy accessibility, have attracted widespread attention in the field of electrothermal heating. To achieve a high steady-state temperature in electrothermal heaters under low voltage, here we constructed a Gr-based film with low electrical resistance. Firstly, we employed non-toxic vitamin C to reduce silver nitrate for the in situ chemical deposition of silver nanoparticles (AgNPs) on the Gr surface. The SEM results confirmed that the AgNPs were uniformly deposited on the Gr surface. The synergistic interaction between AgNPs and Gr provided high-speed electrons transport paths for the film. On the other hand, we employed biodegradable lignocellulose fiber (LCF) as a dispersant and film-forming agent. The aromatic ring structure of LCF interacts with Gr via π-π interactions, aiding the dispersion of Gr in aqueous solutions. SEM results revealed that LCF permeated through the surfaces and interstices of the two-dimensional Gr sheets, providing mechanical support for the composite film. This approach enables the creation of freestanding Gr-AgNPs/LCF electrothermal composites. The resistivity and electrothermal results demonstrated that the obtained 20 wt% Gr-based composite film possessed low electrical resistance (5.4 Ω sq-1) and exhibited an outstanding saturated temperature of 214 °C under a very low input voltage of 7 V. The preparation method of this Gr-based composite film is simple, easy to operate, and environmentally friendly, providing a new reference for the preparation of eco-friendly and high-performance resistance heating electronics.

Cellulose modification for sustainable polymers: overcoming problems of solubility and processing

Two new water-soluble cellulose derivatives were prepared by a two-step transformation with 1,3-propane sultone, followed by either maleic or succinic anhydride, thereby converting cellulose into a more easily processable form. It was found that the solubility was dependent on both the degree of substitution and the chemical properties of the substituents. The water-soluble cellulose has a molecular weight greater than 100 000 g mol-1 and both the morphology and molecular weight can be tuned by varying the reaction conditions. Furthermore, the flexible, two-step nature of the process allows for expansion of this methodology in order to prepare cellulose analogues for different applications.

A flavonol-labelled cellulose fluorescent probe combined with composite fluorescent film imaging and smartphone technology for the detection of Fe3

Fe3+ is one of the most widely distributed and abundant elements on earth. Realizing efficient and real-time monitoring of Fe3+ is of great significance for the natural environment and the health of living organisms. In this paper, a flavonol-labelled cellulose-based fluorescent probe (ACHM) was synthesized by using dialdehyde cellulose (DAC) as the backbone and combining with flavonol derivatives (AHM - 1). The mechanism of recognizing Fe3+ was verified by characterizing the structure of ACHM by NMR, HRMS (High Resolution Mass Spectrometry), FTIR (Fourier Transform Infrared Spectroscopy), XRD (X-ray Diffraction), TG (Thermogravimetry) and SEM (Scanning Electron Microscopy). The H2O solution of the probe ACHM showed good fluorescence properties. It has quenching fluorescence properties for Fe3+, with a low limit of detection (LOD) of 0.10 μM and a fast response time of only 20 s. In addition, in order to expand the application range of the probe, ACHM was prepared as a fluorescent composite film with an average tensile strength of 32.9 MPa and an average elongation at break of 3.39 %. It shows its superiority in mechanical properties. The probe also demonstrated its practical application value for detecting Fe3+ in smartphone imaging applications.

Supercharging carbohydrate-binding module alone enhances endocellulase thermostability, binding, and activity on cellulosic biomass

Lignocellulosic biomass recalcitrance to enzymatic degradation necessitates high enzyme loadings incurring large processing costs for industrial-scale biofuels or biochemicals production. Manipulating surface charge interactions to minimize non-productive interactions between cellulolytic enzymes and plant cell wall components (e.g., lignin or cellulose) via protein supercharging has been hypothesized to improve biomass biodegradability, but with limited demonstrated success to date. Here we characterize the effect of introducing non-natural enzyme surface mutations and net charge on cellulosic biomass hydrolysis activity by designing a library of supercharged family-5 endoglucanase Cel5A and its native family-2a carbohydrate binding module (CBM) originally belonging to an industrially relevant thermophilic microbe Thermobifida fusca . A combinatorial library of 33 mutant constructs containing different CBM and Cel5A designs spanning a net charge range of -52 to 37 was computationally designed using Rosetta macromolecular modelling software. Activity for all mutants was rapidly characterized as soluble cell lysates and promising mutants (containing mutations either on the CBM, Cel5A catalytic domain, or both CBM and Cel5A domains) were then purified and systematically characterized. Surprisingly, often endocellulases with mutations on the CBM domain alone resulted in improved activity on cellulosic biomass, with three top-performing supercharged CBM mutants exhibiting between 2-5-fold increase in activity, compared to native enzyme, on both pretreated biomass enriched in lignin (i.e., corn stover) and isolated crystalline/amorphous cellulose. Furthermore, we were able to clearly demonstrate that endocellulase net charge can be selectively fine-tuned using protein supercharging protocol for targeting distinct substrates and maximizing biocatalytic activity. Additionally, several supercharged CBM containing endocellulases exhibited a 5-10 °C increase in optimal hydrolysis temperature, compared to native enzyme, which enabled further increase in hydrolytic yield at higher operational reaction temperatures. This study demonstrates the first successful implementation of enzyme supercharging of cellulolytic enzymes to increase hydrolytic activity towards complex lignocellulosic biomass derived substrates.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

Aqueous-Cellulose-Solvent-Derived Changes in Cellulose Nanocrystal Structure and Reinforcing Effects

Cellulose nanocrystals as reinforcing agents have received considerable interest, and their dimension mainly depends on the original sources of cellulose. We intend to manually modulate the morphology of cellulose nanocrystals by treating them with cellulose solvents so that we can explore their reinforcing capacity. In this work, waste cotton fabric was processed in two aqueous solvents (a sulfuric acid aqueous solution and a NaOH/urea aqueous solution), and the regenerated cellulose was used to produce cellulose nanocrystals using acid hydrolysis. The results revealed that the nanocrystals (RCNC-H) obtained after the treatment in sulfuric acid had a hybrid crystalline structure and a needle-like shape with an aspect ratio of about 15.2, while cotton fabric was completely dissolved in the NaOH/urea aqueous solution, and the regenerated nanocrystals (RCNC-N) displayed a typical crystalline form of cellulose II with a higher crystallinity and a shorter rod-like shape with an aspect ratio of about 6.3. The reinforcing effects of RCNC-H and RCNC-N were evaluated using polyvinyl alcohol (PVA) films as a model, where the addition of RCNC-H resulted in a relatively better tensile strength and oxygen barrier property, and the PVA/RCNC-N films had a slightly lower water vapor permeability. Therefore, this work suggests a new possibility for altering the naturally formed nanostructure of cellulose for different applications.

