Cellulose Chains Research Articles

Bacterial cellulose-based submicrobundle framework-induced hyperporous cellulose microspheres functionalized by ionic liquids for anion exchange chromatography

Ovalbumin (OVA) is widely used in food and pharmaceutical industries and can be separated using ion exchange chromatography. However, both rapid adsorption kinetics and great adsorption capacity are impeded by the nanoscale porous structures of chromatography media. Here, hyperporous cellulose microspheres (BCMs) with well-controllable micron-sized macropores are fabricated by a facile one-step pre-crosslinking strategy. Bacterial cellulose nanofibers and dissolved cellulose chains are pre-crosslinked by epichlorohydrin to form submicrobundles and generate an interconnected gel network. The preliminary gelation blocks induce a hyperporous framework during the recrystallization and assembly of regenerated cellulose. BCMs have demonstrated decreased mass transfer resistance and increased accessible active sites due to the micron-sized convective macropores (2.04 μm) and high specific surface area (194.25 m2 g−1). Cationic imidazolium ILs (AMIBr) functionalized BCMs (IL-BCMs) are prepared as anion exchangers. IL-BCMs exhibit rapid adsorption kinetics for OVA, reaching 85% of the equilibrium adsorption amount within 30 min. Additionally, IL-BCMs demonstrate endothermic chemosorption, high adsorption capacity (150.30 mg g−1, 25 °C), reusability (>85% removal efficiency after seven cycles), and selectivity towards OVA at pH 6.0. Continuous fixed-bed adsorption further suggests the practicality of IL-BCMs in ion exchange chromatography, indicating that IL-BCMs are appealing media for protein separation and purification.

Carboxylation of sulfated cellulose nanocrystals by family AA9 lytic polysaccharide monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) from the auxiliary activity 9 (AA9) family act on cellulose through an oxidative mechanism that improves cellulose saccharification in concert with other cellulolytic enzymes. Degradation and solubilization of cellulose chains are known to take place when various cellulose hierarchies, fibers, nanofibers, and cellulose nanocrystals (CNCs) are subjected to LPMOs, either alone or in combination with other cellulose acting enzymes. The use of LPMOs to modify and prepare CNCs has been proposed mostly in top-down synthesis from larger hierarchies. Here, we attempted a direct surface modification of CNCs with LPMOs with the aim of investigating the role played by the charged sulfate groups on CNCs. Sulfate half-ester groups are introduced during the preparation of CNCs from cellulose using sulfuric acid. It has been proposed that the charged sulfate groups hinder the binding of enzymes or affinity of charged reactants on the surface and hence reduce enzymatic and chemical reaction efficiency. We demonstrate the modification of commercial sulfated CNCs using a family AA9 LPMO. Conductometric titration and spectrometric characterization of the oxidized particles indicate that carboxylation of up to 10% was possible without degradation of the crystals. Unexpectedly, the carboxyl groups could only be introduced to the crystals containing sulfate groups, while desulfated crystals remained unfunctionalized. This was deemed to be due to that the sulfate groups limit the adsorption of the enzymes and hence modulate the cuts facilitated by the enzymes on the surface. This limits the release of chains from the surface and enables the carboxylation of the insoluble substrate rather than the release of the solubilized chains. This study highlights the importance of analyzing both the solid and soluble reaction products to gain insights into the oxidation mechanism. We demonstrated that 10% functionalization suffices for the use of CNCs in coupling chemistry.

Unraveling the thermodynamics of the CO2 driven precipitation of cellulose in aqueous NaOH

Hypothesis:The incorporation of carbon dioxide into a sodium hydroxide solution containing cellulose may induce the formation of a transient cellulose carbonate intermediate, which readily hydrolyzes to carbonate ion, and this process is responsible for the instantaneous formation of loose cellulose aggregates. Simulations:We employed molecular dynamics simulations to gain insight into the role of carbon dioxide and related ions in the cellulose aggregation process. By performing free energy calculations using OPLS/AA force fields between cellulose chains at different ionic environments, we were able to gain additional information regarding the behavior and thermodynamics of the involved species and propose a potential mechanism for the aggregation of cellulose in these systems. Findings:Our hypothesis of the formation of an intermediate cellulose carbonate in the solution, which strongly favors carbon dioxide absorption and carbonate ion formation, is supported by the simulation results. These results suggest that the aggregation process is driven by entropy upon the introduction of carbonate ions into the system.

