Molecular Dynamics Simulations of Bulk Native Crystalline and Amorphous Structures of Cellulose

Differences in protein structural regions that impact functional specificity in GT2 family β-glucan synthases

Most cell wall and secreted β-glucans are synthesised by the CAZy Glycosyltransferase 2 family (www.cazy.org), with different members catalysing the formation of (1,4)-β-, (1,3)-β-, or both (1,4)- and (1,3)-β-glucosidic linkages. Given the distinct physicochemical properties of each of the resultant β-glucans (cellulose, curdlan, and mixed linkage glucan, respectively) are crucial to their biological and biotechnological functions, there is a desire to understand the molecular evolution of synthesis and how linkage specificity is determined. With structural studies hamstrung by the instability of these proteins to solubilisation, we have utilised in silico techniques and the crystal structure for a bacterial cellulose synthase to further understand how these enzymes have evolved distinct functions. Sequence and phylogenetic analyses were performed to determine amino acid conservation, both family-wide and within each sub-family. Further structural analysis centred on comparison of a bacterial curdlan synthase homology model with the bacterial cellulose synthase crystal structure, with molecular dynamics simulations performed with their respective β-glucan products bound in the trans-membrane channel. Key residues that differentially interact with the different β-glucan chains and have sub-family-specific conservation were found to reside at the entrance of the trans-membrane channel. The linkage-specific catalytic activity of these enzymes and hence the type of β-glucan chain built is thus likely determined by the different interactions between the proteins and the first few glucose residues in the channel, which in turn dictates the position of the acceptor glucose. The sequence-function relationships for the bacterial β-glucan synthases pave the way for extending this understanding to other kingdoms, such as plants.

Mechanical properties of cellulose aerogels and cryogels

Highly porous and lightweight cellulose materials were prepared via dissolution-coagulation and different drying routes. Cellulose of three different molecular weights was dissolved in an ionic liquid/dimethyl sulfoxide mixture. Drying was performed either with supercritical CO2 resulting in "aerogels", or via freeze-drying resulting in "cryogels". The influence of cellulose molecular weight, concentration and drying method on the morphology, density, porosity and specific surface area was determined. The mechanical properties of cellulose cryogels and aerogels under uniaxial compression were studied in detail and analyzed in the view of existing models developed for porous materials. It was demonstrated that the Poisson's ratio of cellulose aerogels is not equal to zero, contrary to what is usually reported in the literature, but decreases with an increase in density. Compressive modulus and yield stress of cryogels turned out to be higher than those of aerogels taken at the same density. This was interpreted by the different morphology of the porous materials studied.

Improvement of the Space Charge Suppression and Hydrophobicity Property of Cellulose Insulation Pressboard by Surface Sputtering a ZnO/PTFE Functional Film

Oil-impregnated cellulose insulation polymer (oil-paper/pressboard insulation) has been widely used in power transformers. Establishing effective ways of improving the physical and chemical properties of the cellulose insulation polymer is currently a popular research topic. In order to improve the charge injection inhibition and hydrophobic properties of the cellulose insulation polymer used in power transformers, nano-structure zinc oxide (ZnO) and polytetrafluoroethylene (PTFE) films were fabricated on a cellulose insulation pressboard surface via reactive radio frequency (RF) magnetron sputtering. Before the fabrication of their composite film, Accelrys Materials Studio (MS) software was applied to simulate the interaction between the nanoparticles and cellulose molecules to determine the depositing sequence. Simulation results show that the ZnO nanoparticle has a better adhesion strength with cellulose molecules than the PTFE nanoparticle, so ZnO film should be sputtered at first to fabricate the ZnO/PTFE composite film for better film quality. The sputtered, thin films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The space charge injection behavior and the hydrophobicity performance of the untreated pressboard; and the cellulose insulation pressboard with sputtered nano-structure ZnO, PTFE, and the ZnO/PTFE functional films were compared with each other. X-ray photoelectron spectroscopy results showed that ZnO, PTFE, and ZnO/PTFE functional films were all successfully fabricated on the cellulose insulation pressboard surface. Scanning electron microscopy and XRD results present the nano-structure of the sputtered ZnO, PTFE, and ZnO/PTFE functional films and their amorphous states, respectively. The ZnO/PTFE composite functional film shows an apparent space charge suppression effect and hydrophobicity. The amount of the accumulated space charge in the pressboard sputtered ZnO/PTFE composite functional film decreased by about 40% compared with that in untreated cellulose insulation pressboard, and the water contact angle (WCA) increased from 0° to 116°.