Extended Ensemble Molecular Dynamics Study of Ammonia-Cellulose I Complex Crystal Models: Free-Energy Landscape and Atomistic Pictures of Ammonia Diffusion in the Crystalline Phase

Here, we report extended ensemble molecular dynamics simulations of ammonia-cellulose I complex crystal models to evaluate the diffusion behavior of the guest ammonia molecules and the potential of mean force (PMF), namely, the free energy change along the chosen reaction coordinate, for migration of an ammonia molecule in the crystal models. Accelerated molecular dynamics simulations confirmed that ammonia molecules almost exclusively diffused through the hydrophilic channel even when the crystal framework was retained. Adaptive steered molecular dynamics simulations detected distinct PMF peaks with heights of approximately 7 kcal/mol as the ammonia molecule passed through the cellulose-chain layers. Introducing hybrid quantum mechanical and molecular mechanics theory to the adaptive steered molecular dynamics simulation effectively lowered the heights of the PMF peaks to approximately 5 kcal/mol, accompanied by a slight decrease in the baseline. Removal of the ammonia molecules in the neighboring channels resulted in a continuous increase in the baseline for the migration of an ammonia molecule in the hydrophilic channel. When the halves of the crystal model were separated to widen the hydrophilic channel to 0.2 nm, the PMF profiles exhibited an unexpected increase. This resulted from water structuring in the expanded hydrophilic channel, which disappeared with further expansion of the hydrophilic channel to 0.3 nm.

The crystalline structure transition and hydrogen bonds shift determining enhanced enzymatic digestibility of cellulose treated by ultrasonication

Global energy issue raised the necessity to develop second-generation biofuels, and biorefinery of cellulosic biomass becomes a promising solution. Various pretreatments were used to overcome the cellulose nature of recalcitrance and improve the enzymatic digestibility, but the lack of mechanism understanding hindered the development of efficient and cost-effective technologies of cellulose utilization. Using structure-based analysis, we demonstrate that the improved hydrolysis efficiency caused by ultrasonication was ascribed to the changed cellulose properties rather than the increased dissolubility. Further, isothermal titration calorimetry (ITC) analysis suggested that enzymatic digestion of cellulose is an entropically favored reaction driven by hydrophobic forces other than an enthalpically favored reaction. The changes in cellulose properties and thermodynamic paramenters due to ultrasonication accounted for the improved accessibility. Ultrasonication-treated cellulose showed porous, rough and disordered morphology, accompanying with the loss of crystalline structure. Despite the unaffected unit cell structure, ultrasonication expanded the crystalline lattice by increasing grain sizes and average cross-sectional area, resulting in the transformation from cellulose I to cellulose II, with the decreased crystallinity, better hydrophilicity and increased enzymatic bioaccessibility. Furthermore, FTIR combined with two-dimensional correlation spectroscopy (2D-CoS) verified that the sequential shift of hydroxyl group and intramolecular/intermolecular hydrogen bonds, the functional groups governing cellulose crystal structure and stability, accounted for the ultrasonication-induced transition of cellulose crystalline structure. This study provides a comprehensive picture of cellulose structure and property response caused by mechanistic treatments and will open up avenues to develop novel pretreatments for efficient utilization.

Plant cellulose synthase membrane protein isolation directly from Pichia pastoris protoplasts, liposome reconstitution, and its enzymatic characterization

Cellulose is synthesized by a plant cell membrane-integrated processive glycosyltransferase (GT) called cellulose synthase (CesA). Since only a few of these plant CesAs have been purified and characterized to date, there are huge gaps in our mechanistic understanding of these enzymes. The biochemistry and structural biology studies of CesAs are currently hampered by challenges associated with their expression and extraction at high yields. To aid in understanding CesA reaction mechanisms and to provide a more efficient CesA extraction method, two putative plant CesAs - PpCesA5 from Physcomitrella patens and PttCesA8 from Populus tremula x tremuloides that are involved in primary and secondary cell wall formation in plants were expressed using Pichia pastoris as an expression host. We developed a protoplast-based membrane protein extraction approach to directly isolate these membrane-bound enzymes, as confirmed by immunoblotting and mass spectrometry-based analyses. Our method gives 3-4-fold higher purified protein yield than the standard cell homogenization protocol. Our method resulted in liposome reconstituted CesA5 and CesA8 enzymes with similar Michaelis-Menten kinetic constants, K_m = 167 μM, 108 μM and V_max = 7.88 × 10^-5 μmol/min, 4.31 × 10^-5 μmol/min, respectively, in concurrence with the previous studies for enzymes isolated using the standard protocol. Taken together, these results suggest that CesAs involved in primary and secondary cell wall formation can be expressed and purified using a simple and more efficient extraction method. This protocol could help isolate enzymes that unravel the mechanism of native and engineered cellulose synthase complexes involved in plant cell wall biosynthesis.

Probing the evolutionary mechanism of the hydrogen bond network of cellulose nanofibrils using three DESs

Complex interactions between cellulose molecules and small molecules in Deep Eutectic Solvent (DES) systems can lead to dramatic changes in the structure of the hydrogen bond network in cellulose. However, the mechanism of interaction between cellulose and solvent molecules and the mechanism of evolution of hydrogen bond network are still unclear. In this study, cellulose nanofibrils (CNFs) were treated with DESs based on oxalic acid as hydrogen bond donors (HBD), and choline chloride, betaine, and N-methylmorpholine-N-oxide (NMMO) as hydrogen bond acceptors (HBA). The changes in the properties and microstructure of CNFs during treatment with the three types of solvents were investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results showed that the crystal structures of CNFs were not changed during the process, but the hydrogen bond network evolved, increasing the crystallinity and crystallite size. Further analysis of the fitted peaks of FTIR and generalized two-dimensional correlation spectra (2DCOS) revealed that all three hydrogen bonds were disrupted to different degrees, the relative content changed, and evolved strictly in a certain order. These findings indicate that the evolution of hydrogen bond networks in nanocellulose has certain regularity.