Compressible, anti-freezing, and ionic conductive cellulose/polyacrylic acid composite hydrogel prepared via AlCl3/ZnCl2 aqueous system as solvent and catalyst

From the perspective of environmental sustainability, introducing cellulose into ionic conductive hydrogel is an inevitable trend for the development of flexible conductive materials. We report a double-network cellulose/polyacrylic acid (Cel/PAA) composite hydrogel based on the dissolving of cellulose by AlCl3/ZnCl2 aqueous system. The Cel/PAA composite hydrogel consists of rigid cellulose chains and flexible polyacrylic acid, which synergistically realize the improvement of the mechanical properties. The AlCl3/ZnCl2 aqueous system not only serves as the green solvent for cellulose, but also the Al3+ and Zn2+ metal ions can be served as a catalyst to activate the initiator for polymerization of acrylic acid. Compared with pure cellulose hydrogel, the compression strain of the Cel/PAA composite hydrogel was significantly improved to 80 %, and its conductivity increased by 28.1 %. In addition, its compression stress was enhanced over 2 times than pure PAA hydrogel. The Cel/PAA composite hydrogel exhibits excellent anti-freezing (−45 °C), weight retention (90 %), and conductivity (2.70 S/m) properties, still maintaining transparency and storage stability in the extreme environment. This work presents a facile strategy to develop an ionic conductive cellulose-based composite hydrogel with good conductivity and mechanical properties, which shows potential for the application fields of flexible sensors and 3D-printing functional materials.

The Viscoelastic and Hygroscopicity Behavior of Delignified and Densified Poplar Wood

The combination of alkaline delignification and densification was applied to improve wood mechanical strength. Poplar wood samples were subjected to alkali delignification with varying degrees of lignin and hemicellulose removal followed by hot pressing. Dynamic mechanical performances and dynamic sorption behavior of the untreated and densified wood were then evaluated. Results showed that appropriate removal of lignin can improve the stiffness of densified wood and reduce moisture sorption and the numbers of sorption sites. Fourier transform infrared (FTIR) microscopy along with X-ray diffraction (XRD) were used to explain the viscoelastic and hygroscopicity of delignified and densified wood. Hemicelluloses and lignin were selectively dissolved during alkali treatment. Wood crystallinity was increased after alkali treatment at a moderate concentration of 2%, beneficial to improving the dimensional stability and mechanical performance of delignified and densified wood. The crosslinking of cellulose chains through hydrogen bonding, the decreased content of free hydroxyl groups, and the increased crystallinity in the cell wall contributed to higher storage modulus and lower hydrophilicity. The results support mild delignification and densification as a feasible way towards extending the service life of wood products used as structural materials.

Visualizing Chiral Interactions in Carbohydrates Adsorbed on Au(111) by High-Resolution STM Imaging.

Carbohydrates are the most abundant organic material on Earth and the structural "material of choice" in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom-up engineering of carbohydrate materials demands an atomic-level understanding of their molecular structures and interactions in condensed phases. Here, high-resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three-dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D- and L-oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases.

Visualizing Chiral Interactions in Carbohydrates Adsorbed on Au(111) by High‐Resolution STM Imaging

AbstractCarbohydrates are the most abundant organic material on Earth and the structural “material of choice” in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom‐up engineering of carbohydrate materials demands an atomic‐level understanding of their molecular structures and interactions in condensed phases. Here, high‐resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three‐dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D‐ and L‐oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases.

Effect of amino-modified SiO2 nanoparticles on micro-water diffusion behaviour in soybean oil-based natural ester oil-paper insulation system

Nanoparticles can significantly improve the insulation property of oil-paper insulation systems. In this paper, amino-modified SiO2 nanoparticles were used as nano-additives to establish a soybean oil-cellulose paper oil-paper insulation model, and the effect of amino-modified SiO2 nanoparticles on micro-water diffusion in oil-paper insulation systems was systematically studied. Simulation experiments show that amino-modified SiO2 nanoparticles can effectively delay the diffusion of water molecules in oil-paper insulation. As the temperature rises, compared with unmodified SiO2 nanoparticles, the diffusion motion of water molecules in amino-modified SiO2 nanoparticles oil–water model is slower. When the temperature is 383 K, the water molecule diffusion coefficient of the unmodified model is 1.22 times that of the modified model, and amino-modified SiO2 nanoparticles can form special hydrogen bonds with water molecules, preventing water molecules from further diffusing into cellulose paper, breaking the cellulose chain leads to a decrease in mechanical property, and further generating small molecules such as water and acid, which accelerate the aging of oil-paper insulation systems. Indirectly improve the electrical performance and aging performance of oil-paper insulation.