Multilayer Density Analysis of Cellulose Thin Films

An approach for the multilayer density analysis of polysaccharide thin films at the example of cellulose is presented. In detail, a model was developed for the evaluation of the density in different layers across the thickness direction of the film. The cellulose thin film was split into a so called "roughness layer" present at the surface and a "bulk layer" attached to the substrate surface. For this approach, a combination of multi-parameter surface plasmon resonance spectroscopy (SPR) and atomic force microscopy (AFM) was employed to detect changes in the properties, such as cellulose content and density, thickness and refractive index, of the surface near layer and the bulk layer. The surface region of the films featured a much lower density than the bulk. Further, these results correlate to X-ray reflectivity studies, indicating a similar layered structure with reduced density at the surface near regions. The proposed method provides an approach to analyse density variations in thin films which can be used to study material properties and swelling behavior in different layers of the films. Limitations and challenges of the multilayer model evaluation method of cellulose thin films were discussed. This particularly involves the selection of the starting values for iteration of the layer thickness of the top layer, which was overcome by incorporation of AFM data in this study.

3D-Printed Anti-Fouling Cellulose Mesh for Highly Efficient Oil/Water Separation Applications

The ability of additive manufacturing to print mesh structure was exploited to fabricate highly efficient filtration meshes for oil/water separation applications. Through Direct Ink Writing (DIW) technique, pure cellulose acetate with a mesh architecture can be created easily, using cellulose acetate/ethyl acetate solution as the ink and simply drying off the solvent in ambient conditions. Besides conventional mesh structures, more complex structures can be fabricated in order to manipulate the pore size and hence tune the separation properties of the mesh. The superhydrophilic 3D-printed cellulose meshes are able to achieve a high separation efficiency of >95% as long as the average pore size is smaller than 280 μm. More importantly, the mesh that possesses an unconventional complex structure boasts a separation efficiency of ∼99% while maintaining a high water flux of ∼160 000 Lm^2-h^-1. The 3D-printed cellulose meshes are also able to separate oil substances of a wide range of viscosity, from highly viscous PDMS (∼97 cP) to nonviscous cyclohexane (∼1 cP) and are chemically resistant to extreme acidic and alkaline conditions. Moreover, the 3D-printed cellulose meshes also possess antioil-fouling/self-cleaning ability, which makes its surfaces resilient to contamination. In addition, the 3D-printed meshes do not suffer from surface inhomogeneity and interfacial adhesion issues as compared to the usual coated meshes. Such a robust yet practical system is highly applicable for highly efficient oil-water separation applications.

An aggregated understanding of cellulase adsorption and hydrolysis for ball-milled cellulose

This study evaluated the effects of physicochemical properties of a series of ball-milled cellulose on cellulase adsorption and glucose yield. The relationship between cellulase adsorption and initial hydrolysis rate was also discussed. We found that hydrophobicity and surface charge are the key factors affecting cellulase adsorption on ball-milled cellulose. The results demonstrated that glucose yield had a positive correlation with specific surface area, while showed a negative correlation with particle size, degree of polymerization and crystallinity. Among these properties, specific surface area and crystallinity are the key factors affecting glucose yield. As ball milling progressed, cellulose showed lower enzyme adsorption capacity/amount of bound enzyme during initial stage of hydrolysis, but had higher initial hydrolysis rate. The enhanced rate is attributed to the fact that the amorphous region produced by ball milling reduces the free energy required for decrystallization thus increases the catalytic efficiency of the bound enzyme.