Cellulosic Ethanol Production from Weed Biomass Hydrolysate of Vietnamosasa pusilla

Lignocellulosic biomass can be used as a renewable and sustainable energy source to help reduce the consequences of global warming. In the new energy age, the bioconversion of lignocellulosic biomass into green and clean energy displays remarkable potential and makes efficient use of waste. Bioethanol is a biofuel that can diminish reliance on fossil fuels while minimizing carbon emissions and increasing energy efficiency. Various lignocellulosic materials and weed biomass species have been selected as potential alternative energy sources. Vietnamosasa pusilla, a weed belonging to the Poaceae family, contains more than 40% glucan. However, research on the applications of this material is limited. Thus, here we aimed to achieve maximum fermentable glucose recovery and bioethanol production from weed biomass (V. pusilla). To this end, V. pusilla feedstocks were treated with varying concentrations of H₃PO₄ and then subjected to enzymatic hydrolysis. The results indicated that after pretreatment with different concentrations of H₃PO₄, the glucose recovery and digestibility at each concentration were markedly enhanced. Moreover, 87.5% of cellulosic ethanol was obtained from V. pusilla biomass hydrolysate medium without detoxification. Overall, our findings reveal that V. pusilla biomass can be introduced into sugar-based biorefineries to produce biofuels and other valuable chemicals.

Preparation of Cellulose Nanocrystals: Controlling the Crystalline Type by One-Pot Acid Hydrolysis

Cellulose nanocrystals (CNCs) have aroused increasing interest owing to their renewable origin and excellent properties derived from their size and morphology. Based on their chain orientation, CNCs can be prepared as two main allomorphs (I or II). However, achieving pure CNC allomorphs still requires enhanced control on the CNCs synthesis process and improved understanding of the involved reaction parameters. In this work, we study in detail a set of parameters for CNC synthesis using one-pot acid hydrolysis and evaluate their influence on the outcome with respect to yield, purity, and repeatability. We also demonstrate that a fast, nondestructive, and accurate methodology based on dynamic light scattering is an efficient alternative to the usual structural analysis of the synthesis outcome. Finally, we provide an improved protocol to reliably obtain each allomorph with mass yields of 25% for type I and 40% for type II. Emphasis is put on the reduction of the environmental impact and the overall preparation time.

Degradation of cellulose polymorphs into glucose by HCl gas with simultaneous suppression of oxidative discoloration

As cellulose is the main polysaccharide in biomass, its degradation into glucose is a major undertaking in research concerning biofuels and bio-based platform chemicals. Here, we show that pressurized HCl gas is able to efficiently hydrolyze fibers of different crystalline forms (polymorphs) of cellulose when the water content of the fibers is increased to 30-50 wt%. Simultaneously, the harmful formation of strongly chromophoric humins can be suppressed by a simple addition of chlorite into the reaction system. 50-70 % glucose yields were obtained from cellulose I and II polymorphs while >90 % monosaccharide conversion was acquired from cellulose III_II after a mild post-hydrolysis step. Purification of the products is relatively unproblematic from a gas-solid mixture, and a gaseous catalyst is easier to recycle than the aqueous counterpart. The results lay down a basis for future practical solutions in cellulose hydrolysis where side reactions are controlled, conversion rates are efficient, and the recovery of products and reagents is effortless.

Study on the effects of different pectinase/cellulase ratios and pretreatment times on the preparation of nanocellulose by ultrasound-assisted bio-enzyme heat treatment

With the development of science and technology, efficient, fast and green methods are increasingly being pursued. The production of nanocellulose by green methods, such as bio-enzymes-assisted ultrasound treatment, has been the focus of many studies. However, the yield of cellulose nanocrystals prepared by this method is very low. In this paper, by pretreatment of microcrystalline cellulose (MCC), nanocellulose was prepared by heating and stirring + pectinase/cellulase + ultrasonic treatment (HSt - P/C - Ultr). The effects of the ratios of pectinase and cellulase and the hydrolysis time on the yield of nanocellulose were studied. FTIR, XRD, SEM, TEM and TG were used to determine the structure, crystallinity, morphology and thermal stability of nanocellulose. The results showed that optimal hydrolysis conditions were determined as a pectinase : cellulase ratio of 1 : 1, 90 min and 50 °C. The yield of nanocellulose was about 32.0%. The yield of pectinase cellulase = 1 : 1 was higher than that of microcrystalline cellulose (MCC) treated by a single bio-enzyme. This indicated that the synergistic effects of pectinase and cellulase have a certain effect on the formation of nanocellulose. During the preparation, the crystalline form of cellulose did not change. It was still cellulose I with a crystallinity of 73.5%, which is 9.50% higher than that of microcrystalline cellulose (MCC), a width of 20-50 nm, a high aspect ratio and a winding network structure. Therefore, nanocellulose prepared by this method is an ideal toughening material for manufacturing composite materials.

Effects of interfacial dynamics on the damping of biocomposites

A damping model is developed based on the mechanism of interfacial interaction in nanoscale particle reinforced composites. The model includes the elasticity of the materials and the effects of interfacial adhesion hysteresis. Specific results are given for the case of bio-based PA610 polyamide reinforced by nanocrystalline cellulose (CNC), based on a previous study that showed this composite possesses very high damping. The presence of hydrogen bonding at the interface between the particle and matrix and the large interfacial area due to the filler's nano size are shown to be the main causes of the high damping enhancement. The influence of other parameters, such as interfacial distance and stiffness of the matrix materials are also discussed. The modeling work can be used as a guide in designing composites with good damping properties.