Modification of Bulk Density, Flow Property and Crystallinity of Microcrystalline Cellulose Prepared from Waste Cotton.

The most affordable type of tablet is the immediately compressible tablet, which uses microcrystalline cellulose (MCC), a popular pharmaceutical excipient, as a filler or binder. To make it compatible with different active drugs and excipients, we tried to change some physical properties of the MCC. In the current study, we used a chelating agent to pretreat the waste cotton before pulping, bleaching, and finally, hydrochloric acid degradation with a concentration of 2N at 100 °C temperature for 20 min to prepare MCC. The prepared MCC was treated with different concentrations of sodium hydroxide at room temperature or at -20 °C followed by precipitation with hydrochloric acid or ethanol with complete washing with distilled water till neutralization. Evaluation of the degree of polymerization (DP) and FT-IR spectrum confirm the identity of the microcrystalline cellulose. The DP was found to be 216. The bulk density of the unmodified MCC was 0.21 while that of modified MCC varied from 0.253 to 0.594. The modified MCC powder showed good flow properties compared to the unmodified MCC as evaluated by the Hausner index, Carr's index and the angle of repose. The scanning electron microscopy (SEM) of the MCC revealed that the rod shape has been changed to an oval shape due to treatment with sodium hydroxide at -20 °C. The X-ray crystallographic (XRD) analysis indicated that the unmodified MCC and standard MCC showed the crystallinity index (CrI) value of 86.82% and 87.63%, respectively, while the value ranges from 80.18% to 60.7% among the modified MCC powder. The differences in properties of the MCC might be due to the variation of rearrangement of the cellulose chain among the MCC particles due to treatment with different concentrations of a base at different temperatures and precipitation environments. This has enabled us to prepare MCC with different properties which might be compatible with different drugs.

Structure of Cellulose Ether Affected by Ionic Surfactant and Solvent: A Small-Angle Neutron Scattering Investigation.

Polysaccharides and their derivatives are commonly used in pharmaceutical and agricultural formulations as rheology modifiers. Their performance is related to their conformation in solution, which in turn is affected by other ingredients present in the formulation. This study focuses on modulating the conformation of relatively rigid cellulose chains in aqueous solutions. In particular, we have investigated the nonionic cellulose derivative ethyl(hydroxyethyl)cellulose (EHEC) in water in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) and/or ethanol acting as modulating agents. We have used small angle neutron scattering (SANS) with contrast variation to determine the EHEC chain conformation in the presence of (but not masked by) ethanol and SDS. In dilute and semidilute aqueous solutions, EHEC exhibits worm-like chain conformation due to the rigid cellulose backbone. Addition of ethanol does not impact the polymer conformation to a great extent. Addition of SDS alters the EHEC chain conformation, resulting in polyelectrolyte-like scattering behavior due to repulsive interactions between bound charged micelles which show similar structure as the free SDS micelles in solution (in the absence of polymers). Ethanol affects the polymer + surfactant system primarily by acting on the surfactant (bound on polymer) which, in turn, affects the polymer conformation. At higher ethanol concentrations (20 wt %), EHEC regains the worm-like chain conformation because of the detachment of the bound SDS micelles. To the best of our knowledge, this is the only study providing details on chain conformation of the rigid polymer EHEC in dilute or semidilute aqueous solutions in the presence of surfactant and alcohol and one of very few papers utilizing SANS for the characterization of polymer + surfactant + water + alcohol interactions. Such fundamental understanding of interactions and structure in multicomponent mixtures supports the design of industrial formulations.