Molecular Simulation on the Thermal Stability of Meta-Aramid Insulation Paper Fiber at Transformer Operating Temperature

The influence of the thermal field of a transformer during operation on the thermal stability of meta-aramid insulation paper was studied through molecular dynamics simulations. Models of the crystalline and amorphous regions of meta-aramid fibers were constructed using known parameters. The model of the crystalline area was verified by comparing X-ray diffraction results with experimental data. The reasonableness of the simulation results was judged by the variation of energy, temperature, density, and cell size in relation to the dynamic time. The molecular dynamics simulations revealed that the modulus values in the crystalline regions were two to three times higher than those in the amorphous regions at various temperatures. In addition, the incompressibility, rigidity, deformation resistance, plasticity, and toughness of the crystalline regions were obviously higher than those of amorphous regions, whereas the toughness of the amorphous regions was better than that of the crystalline regions. The mechanical parameters of both the crystalline and amorphous regions of meta-aramid fibers were affected by temperature, although the amorphous regions were more sensitive to temperature than the crystalline regions. The molecular chain motion in the crystalline regions of meta-aramid fibers increased slightly with temperature, whereas that of the amorphous regions was more sensitive to temperature. Analyzing hydrogen bonding revealed that long-term operation at high temperature may destroy the structure of the crystalline regions of meta-aramid fibers, degrading the performance of meta-aramid insulation paper. Therefore, increasing the crystallinity and lowering the transformer operating temperature may improve the thermal stability of meta-aramid insulation paper. However, it should be noted that increasing the crystallinity of insulation paper may lower its toughness. These study results lay a good foundation for further exploration of the ways to improve the performance of meta-aramid insulation paper.

Influence of Polymethylsilsesquioxane Content to the Thermal Stability of Meta-Aramid Fiber Insulation Paper

Polymethylsilsesquioxane (PMSQ) nanoparticles with mass percentages of 0, 2.5, 5.0, 7.2, 9.4 wt %, respectively, were constructed by molecular dynamics methods in this paper. Composite molecular models were established using PMSQ and MPIA (poly-metaphenylene isophthalamide) fiber. The influence of different PMSQ contents on the thermal stability of meta-aramid insulation paper was analyzed from the parameters of mechanical property, interaction energy, and mean square displacement. The results showed that the trend of mechanical properties decreased with the increase of PMSQ content. When the PMSQ content was 2.5 wt %, the mechanical properties of the composited model were the best, which was about 24% higher than that of the unmodified model. From an intermolecular bonding and nonbonding point of view, the energy parameters of composite model with the 2.5 wt % content was better than those of the composite model with other contents. Therefore, it is considered that MPIA can interact better with the 2.5 wt % content PMSQ composite model. When the PMSQ content is 2.5 wt %, the overall chain movement in the composite model is slower than that of the unmodified model, which can effectively inhibit the diffusion movement of the MPIA chain. In general, the thermal stability of composite molecular models MPIA and PMSQ (2.5 wt %) was better improved.

Molecular Dynamics Simulations of Molecular Diffusion Equilibrium and Breakdown Mechanism of Oil-Impregnated Pressboard with Water Impurity