Supramolecular Deconstruction of Bamboo Holocellulose via Hydrothermal Treatment for Highly Efficient Enzymatic Conversion at Low Enzyme Dosage

Hydrothermal pretreatment (HTP) has long been considered as an efficient and green treatment process on lignocellulosic biomass for bioconversion. However, the variations of cellulose supramolecular structures during HTP as well as their effects on subsequent enzymatic conversion are less understood. In this work, bamboo holocellulose with well-connected cellulose and hemicelluloses polysaccharides were hydrothermally treated under various temperatures. Chemical, morphological, and crystal structural determinations were performed systematically by a series of advanced characterizations. Xylan was degraded to xylooligosaccharides in the hydrolyzates accompanied by the reduced degree of polymerization for cellulose. Cellulose crystallites were found to swell anisotropically, despite the limited decrystallization by HTP. Hydrogen bond linkages between cellulose molecular chains were weakened due to above chemical and crystal variations, which therefore swelled, loosened, and separated the condensed cellulose microfibrils. Samples after HTP present notably increased surface area, favoring the adsorption and subsequent hydrolysis by cellulase enzymes. A satisfying enzymatic conversion yield (>85%) at rather low cellulase enzyme dosage (10 FPU/g glucan) was obtained, which would indicate new understandings on the green and efficient bioconversion process on lignocellulosic biomass.

Single-molecule investigations of single-chain cellulose biosynthesis

Cellulose biosynthesis in sessile bacterial colonies originates in the membrane-integrated bacterial cellulose synthase (Bcs) AB complex. We utilize optical tweezers to measure single-strand cellulose biosynthesis by BcsAB from Rhodobacter sphaeroides. Synthesis depends on uridine diphosphate glucose, Mg²⁺, and cyclic diguanosine monophosphate, with the last displaying a retention time of ∼80 min. Below a stall force of 12.7 pN, biosynthesis is relatively insensitive to force and proceeds at a rate of one glucose addition every 2.5 s at room temperature, increasing to two additions per second at 37°. At low forces, conformational hopping is observed. Single-strand cellulose stretching unveiled a persistence length of 6.2 nm, an axial stiffness of 40.7 pN, and an ability for complexes to maintain a tight grip, with forces nearing 100 pN. Stretching experiments exhibited hysteresis, suggesting that cellulose microstructure underpinning robust biofilms begins to form during synthesis. Cellohexaose spontaneously binds to nascent single cellulose strands, impacting polymer mechanical properties and increasing BcsAB activity.

Investigation into Lewis and Brønsted acid interactions between metal chloride and aqueous choline chloride-oxalic acid for enhanced furfural production from lignocellulosic biomass

Furfural has been identified as a valuable biobased platform chemical that can be further converted into bioenergy and biochemicals. Furfural is derived from lignocellulosic biomass and can also be regarded as a sustainable alternative to petrochemical products. Herein, the performance of trivalent metal chlorides (FeCl₃, AlCl₃) and tetravalent metal chlorides (SnCl₄, TeCl₄) as Lewis acidic cocatalysts was investigated in an aqueous choline chloride-oxalic acid (16.4 wt% H₂O) deep eutectic solvent (DES) system for producing furfural from oil palm fronds (OPFs). The metal chlorides with greater electrical field gradients were stronger Lewis acids that enhanced both furfural production and degradation reactions. The main degradation product in this reaction system was humin, and this result was confirmed by FTIR analysis. By subjecting OPFs to an aqueous DES reaction (120 °C, 45 min) with SnCl₄ (2.50 wt%), a furfural yield of 59.4% was obtained; without incorporated metal chlorides, the furfural yield was 46.1%. Characterization studies showed synergistic Lewis and Brønsted acid interactions between metal chlorides and DES components. Overall, the residual OPFs showed high glucan content, which led to the production of glucose (71.4%) as a byproduct via enzymatic hydrolysis. Additionally, the aqueous DES system was recycled and reused for several additional runs. The proposed aqueous DES system presents a promising biorefinery approach for the conversion of OPFs to biochemicals.

Cellulolytic and Xylanolytic Enzymes from Yeasts: Properties and Industrial Applications

Lignocellulose, the main component of plant cell walls, comprises polyaromatic lignin and fermentable materials, cellulose and hemicellulose. It is a plentiful and renewable feedstock for chemicals and energy. It can serve as a raw material for the production of various value-added products, including cellulase and xylanase. Cellulase is essentially required in lignocellulose-based biorefineries and is applied in many commercial processes. Likewise, xylanases are industrially important enzymes applied in papermaking and in the manufacture of prebiotics and pharmaceuticals. Owing to the widespread application of these enzymes, many prokaryotes and eukaryotes have been exploited to produce cellulase and xylanases in good yields, yet yeasts have rarely been explored for their plant-cell-wall-degrading activities. This review is focused on summarizing reports about cellulolytic and xylanolytic yeasts, their properties, and their biotechnological applications.

Thermophilic Geobacillus WSUCF1 Secretome for Saccharification of Ammonia Fiber Expansion and Extractive Ammonia Pretreated Corn Stover

A thermophilic Geobacillus bacterial strain, WSUCF1 contains different carbohydrate-active enzymes (CAZymes) capable of hydrolyzing hemicellulose in lignocellulosic biomass. We used proteomic, genomic, and bioinformatic tools, and genomic data to analyze the relative abundance of cellulolytic, hemicellulolytic, and lignin modifying enzymes present in the secretomes. Results showed that CAZyme profiles of secretomes varied based on the substrate type and complexity, composition, and pretreatment conditions. The enzyme activity of secretomes also changed depending on the substrate used. The secretomes were used in combination with commercial and purified enzymes to carry out saccharification of ammonia fiber expansion (AFEX)-pretreated corn stover and extractive ammonia (EA)-pretreated corn stover. When WSUCF1 bacterial secretome produced at different conditions was combined with a small percentage of commercial enzymes, we observed efficient saccharification of EA-CS, and the results were comparable to using a commercial enzyme cocktail (87% glucan and 70% xylan conversion). It also opens the possibility of producing CAZymes in a biorefinery using inexpensive substrates, such as AFEX-pretreated corn stover and Avicel, and eliminates expensive enzyme processing steps that are used in enzyme manufacturing. Implementing in-house enzyme production is expected to significantly reduce the cost of enzymes and biofuel processing cost.

Comparative study on the hydrogenolysis performance of solid residues from different bamboo pretreatments

Both alkaline organosolv and formaldehyde stabilization pretreatment can yield high-quality lignin by preventing condensation. For the hydrogenolysis of the pretreated solid residues, the highest yield of C2-C4 chemicals was 66.8% under alkaline organosolv pretreatment for 60 min. Specifically, the crimped fibers and residual lignin and hemicellulose increased the surface roughness of the residue by 40.6%, the crystallinity index decreased to 44.4%, and the crystal size was reduced to 2.15 nm, which in turn promoted hydrogenolysis of the residue. However, the increase of crystallinity and crystal size and the decrease in surface roughness of the formaldehyde stabilization pretreatment residue greatly hindered the conversion of polysaccharides. In addition, residual formaldehyde on the residue may also inhibit catalyst activity. Overall, this study provides novel perspectives on the full utilization of biomass, as well as new insights into the conversion of polysaccharides.