Strong, hydrophobic, and transparent wood film decorated with MXene/silver nanowire for electromagnetic interference shielding and electrothermal conversion

Facing the continuous development and expansion of electronic devices and consequently increasing severe electromagnetic pollution, new requirements are put forward for electromagnetic interference (EMI) shielding materials, such as high transparency, mechanically robust, and flexibility. However, developing bio-based electromagnetic shielding materials that meet the above requirements remains challenging. Herein, a bio-based transparent wood prepared by delignification and TEMPO-mediated oxidation was used as the substrate, on which a durable hybrid conductive network containing MXene, silver nanowire (AgNW), and hydrophobic regents was assembled to prepare the multifunctional transparent film. The EMI shielding effect value of the obtained hydrophobic MXene/AgNW-decorated transparent wood (H-MATW) film was 31.5 dB with a corresponding transparency of 31.7%, which ascribing to excellent electroconductivity of the MXene/AgNW hybrid conductive network. Moreover, the tensile strength of H-MATW is as high as 406.5 MPa, attributed to the dense structure and strong hydrogen bonds between the cellulose chains in the transparent wood substrate. Furthermore, it exhibited tunable and low-pressure driving electrothermal conversion performance, reaching a temperature of 91 °C at only 4 V voltage. This work reports on bio-based candidate EMI shielding transparent film that can be used in visual windows and smart devices, providing a new pathway for developing flexible EMI shielding and electrothermal conversion materials.

First-Principles Insights on the Bonding Mechanism and Electronic Structure of SWCNT and Oxygenated-SWCNT Functionalized by Cellulose Biopolymer

Here, we report the bonding mechanism and electronic structure of single-walled carbon nanotube and oxygenated single-walled carbon nanotube functionalized by cellulose chain using first-principles density functional theory. Analysis of the optimized molecular configuration and charge redistribution of the nanohybrid indicates that the cellulose chain binds with the prototype single-walled carbon nanotube and oxygenated single-walled carbon nanotube via physisorption. The cellulose chain adsorption on the single-walled carbon nanotube preserved its electronic structure. On the other hand, the electronic structure of the oxygenated single-walled carbon nanotube and cellulose complex reveals that the electronic states of the cellulose tend to populate in the forbidden gap, thus, lowering the bandgap of the overall complex. The electronic structure of the complex can be considered as the superposition of its constituents in which no significant hybridization of the orbital characters is observable. The findings confirm that cellulose is indeed suitable for the non-covalent functionalization of single-walled carbon nanotubes and provide new insights into the electronic structure of the oxygenated single-walled carbon nanotube/cellulose complex.

Facile Fabrication of Fluorescent Cellulose with Aggregation‐Induced Emission Characteristic in a CO2 Switchable Solvent

AbstractFabrication of fluorescent cellulose with aggregation‐induced emission (AIE) characteristics is usually achieved by grafting tetraphenylethylene (TPE) to the cellulose backbone using TPE derivatives with highly active functional groups such as carboxylic, isothiocyanate, and alkynyl groups. However, besides the complicated synthetic routes of these TPE derivatives, conversion of hydroxyl groups in the cellulose chain to more reactive groups such as amine or azide groups is usually involved, and the resulting products have a degree of substitution (DS) of TPE lower than 0.08. Herein, a facile one‐pot strategy for the grafting of a TPE group to the cellulose backbone with high DS of up to 0.22 in a CO2 switchable solvent under mild reaction conditions is reported. The hydroxyl groups in the cellulose are in situ converted to cellulose carbonate intermediately during the dissolution step. Subsequently, nucleophilic substitution between the intermediate and a halogenated TPE derivative with bromine atom as leaving group is carried out to achieve the effective grafting of TPE. The synthetic route for this promising TPE derivative is much more convenient than those of TPE derivatives reported in previous studies. This work suggests a new and facile pathway for the synthesis of high‐emission fluorescent cellulose with AIE functionality.

Wide-range tunable phosphorescence emission in cellulose-based materials enabled by complementary-color phosphors

Developing color-tunable pure organic room-temperature phosphorescent (RTP) materials based on biopolymers is of great significance for efficient utilization of natural resources, yet still challenging. Herein, tunable multicolor phosphorescence emission, including white-light, is achieved in cellulose-based RTP materials by co-organizing complementary cyan and red organic phosphors into the strong hydrogen-bonding networks of cellulose. The non-radiative transition of phosphors can be effectively suppressed by the high density of hydrogen bonding among the cellulose chains as well as the covalent interaction. The difference in optical properties between the two phosphors enables the adjustment of the phosphorescence emission color of the material from green to cyan, white and then red. It is demonstrated that the designed material can be used as versatile inks for pattern drawing and information encryption, with favorable multicolor emission and excellent aqueous processability. Therefore, considering the biodegradability and sustainability of cellulose materials, cellulose-based RTP has enormous potential in advanced anti-counterfeiting and information encryption as eco-friendly phosphorescent inks and coatings.