The water molecule migration and aggregation behaviors in oil-impregnated pressboard are investigated by molecular dynamics simulations in combination with Monte Carlo molecular simulation technique. The free energy and phase diagram of H₂O-dodecylbenzene (DDB) and H₂O-cellulose mixtures are calculated by Monte Carlo technique combined with the modified Flory-Huggins model, demonstrating that H₂O molecules can hardly dissolved with infinitesimal content in cellulose system at temperature lower than 650 K, based on which the oil/cellulose layered structure with water impurity representing three-phase coexistence in oil-impregnated pressboard are modeled and performed for molecular dynamics. The molecular dynamics of H₂O/DDB/cellulose three-phase mixture simulating oil-paper insulating system with H₂O impurity indicates that DDB molecules can thermally intrude into the cellulose-water interface so as to separate the water phase and cellulose fiber. The first-principles electronic structure calculations for local region of H₂O/DDB interface show that H₂O molecules can introduce bound states to trap electrons and acquire negative charges, so that they will obtain sufficient energy from applied electric field to break DDB molecular chain by collision, which are verified by subsequent molecular dynamics simulations of H₂O⁻/DDB interface model. The electric breakdown mechanism under higher than 100 kV/m electric field is presented based on the further first-principles calculations of the produced carbonized fragments being dissolved and diffusing in DDB phase. The resulted broken DDB fragments will introduce impurity band between valence and conduction bands of DDB system, evidently decreasing bandgap as to that of conducting materials in their existence space. The conductance channel of these carbonized DDB fragments will eventually be formed to initiate the avalanche breakdown process by the cycle-feedback of injected charge carriers with carbonized channels.

Biopolymer nanofibrils: structure, modeling, preparation, and applications

Biopolymer nanofibrils exhibit exceptional mechanical properties with a unique combination of strength and toughness, while also presenting biological functions that interact with the surrounding environment. These features of biopolymer nanofibrils profit from their hierarchical structures that spun angstrom to hundreds of nanometer scales. To maintain these unique structural features and to directly utilize these natural supramolecular assemblies, a variety of new methods have been developed to produce biopolymer nanofibrils. In particular, cellulose nanofibrils (CNFs), chitin nanofibrils (ChNFs), silk nanofibrils (SNFs) and collagen nanofibrils (CoNFs), as the four most abundant biopolymer nanofibrils on earth, have been the focus of research in recent years due to their renewable features, wide availability, low-cost, biocompatibility, and biodegradability. A series of top-down and bottom-up strategies have been accessed to exfoliate and regenerate these nanofibrils for versatile advanced applications. In this review, we first summarize the structures of biopolymer nanofibrils in nature and outline their related computational models with the aim of disclosing fundamental structure-property relationships in biological materials. Then, we discuss the underlying methods used for the preparation of CNFs, ChNFs, SNF and CoNFs, and discuss emerging applications for these biopolymer nanofibrils.

Chemocatalytic Conversion of Cellulose into Key Platform Chemicals

Chemocatalytic transformation of lignocellulosic biomass to value-added chemicals has attracted global interest in order to build up sustainable societies. Cellulose, the first most abundant constituent of lignocellulosic biomass, has received extensive attention for its comprehensive utilization of resource, such as its catalytic conversion into high value-added chemicals and fuels (e.g., HMF, DMF, and isosorbide). However, the low reactivity of cellulose has prevented its use in chemical industry due to stable chemical structure and poor solubility in common solvents over the cellulose. Recently, homogeneous or heterogeneous catalysis for the conversion of cellulose has been expected to overcome this issue, because various types of pretreatment and homogeneous or heterogeneous catalysts can be designed and applied in a wide range of reaction conditions. In this review, we show the present situation and perspective of homogeneous or heterogeneous catalysis for the direct conversion of cellulose into useful platform chemicals.

Electric Field Intensity Effects on the Microstructural Characteristics Evolution of Methyl Vinyl Silicone Rubber via Molecular Simulation

During ultra high voltage (UHV) transmission, the discharge caused by high intensity electric fields aggravates the aging process of external insulation materials used for composite insulators. The microstructural characteristics of its base material polymer-methyl vinyl silicone rubber-are the key basis for the performance of insulation materials under electric field exposure. Based on molecular dynamics simulations, a molecular model of methyl vinyl silicone rubber was established. Mechanisms influencing the microstructure evolution under electric fields had been studied at the atomic level. The results showed that the initial reaction characteristics of silicone rubber molecules involve the violent vibrated of all the methyl and vinyl atoms, and shortening of the chemical bonds. The neighboring groups were close to each other and generated different amounts of -Si-Si- bonds. This promoted the helical shrinkage of the molecule, and protrusion of the middle of the molecule which presented an inverted U shape. The high electric field greatly reduced the total energy of molecules, and the potential energy in particular was more severely destroyed, resulting in degradation of its structure. Besides, as the electric field intensity increased, the elastic modulus of the molecule gradually increased. It was shown that high electric fields would make the stiffness of silicone rubber become larger, and the brittleness to become stronger, which reduced the mechanical properties of materials, accelerating its aging. The results provide a theoretical basis for establishing the connection between the micro appearance and macro characteristics of materials, as well as reference values for the optimization of base materials used for making composite insulators.