Hemp and Its Derivatives as a Universal Industrial Raw Material (with Particular Emphasis on the Polymer Industry)-A Review

This review article provides basic information about cannabis, its structure, and its impact on human development at the turn of the century. It also contains a brief description of the cultivation and application of these plants in the basic branches of the economy. This overview is also a comprehensive collection of information on the chemical composition of individual cannabis derivatives. It contains the characteristics of the chemical composition as well as the physicochemical and mechanical properties of hemp fibers, oil, extracts and wax, which is unique compared to other review articles. As one of the few articles, it approaches the topic in a holistic and evolutionary way, moving through the plant’s life cycle. Its important element is examples of the use of hemp derivatives in polymer composites based on thermoplastics, elastomers and duroplasts and the influence of these additives on their properties, which cannot be found in other review articles on this subject. It indicates possible directions for further technological development, with particular emphasis on the pro-ecological aspects of these plants. It indicates the gaps and possible research directions in basic knowledge on the use of hemp in elastomers.

Co-production of xylooligosaccharides and glucose from birch sawdust by hot water pretreatment and enzymatic hydrolysis

A green method for co-production of value-added xylooligosaccharides (XOS) and glucose from birch was demonstrated using hot water pretreatment. Effects of pretreatment severity factor (Log R₀) on XOS production and enzymatic hydrolysis were investigated. At Log R₀ of 4.05 (180 °C, 50 min), the maximum hydrolysis yield (80.8%) was obtained. At Log R₀ of 3.91 (170 °C, 70 min), the maximum XOS yield (46.1%) was obtained, however the hydrolysis yield decreased to 70.3%. To achieve both the high XOS yield and high glucose output, Tween 80 addition (0.075 g/g cellulose) was employed, leading to an improvement in hydrolysis yield from 70.3% to 89.4%. From a mass balance perspective, 104.6 g of XOS and 372.9 g of glucose could be produced from 1000 g birch. These results demonstrated that birch sawdust is a promising lignocellulosic material for co-production of XOS and glucose.

A comprehensive investigation on cellulose nanocrystals with different crystal structures from cotton via an efficient route

The crystal structures of cellulose nanomaterials play an important role in their morphologies and applications, however, there was still lacking systematic research on preparing various crystalline allomorphs of cellulose nanocrystals with high thermal stability. Herein, the efficient synthesis route was presented to design various crystalline allomorphs of cellulose from cotton. And then, cellulose nanocrystals with different crystal structures (CNC-I, CNC-II, CNC-III_II, CNC-IV_II) were prepared by hydrogen peroxide hydrolysis of resultant cellulose. Overall, needle-like CNC-I (length of 180 ± 25 nm, diameter of 12 ± 2 nm), near-spherical CNC-II (diameter of 101 ± 12 nm), and spherical CNC-III_II (diameter of 22 ± 3 nm) and CNC-IV_II (diameter of 21 ± 2 nm) all exhibited remarkable dispersibility and thermal stability (T_max > 357 °C). This work provides a simple and low-cost synthesis route for various crystalline allomorphs of CNCs with high thermal stability from the same raw materials (cotton).

Combined oxidization and liquid ammonia pretreatment of bamboo of various ages and species for maximizing fermentable sugar release

To determine the potential for improving biomass enzymolysis, a combined oxidization and liquid ammonia pretreatment (OD-LAT) was employed for bamboo. The effects of oxidant, bamboo ages, and species on the pretreatment effectiveness and subsequent enzymolysis were studied. Under the optimal OD-LAT pretreatment and enzymolysis of the B-NA bamboo Neosinocalamus affinis, the glucan and xylan conversion reached 83.85% and 78.66%, respectively, and approximately 59.7-68.5 g of fermentable sugars can be produced per 100 g of dry bamboo, which was an approximately 5-8 fold increase compared with untreated sample. The H₂O₂ loading of 1.0 was the optimal oxidant dosage for the OD-LAT process. The OD-LAT pretreatment was only suitable for bamboo under three-year-old, and it significantly improved the enzymolysis of B-NA and B-BM, while it was limited to B-DO and B-PP. The pretreatment effects of bamboo were not only related to composition but also to the bamboo age, species, macro-structures and micro-structures.

Processive Enzymes Kept on a Leash: How Cellulase Activity in Multienzyme Complexes Directs Nanoscale Deconstruction of Cellulose

Biological deconstruction of polymer materials gains efficiency from the spatiotemporally coordinated action of enzymes with synergetic function in polymer chain depolymerization. To perpetuate enzyme synergy on a solid substrate undergoing deconstruction, the overall attack must alternate between focusing the individual enzymes locally and dissipating them again to other surface sites. Natural cellulases working as multienzyme complexes assembled on a scaffold protein (the cellulosome) maximize the effect of local concentration yet restrain the dispersion of individual enzymes. Here, with evidence from real-time atomic force microscopy to track nanoscale deconstruction of single cellulose fibers, we show that the cellulosome forces the fiber degradation into the transversal direction, to produce smaller fragments from multiple local attacks ("cuts"). Noncomplexed enzymes, as in fungal cellulases or obtained by dissociating the cellulosome, release the confining force so that fiber degradation proceeds laterally, observed as directed ablation of surface fibrils and leading to whole fiber "thinning". Processive cellulases that are enabled to freely disperse evoke the lateral degradation and determine its efficiency. Our results suggest that among natural cellulases, the dispersed enzymes are more generally and globally effective in depolymerization, while the cellulosome represents a specialized, fiber-fragmenting machinery.