Impact of hemicelluloses and crystal size on X-ray scattering from atomistic models of cellulose microfibrils

X-ray scattering methods allow efficient characterization of cellulosic materials, but interpreting their results is challenging. By creating molecular dynamics models of cellulose microfibrils and calculating the scattering from them, we investigated how different properties of the structures affect their scattering intensities. We studied the effects of hemicelluloses and crystal size on small-angle and wide-angle X-ray scattering (SAXS, WAXS). Microfibril models with and without surface-bound hemicelluloses were built based on the chemical composition of spruce secondary cell walls. The effect of fibril size was investigated by comparing the scattering from fibrils with 14 to 40 cellulose chains. The hemicelluloses appeared in the SAXS region as an increase in the fibril radius and as a clear contribution of a shell around the fibril. The hemicelluloses also increased the crystal size as determined from the broadening of the 200 diffraction peak of cellulose textrm{I}_upbeta. The SAXS and WAXS analysis provided consistent estimates for the size of the microfibrils, and their special features and challenges were discussed. In particular, the results of 18-chain microfibrils were consistent with prior experimental results. Carrying out the simulations in wet and dry environments had the most pronounced effect on fibrils with a hemicellulose coating. Twisting of the fibril had very little impact on most properties, except for a minor effect on the WAXS peaks. The results allow for more correct interpretation of experimental scattering results, leading to more accurate descriptions of microfibril structures in natural and processed cellulosic materials.

Enhanced Dielectric Properties of All-Cellulose Composite Film via Modulating Hydroxymethyl Conformation and Hydrogen Bonding Network.

Cellulose-based dielectrics with attractive dielectric performance are promising candidates to develop eco-friendly electrostatic energy storage devices. Herein, all-cellulose composite films with superior dielectric constant were fabricated by manipulating the dissolution temperature of native cellulose, where we revealed the relationship among the hierarchical microstructure of the crystalline structure, the hydrogen bonding network, the relaxation behavior at a molecular level, and the dielectric performance of the cellulose film. The coexistence of cellulose I and cellulose II led to a weakened hydrogen bonding network and unstable C6 conformations. The increased mobility of cellulose chains in the cellulose I-amorphous interphase enhanced the dielectric relaxation strength of side groups and localized main chains. As a result, the as-prepared all-cellulose composite films exhibited a fascinating dielectric constant of as high as 13.9 at 1000 Hz. This work proposed here provides a significant step toward fundamentally understanding the dielectric relaxation of cellulose, thus developing high-performance and eco-friendly cellulose-based film capacitors.

Optimized Lytic Polysaccharide Monooxygenase Action Increases Fiber Accessibility and Fibrillation by Releasing Tension Stress in Cellulose Cotton Fibers.

Lytic polysaccharide monooxygenase (LPMO) enzymes have recently shaken up our knowledge of the enzymatic degradation of biopolymers and cellulose in particular. This unique class of metalloenzymes cleaves cellulose and other recalcitrant polysaccharides using an oxidative mechanism. Despite their potential in biomass saccharification and cellulose fibrillation, the detailed mode of action of LPMOs at the surface of cellulose fibers still remains poorly understood and highly challenging to investigate. In this study, we first determined the optimal parameters (temperature, pH, enzyme concentration, and pulp consistency) of LPMO action on the cellulose fibers by analyzing the changes in molar mass distribution of solubilized fibers using high performance size exclusion chromatography (HPSEC). Using an experimental design approach with a fungal LPMO from the AA9 family (PaLPMO9H) and cotton fibers, we revealed a maximum decrease in molar mass at 26.6 °C and pH 5.5, with 1.6% w/w enzyme loading in dilute cellulose dispersions (100 mg of cellulose at 0.5% w/v). These optimal conditions were used to further investigate the effect of PaLPMO9H on the cellulosic fiber structure. Direct visualization of the fiber surface by scanning electron microscopy (SEM) revealed that PaLPMO9H created cracks on the cellulose surface while it attacked tension regions that triggered the rearrangement of cellulose chains. Solid-state NMR indicated that PaLPMO9H increased the lateral fibril dimension and created novel accessible surfaces. This study confirms the LPMO-driven disruption of cellulose fibers and extends our knowledge of the mechanism underlying such modifications. We hypothesize that the oxidative cleavage at the surface of the fibers releases the tension stress with loosening of the fiber structure and peeling of the surface, thereby increasing the accessibility and facilitating fibrillation.