Pharmaceutical Applications of Cellulose Ethers and Cellulose Ether Esters

Cellulose ethers have proven to be highly useful natural-based polymers, finding application in areas including food, personal care products, oil field chemicals, construction, paper, adhesives, and textiles. They have particular value in pharmaceutical applications due to characteristics including high glass transition temperatures, high chemical and photochemical stability, solubility, limited crystallinity, hydrogen bonding capability, and low toxicity. With regard to toxicity, cellulose ethers have essentially no ability to permeate through gastrointestinal enterocytes and many are already in formulations approved by the U.S. Food and Drug Administration. We review pharmaceutical applications of these valuable polymers from a structure-property-function perspective, discussing each important commercial cellulose ether class; carboxymethyl cellulose, methyl cellulose, hydroxypropylcellulose, hydroxypropyl methyl cellulose, and ethyl cellulose, and cellulose ether esters including hydroxypropyl methyl cellulose acetate succinate and carboxymethyl cellulose acetate butyrate. We also summarize their syntheses, basic material properties, and key pharmaceutical applications.

Changes in the physicochemical structure and pyrolysis characteristics of wheat straw after rod-milling pretreatment

Pyrolysis is increasingly used for raw biomass conversion. In this study, the effects of rod-milling pretreatment (RMP) on the physicochemical properties and pyrolysis characteristics of wheat straw (WS) was found. The mechanism behind these changes was further analyzed. RMP appreciably reduced the particle size and cellulose crystallinity, and increased the specific surface area and pore volume of WS. Under RMP, with an increasing conversion rate α, the activation energy E was expressed as a para-curve, whereas it was expressed as a tangent curve for samples that underwent hammer-milling pretreatment (HMP). At the same α, the thermal degradation temperature for RMP was lower than that for HMP. The E value clearly decreased with RMP, and increased following a wave-like pattern with increased rod-milling strength (RMS). The lowest E value (118.69 or 108.97 kJ/mol) was obtained with a milling time of 60 min. Hence, RMP is an environmental-friendly and effective method for improving the efficiency of pyrolysis.

Liquid Water Confined in Cellulose with Variable Interfacial Hydrophilicity

We investigate liquid water confined within nanoscale cellulose slabs by means of molecular dynamics simulations. Depending on the construction of the cellulose–water interface, two different surface structures with distinct levels of hydrophilicity are exposed to the water. The different philicities are reflected in the response of the water phase to this geometric confinement, both in terms of the density profile and in the strength of the aqueous hydrogen bonding network. At the smooth surface cut along the (010) axis of the cellulose crystal, water shows typical properties of a hydrophilic confinement: the density shows fluctuations that disappear further away from the wall, the water molecules orient themselves and the coordination numbers increases at the interface. As a consequence, the water becomes “harder” at the interface, with a considerably increased local ordering. At the zigzag-shaped surface along the (111) axis, the degree of hydrophilicity is reduced, and only small effects can be seen: the density shows weak fluctuations, and the orientation of the water molecules is closer to that of bulk water than to the smooth surface. The local coordination numbers remains constant over the whole confinement. Our work shows that the nature of the exposed cellulose interface has a strong influence on how the structure of adjacent water is modified. The different ways of surface construction yield distinct degrees of hydrophilicity and spatial accessibility regarding the hydrogen bond network, resulting in a notably different interfacial water structure.