Current perspective on production and applications of microbial cellulases: a review

The potential of cellulolytic enzymes has been widely studied and explored for bioconversion processes and plays a key role in various industrial applications. Cellulase, a key enzyme for cellulose-rich waste feedstock-based biorefinery, has increasing demand in various industries, e.g., paper and pulp, juice clarification, etc. Also, there has been constant progress in developing new strategies to enhance its production, such as the application of waste feedstock as the substrate for the production of individual or enzyme cocktails, process parameters control, and genetic manipulations for enzyme production with enhanced yield, efficiency, and specificity. Further, an insight into immobilization techniques has also been presented for improved reusability of cellulase, a critical factor that controls the cost of the enzyme at an industrial scale. In addition, the review also gives an insight into the status of the significant application of cellulase in the industrial sector, with its techno-economic analysis for future applications. The present review gives a complete overview of current perspectives on the production of microbial cellulases as a promising tool to develop a sustainable and greener concept for industrial applications.

Promoting enzymatic hydrolysis of aggregated bamboo crystalline cellulose by fast microwave-assisted dicarboxylic acid deep eutectic solvents pretreatments

Deep eutectic solvents (DESs) have received considerable interests as pretreatment solvents for biorefinery. In the present work, five kinds of dicarboxylic acids based DESs were introduced to pretreatments on moso bamboo (MB) with microwave irradiation assistance. Factors influencing the enzymatic conversion of MB cellulose to glucose were determined. With the fast heating, pretreated samples all present significant delignification and hemicelluloses matrix removal, thus improving the enzymatic conversion yield from 15% of MB to ~60%. For the DESs, hydrogen donors with less carbon atoms (oxalic acid) and more hydroxyl groups (tartaric acid) displayed higher efficiency due to separation of aggregated cellulose microfibrils. The microwave assisted DESs (MW-DESs) pretreatments also contributed to cellulose crystal variations including decrystallization and more exposure of hydrophobic surfaces, which are beneficial for followed cellulase adsorption and hydrolysis. The exploration of fast MW-DESs pretreatments may expand the potentials of lignocellulose biomass on effective and applicable biorefinery.

Accelerating Selective Oxidation of Biomass-Based Hydroxyl Compounds with Hydrogen Bond Acceptors

Hydrogen-bonding-initiated self-association makes the valorization of biomass-based hydroxyl compounds a formidable challenge at high concentration. Apart from enhancing the dehydration reaction of hydroxyl compounds with the noncovalent medium effects, insights into how these effects can be exploited to optimize the oxidative reactivity of concentrated hydroxyl compounds remain unclear. Herein, we elucidate that deaggregation of hydroxyl groups with a catalytic number of hydrogen bond acceptors is essential in improving the reactivity of the aerobic oxidation of biomass-based neat aromatic alcohols over the vanadium-based catalyst. The neat 5-hydroxymethylfurfural (HMF) deaggregated with 25 mol % N,N-dimethylformamide (DMF) shows a >7-fold increase in reactivity to produce corresponding aldehydes with excellent selectivity, in stark contrast to the contrary deactivation of reaction in excessive DMF.

Factors Affecting the Catalytic Efficiency and Synergism of Xylanase and Cellulase During Enzymatic Hydrolysis of Birch Wood

Understanding factors that affect the catalytic efficiency and synergism of enzymes is helpful to enhance the process of bioconversion. In this study, birch wood (BW) was sequentially treated by delignification (DL), deacetylation (DA), and decrystallization (DC) treatments. The physiochemical structures of treated BW were characterized. Moreover, the influences of sequential treatments on the catalytic efficiency and synergism of xylanase and cellulase were studied. DL treatments efficiently improved the conversion of cellulose and xylan. A high degree of synergy (DS) between xylanase and cellulase was produced during hydrolysis of DL-treated BW. DA treatments enhanced xylan conversion but reduced the DS between xylanase and cellulase for xylan hydrolysis, whereas DC treatments enhanced cellulose conversion but reduced the DS between xylanase and cellulase for cellulose hydrolysis. The cellulose conversion of lithium chloride/N,N-dimethylacetamide (LiCl/DMAc)-treated BW (89.69%) was higher than the cellulose conversion of ball milling (BM)-treated BW (81.63%), whereas the xylan conversion of LiCl/DMAc-treated BW (83.77%) was lower than the xylan conversion of BM-treated BW (87.21%). This study showed that the catalytic efficiency and synergism of xylanase and cellulase are markedly affected by lignin hindrance, hemicellulose acetylation, and cellulose crystallization.

Effect of amorphous cellulose on the deformation behavior of cellulose composites: molecular dynamics simulation

This study was aimed at predicting and enhancing the properties of the blend, as well as exploring the mechanism, of a polylactic acid (PLA)/amorphous cellulose composite system through molecular characterization. The static properties of the amorphous cellulose/PLA blend model and the mechanical response of the material under uniaxial tension were studied by molecular dynamics simulation to establish the structure-property relationship. PLA and cellulose showed poor miscibility, the change in the compatibility of the mixture can be attributed to the hydrogen bond interaction between the cellulose and PLA functional groups. The radius of gyration, interaction and free volume of the molecular chain in the blend were analyzed. The conformational changes under tensile deformation indicated that the load-bearing role of cellulose in the system was the main reason for increasing the strength of the material. The yield process was considered to be the infiltration of free volume caused by deformation.

Increased mixing intensity is not necessary for more efficient cellulose hydrolysis at high solid loading

To enhance the cellulose hydrolysis at high solid loadings, an increased mixing intensity is generally required for the high solid loading hydrolysis, while it leads to higher energy consumption. In this study, the impact of mixing intensity on cellulose conversion during hydrolysis at different solid loadings were systematically studied. It was found that the increased mixing intensity is not necessary for more efficient cellulose hydrolysis. For cellulose hydrolysis at higher solid loadings, a lower mixing intensity is needed for a higher cellulose conversion. Although the increased mixing intensity promoted enzyme adsorption, it strengthened product inhibition and caused severer enzyme deactivation. Besides, mixing at the initial stage of cellulose hydrolysis was more crucial, while continuous mixing throughout the hydrolysis was not required for more efficient cellulose hydrolysis. Based on the mechanism study, a combined mixing strategy was developed to achieve efficient cellulose hydrolysis with about two-third reduction in energy consumption.