Insight into etherification of 1,3-dimethylol-2-imidazolidinone with the primary alcohols and the hydroxyl groups of cellulose chain (n = 1–4) in acidic condition

Etherification of 1,3-dimethylol-2-imidazolidinone (DMEU) with the primary alcohols and the hydroxyl groups of cellulose chain (n = 1–4) in acidic condition were probed in both gas phase and water solvent by using the Onsager model and polarized continuum model (PCM). Geometry and energy of reactants, products, intermediate complexes, carbocation intermediate, and transition state (TS) structures were calculated by using the methods of MP2, B3LYP, PM3MM at the basis sets of 6-311+g (d), 6-311g (d,p). The computational results indicate that the etherification adheres to unimolecular nucleophilic substitution (SN1) mechanism; reactants and products can form the activated complexes with H+ ions in which H+ ions are occupied by the O-atom of CO group in the reactant complex and the product complex. Potential energy surface (PES) of the reaction has the triple-well shape. Effect of substituent R in primary alcohol R-CH2OH (R = H, CH3, CH2CH3, CH2OCH3, CH2F) on the reactivity is significant. The energy barrier of H+ ions releasing step is much higher than those of the activation steps. The calculational data is in the good agreement with the experimental data in the literature.

Molecular Dynamics Simulation of the Effect of Low Temperature on the Properties of Lignocellulosic Amorphous Region

In this paper, a molecular model of cellulose amorphous region-water molecule was developed using Materials Studio software by applying the molecular dynamics method. The effect of low temperature on the properties of the lignocellulosic amorphous region, the main component of wood, was investigated in an attempt to explain the macroscopic property changes from a microscopic perspective and to provide a theoretical basis for the safe use of wood and wood products in low-temperature environments and other related areas of research. Dynamic simulations were carried out at 20 °C, 0 °C, −30 °C, −70 °C, −110 °C and −150 °C for the NPT combinations to obtain the energy, volume, density, and hydrogen bonding change trends of their models, respectively. The changes in the microstructure of the water molecule–cellulose amorphous region model were analyzed, and the mechanical properties were calculated. The results showed that the interaction between the amorphous cellulose region and water molecules was enhanced as the temperature decreased, the density of the models increased, and the volume decreased. The number of total hydrogen bonds and the number of hydrogen bonds between water molecule–cellulose chains increased for each model, and the decrease in temperature made the cellulose molecular activities weaker. The values of G, E, and K increased with the decrease in temperature, and K/G decreased with the decrease in temperature. It shows that the decrease in temperature is beneficial to enhance the mechanical properties of the amorphous region of cellulose and increases the stiffness of the material. However, the toughness and plasticity decrease when the temperature is too low.

Facile synthesis of porous cellulose aerogel beads with tunable core–shell microstructures and physical properties

Cellulose aerogel beads (CABs) have emerged as advanced biomaterials with numerous engineering applications, including chromatography and drug release. In this study, porous core–shell CABs were synthesized using a dilute ethanol solution-substitution-assisted freeze-drying. The formation mechanism of the CABs and the effect of ethanol concentration on the core–shell microstructures and physical properties were investigated. Cellulose hydrogel beads (CHBs) were formed through the exchange/neutralization of acetic acid with tetraethylammonium hydroxide (TEAOH)/urea. The cellulose chains dissolved in the cellulose–TEAOH/urea droplets regenerated from the edge to the inside of the droplet in an acetic acid bath. Notably, adding ethanol at a concentration of 10% before freeze-drying can result in core–shell CABs with non-obvious structural shrinkage, large particle size, uniform pores, and high porosity. Ethanol molecules induce ice crystal growth to form more uniform ice crystals during the freezing process. Additionally, by altering the TEAOH/urea molar ratios and cellulose concentrations of cellulose solutions, well-shaped and porous CABs were prepared, demonstrating the feasibility and availability of dilute ethanol solution-assisted freeze-drying. Consequently, the as-fabricated CABs had a dense micro-shell (1–9 μm) and loose millimetric-core with anisotropic pores (2–6 μm), exhibiting low density (0.06–0.09 g/cm3), high porosity (87.0–91.5%), and noteworthy thermal stability.