Computational Thermomechanical Properties of Silica⁻Epoxy Nanocomposites by Molecular Dynamic Simulation

Silica⁻epoxy nanocomposite models were established to investigate the influence of silane coupling agent on the structure and thermomechanical properties of the nanocomposites through molecular dynamics simulation. Results revealed that incorporating silica nanoparticles into a polymer matrix could improve thermomechanical properties of the composites and increase their glass transition temperature and thermal conductivity. Their thermomechanical properties were further enhanced through silane coupling agent modification on the surface of fillers. Compared with that of pure epoxy, the glass transition temperatures of the silica⁻epoxy composites with grafting ratios of 5% and 10% increased by 17 and 28 K, respectively. The thermal conductivities of the two models at room temperature respectively increased by 60.0% and 67.1%. At higher temperature 450 K, thermal conductivity of the nanocomposite model with a high grafting ratio of 10% demonstrated a considerable increase of approximately 50% over the pure epoxy resin (EP) model. The elastic and shear modulus of the nanocomposite models decreased at temperatures below their glass transition temperatures. These observations were further addressed in the interpretation from three aspects: segmental mobility capability, radial distribution function, and free volume fraction. Our computational results are largely consistent with existing experimental data, and our simulation model got fully validated.

The Effect of Moisture on Cellulose Nanocrystals Intended as a High Gas Barrier Coating on Flexible Packaging Materials

Cellulose nanocrystals (CNCs) exhibit outstanding gas barrier properties, which supports their use as a biobased and biodegradable barrier coating on flexible food packaging materials. As highly hydrophilic biopolymers, however, CNCs have a strong sensitivity to water that can be detrimental to applications with fresh foods and in moist conditions due to the loss of barrier properties. In this work, the oxygen and water vapor permeability of polyethylene terephthalate (PET) films coated with CNCs obtained from cotton linters were measured at varying levels of relative humidity, both in adsorption and desorption, and from these data, the diffusion and solubility coefficients were estimated. Therefore, the characterization of CNCs was aimed at understanding the fundamentals of the water-CNCs interaction and proposing counteractions. The CNCs’ moisture absorption and desorption isotherms at 25 °C were collected in the range of relative humidity 0–97% using different techniques and analyzed through GAB (Guggenheim-Anderson-de Boer) and Oswin models. The effects of moisture on the water status, following the freezable water index, and on the crystal structure of CNCs were investigated by Differential Scanning Calorimetry and by X-ray Powder Diffraction, respectively. These findings point to the opportunity of coupling CNCs with hydrophobic layers in order to boost their capabilities as barrier packaging materials.

High yield conversion of cellulosic biomass into 5-hydroxymethylfurfural and a study of the reaction kinetics of cellulose to HMF conversion in a biphasic system

Biphasic dehydration of cellulosic biomass into remarkable yield of HMF can be achieved via mechanocatalysis and fractionation treatment.

Adhesive and Reinforcing Properties of Soluble Cellulose: A Repulpable Adhesive for Wet and Dry Cellulosic Substrates

This work reports, for the first time, the excellent performance of an aqueous alkaline solution of cellulose as an adhesive for wet and dry cellulosic substrates. Uniaxial tensile tests of filter paper and sulfite writing paper strips bonded with this adhesive (5% cellulose and 7% NaOH aqueous solution) show that failure never occurs in the joints but always in the pristine substrate areas, except in butt joint samples prepared with sulfite paper. Tensile test also shows that paper impregnated with cellulose solution is stronger than the original substrate. X-ray microtomography and scanning electron microscopy reveal that dissolved cellulose fills the gaps between paper fibers, providing a morphological evidence for the mechanical interlocking adhesion mechanism, while scanning probe techniques provide a sharp view of different domains in the joints. Additionally, bonded paper is easily reconverted to pulp, which facilitates paper reprocessability, solving a well-known industrial problem related to deposition of adhesive aggregates (stickies) on the production equipment.