Features correlated to improved enzymatic digestibility of corn stover subjected to alkaline hydrogen peroxide pretreatment

As one of the leading pretreatment approaches, alkaline hydrogen peroxide (AHP) pretreatment can enhance the enzymatic digestibility of lignocellulose significantly. In this study, the glucan conversion of AHP pretreated corn stover (CS) without and with water-wash were 28.4% and 50.0% higher than that of raw material, respectively. In order to systematically understand its mechanism, analyses of the features of AHP pretreated and raw CS, such as specific surface area, crystallinity, zeta potential, water holding capacity and swelling capacity and others were performed. The weight-average molecular weight (Mw) of the sugars in the hydrolysate and the particle size distribution of the hydrolysis residue were also analyzed. These results explained why AHP-CS was more conducive to enzymatic hydrolysis. The deeper reason was that the removal of lignin and the destruction of hydrogen bonds within cellulose and hemicellulose increased the accessibility of cellulose and reduced the non-productive adsorption of cellulase, which significantly improved the enzymatic digestibility.

Molecular origins of reduced activity and binding commitment of processive cellulases and associated carbohydrate-binding proteins to cellulose III

Efficient enzymatic saccharification of cellulosic biomass into fermentable sugars can enable production of bioproducts like ethanol. Native crystalline cellulose, or cellulose I, is inefficiently processed via enzymatic hydrolysis but can be converted into the structurally distinct cellulose III allomorph that is processed via cellulase cocktails derived from Trichoderma reesei up to 20-fold faster. However, characterization of individual cellulases from T. reesei, like the processive exocellulase Cel7A, shows reduced binding and activity at low enzyme loadings toward cellulose III. To clarify this discrepancy, we monitored the single-molecule initial binding commitment and subsequent processive motility of Cel7A enzymes and associated carbohydrate-binding modules (CBMs) on cellulose using optical tweezers force spectroscopy. We confirmed a 48% lower initial binding commitment and 32% slower processive motility of Cel7A on cellulose III, which we hypothesized derives from reduced binding affinity of the Cel7A binding domain CBM1. Classical CBM–cellulose pull-down assays, depending on the adsorption model fitted, predicted between 1.2- and 7-fold reduction in CBM1 binding affinity for cellulose III. Force spectroscopy measurements of CBM1–cellulose interactions, along with molecular dynamics simulations, indicated that previous interpretations of classical binding assay results using multisite adsorption models may have complicated analysis, and instead suggest simpler single-site models should be used. These findings were corroborated by binding analysis of other type-A CBMs (CBM2a, CBM3a, CBM5, CBM10, and CBM64) on both cellulose allomorphs. Finally, we discuss how complementary analytical tools are critical to gain insight into the complex mechanisms of insoluble polysaccharides hydrolysis by cellulolytic enzymes and associated carbohydrate-binding proteins.

Structural and Morphological Analysis of Cellulose Pulp Produced from the Fractionation of Eucalyptus obliqua Sawdust Using γ-Valerolactone

Organic solvents offer promising methods for the fractionation of Eucalyptus obliqua lignocellulosic biomass. This study investigated the impact of γ-valerolactone (GVL) fractionation on the morphology of cellulose and its internal structure using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. The solubilized lignin precipitated on the macrofibril surface as lignin spheres. GVL fractionation significantly increased the crystallinity of the recovered pulps from 0.29 for the sawdust to an average of 0.53 and a maximum of 0.66. The main states of cellulose that were susceptible to hydrolysis during the fractionation were amorphous and surface cellulose, both of which were reduced significantly, while paracrystalline and pure crystalline fractions in the pulp increased. It was concluded that GVL fractionation can produce a crystalline cellulose pulp of high quality suitable for further processing.

Generation of highly amenable cellulose-Iβ via selective delignification of rice straw using a reusable cyclic ether-assisted deep eutectic solvent system

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. The enzymatic hydrolysis of cellulose is necessary for generating monomeric sugars, which are then fermented into ethanol. In our study, a combination of a deep eutectic (DE) mixture (of 2-aminoethanol and tetra-n-butyl ammonium bromide) and a cyclic ether (tetrahydrofuran) was used for selective delignification of rice straw (RS) under mild conditions (100 °C). Pretreatment with DE-THF solvent system caused ~ 46% delignification whereas cellulose (~ 91%) and hemicellulose (~ 67%) recoveries remained higher. The new solvent system could be reused upto 10 subsequent cycles with the same effectivity. Interestingly, the DE-THF pretreated cellulose showed remarkable enzymatic hydrolysability, despite an increase in its crystallinity to 72.3%. Contrary to conventional pretreatments, we report for the first time that the enzymatic hydrolysis of pretreated cellulose is enhanced by the removal of lignin during DE-THF pretreatment, notwithstanding an increase in its crystallinity. The current study paves way for the development of newer strategies for biomass depolymerization with DES based solvents.

Crystalline stability of cellulose III nanocrystals in the hydrothermal treatment and NaOH solution

To better understand the system and conversion of cellulose allomorphs, cellulose III nanocrystals (CNC-III) were used to investigate the crystalline stability of cellulose III in the hydrothermal condition and a lower concentrated NaOH-water system. It was shown that H₂O or alkali played an important role in the process of polymorphic transformation. The CNC-III allomorph turned back to cellulose I with an extremely low crystallinity (∼4.18 %) during hydrothermal process at 90-95 °C, or cellulose II when the temperature excessed boiling point (≥100 °C). Furthermore, CNC-III could be rapidly dissolved in an aqueous NaOH (∼7 wt.%) without a pre-cooled treatment to obtain its stable solution. Afterwards, cellulose II with a steady average crystallite size (∼34) was acquired after the regeneration process via dialysis with distilled water. The polymorphic transformation was also analyzed by X-ray diffraction (XRD), solid-state ¹³C nuclear magnetic resonance (¹³C NMR).

Fabrication and characterization of cellulose nanoparticles from maize stalk pith via ultrasonic-mediated cationic etherification

In this study, parenchyma cellulose, which was extracted from maize stalk pith as an abundant source of agricultural residues, was applied for preparing cellulose nanoparticles (CNPs) via an ultrasound-assisted etherification and a subsequent sonication process. The ultrasonic-assisted treatment greatly improved the modification of the pith cellulose with glycidyltrimethylammonium chloride, leading to a partial increase in the dissolubility of the as-obtained product and thus disintegration of sheet-like cellulose into nanoparticles. While the formation of CNPs by ultrasonication was largely dependent on the cellulose consistency in the cationic-modified system. Under the condition of 25% cellulose consistency, the longer sono-treated duration yielded a more stable and dispersible suspension of CNP due to its higher zeta potential. Degree of substitution and FT-IR analyses indicated that quaternary ammonium salts were grafted onto hydroxyl groups of cellulose chain. SEM and TEM images exhibited the CNP to have spherical morphology with an average dimeter from 15 to 55 nm. XRD investigation revealed that CNPs consisted mainly of a crystalline cellulose Ι structure, and they had a lower crystallinity than the starting cellulose. Moreover, thermogravimetric results illustrated the thermal resistance of the CNPs was lower than the pith cellulose. The optimal CNP with highly cationic charges, good stability and acceptable thermostability might be considered as one of the alternatively renewable reinforcement additives for nanocomposite production.

Carbohydrate-binding module O-mannosylation alters binding selectivity to cellulose and lignin

Improved understanding of the effect of protein glycosylation is expected to provide the foundation for the design of protein glycoengineering strategies. In this study, we examine the impact of O-glycosylation on the binding selectivity of a model Family 1 carbohydrate-binding module (CBM), which has been shown to be one of the primary sub-domains responsible for non-productive lignin binding in multi-modular cellulases. Specifically, we examine the relationship between glycan structure and the binding specificity of the CBM to cellulose and lignin substrates. We find that the glycosylation pattern of the CBM exhibits a strong influence on the binding affinity and the selectivity between both cellulose and lignin. In addition, the large set of binding data collected allows us to examine the relationship between binding affinity and the correlation in motion between pairs of glycosylation sites. Our results suggest that glycoforms displaying highly correlated motion in their glycosylation sites tend to bind cellulose with high affinity and lignin with low affinity. Taken together, this work helps lay the groundwork for future exploitation of glycoengineering as a tool to improve the performance of industrial enzymes.

Improved understanding of the effect of protein glycosylation is expected to provide the foundation for the design of protein glycoengineering strategies.

Combinations of alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide pretreatments of corn stalk for improved biomethanation

The purpose of this study was to improve methane generation from corn stalk (CS) through alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide (AHP-LiCl/DMAc) pretreatment. Changes in the structures of treated and untreated CSs were investigated, and biomass components, including cellulose, hemicellulose and lignin, were analysed. Our findings revealed that AHP-LiCl/DMAc pretreatment improved accumulative methane yield by forceful delignification and effectively destroyed the structure of cellulose. The AHP-LiCl/DMAc-treated group had a maximum methane yield of 318.6 ± 17.85 mL/g volatile solid, which was 40.08% and 10.10% higher than the maximum methane yields of the untreated and AHP-treated group, respectively. This result showed enhanced cellulose dissolution by the ionic solvent of LiCl/DMAc and improved enzymatic saccharification in fermentative bacteria without structural modifications. The AHP-LiCl/DMAc treated group had higher glucose level, acetate followed by biomethanation process. Furthermore, the decrease in crystallinity indexes for AHP-LiCl/DMAc treated group was reported. Overall, this investigation proved a promising pretreatment approach for enhancing the degradation of CS into reducing sugars and improving methane generation.

Temperature-Dependent Blue Shifting of O-H Stretching Frequencies in Crystalline Cellulose Explained

Increasing the temperature of a chemical system generally causes covalent bonds to lengthen and weaken, often the first step in initiating chemical reactions. However, for some hydrogen-bonded systems, infrared (IR) spectroscopy measurements reveal that covalent O-H bonds actually strengthen and therefore shorten when heated. In 1957, Finch and Lippincott proposed a simple one-dimensional (1D) model to explain this effect, in which thermal excitation of intermolecular stretching modes leads to lengthening and weakening of intermolecular O-H···O hydrogen bonds, thereby indirectly strengthening the associated covalent O-H bonds. Taking cellulose (an infinitely repeating polymer of d-glucose) as an example, we use molecular dynamics modeling to show that the same mechanism is responsible for temperature-dependent blue shifting of O-H stretching bands in IR spectra of carbohydrate biopolymers, except that interchain hydrogen bonds are weakened by thermal excitation of chain-separation modes, while intrachain hydrogen bonds are weakened by thermally induced changes in ring puckering and orientation of ring substituents but not reorientation of glucose units relative to one another or overall twisting of the cellulose chains.

Deconstruction of oriented crystalline cellulose by novel levulinic acid based deep eutectic solvents pretreatment for improved enzymatic accessibility

Discovering green solvents and their inner mechanisms for efficient deconstruction of lignocellulosic biomass recalcitrance are receiving growing interests. In this work, eco-friendly levulinic acid (LA) based deep eutectic solvents (DES) were proposed for pretreatment on moso bamboo by combining acetamide (Am), betaine (Ba) and choline chloride (ChCl) as hydrogen bonding acceptors. LA/ChCl pretreated materials showed optimal enzymatic accessibility with the highest glucose yield (79.07%) because of its higher lignin removal, morphological disruption and decreased crystallinity. Moreover, the microvoids (averagely 30 nm) and cracks were observed for cellulose microfibrils in anisotropic directions, which resulted in shorter microfibrils and crystallites facilitating the enzymatic hydrolysis. The studies on recyclability revealed that LA/Ba DES had better recycling performance due to its maintaining capability of lignin extraction. Series of supramolecular changes on oriented crystalline cellulose were determined in this work by novel LA based DES, which may provide new alternatives for biomass pretreatments.

Rapid Depolymerization of Decrystallized Cellulose to Soluble Products via Ethanolysis under Mild Conditions

Efficient cellulose depolymerization is a major bottleneck for economical production of second-generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl-glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether. In comparison, ethanolysis of the original cellulose resulted in only 3±1 % conversion. Additional soluble products from cellulose ethanolysis included carbohydrate isomers and oligomers, differing from the products obtained from hydrolysis. X-ray diffraction and nuclear magnetic resonance spectroscopy revealed increased crystallinity post-reaction, retarding further depolymerization. Hot liquid water extracted soluble oligomers from the ethanolyzed cellulose, suggesting formation of a nanoscale barrier of crystalline cellulose that traps soluble products during ethanolysis. Use of cellulose-swelling co-solvents and repeated mechanical decrystallization both proved effective at increasing cellulose conversion and soluble product yields. Repeated ball milling and ethanolysis resulted in 62±1 % cellulose conversion. Ethanolysis of decrystallized cellulose has potential for rapid (<2 h) de-polymerization at mild conditions.