Poroelastic model for adsorption-induced deformation of biopolymers obtained from molecular simulations

Molecular simulation of adsorption of water molecules in nanoporous amorphous biopolymers, e.g., cellulose, reveals nonlinear swelling and nonlinear mechanical response with the increase in fluid content. These nonlinearities result from hydrogen bond breakage by water molecules. Classical poroelastic models, employing porosity and pore pressure as basic variables for describing the "pore fluid," are not adequate for the description of these systems. There is neither a static geometric structure to which porosity can sensibly be assigned nor arrangements of water molecules that are adequately described by giving them a pressure. We employ molar concentration of water and chemical potential to describe the state of the "pore fluid" and stress-strain as mechanical variables. A thermodynamic description is developed using a model energy function having mechanical, fluid, and fluid-mechanical coupling contributions. The parameters in this model energy are fixed by the output of the initial simulation and validated with the results of further simulation. The poroelastic properties, e.g., swelling and mechanical response, are found to be functions both of the molar concentration of water and the stress. The basic fluid-mechanical coupling coefficient, the swelling coefficient, depends on the molar concentration of water and stress and is interpreted in terms of porosity change and solid matrix deformation. The difference between drained and undrained bulk stiffness is explained as is the dependence of these moduli on concentration and stress.

Molecular Origin of Strength and Stiffness in Bamboo Fibrils

Bamboo, a fast-growing grass, has a higher strength-to-weight ratio than steel and concrete. The unique properties of bamboo come from the natural composite structure of fibers that consists mainly of cellulose microfibrils in a matrix of intertwined hemicellulose and lignin called lignin-carbohydrate complex (LCC). Here, we have used atomistic simulations to study the mechanical properties of and adhesive interactions between the materials in bamboo fibers. With this aim, we have developed molecular models of lignin, hemicellulose and LCC structures to study the elastic moduli and the adhesion energies between these materials and cellulose microfibril faces. Good agreement was observed between the simulation results and experimental data. It was also shown that the hemicellulose model has stronger mechanical properties than lignin while lignin exhibits greater tendency to adhere to cellulose microfibrils. The study suggests that the abundance of hydrogen bonds in hemicellulose chains is responsible for improving the mechanical behavior of LCC. The strong van der Waals forces between lignin molecules and cellulose microfibril is responsible for higher adhesion energy between LCC and cellulose microfibrils. We also found out that the amorphous regions of cellulose microfibrils are the weakest interfaces in bamboo fibrils. Hence, they determine the fibril strength.

Enhanced materials from nature: nanocellulose from citrus waste

Nanocellulose is a relatively inexpensive, highly versatile bio-based renewable material with advantageous properties, including biodegradability and nontoxicity. Numerous potential applications of nanocellulose, such as its use for the preparation of high-performance composites, have attracted much attention from industry. Owing to the low energy consumption and the addition of significant value, nanocellulose extraction from agricultural waste is one of the best alternatives for waste treatment. Different techniques for the isolation and purification of nanocellulose have been reported, and combining these techniques influences the morphology of the resultant fibers. Herein, some of the extraction routes for obtaining nanocellulose from citrus waste are addressed. The morphology of nanocellulose was determined by Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM), while cellulose crystallinity indexes (CI) from lyophilized samples were determined using solid-state Nuclear Magnetic Resonance (NMR) and X-Ray Diffraction (XRD) measurements. The resultant nanofibers had 55% crystallinity, an average diameter of 10 nm and a length of 458 nm.

Effect of Moisture on Physicochemical Properties of Cellulose Studied by Molecular Dynamics

In this work, the physicochemical property and its Effect of hydrous amorphous cellulose has been studied using molecular dynamics. Both intramolecular and intermolecular hydrogen bonds in cellulose molecules decrease with increasing water content, directly leading to the decline of cellulose cohesive energy density, solubility parameters, and mechanical parameters. High water content in amorphous cellulose gives bigger interchain distance of cellulose molecules, indicating that the intermolecular interaction of cellulose molecules is weakened greatly by water.

The hygroscopic power of amorphous cellulose: a modeling study

The relationship between cellulose and water was studied by building dense amorphous cellulose models and subjecting them to increasing moisture contents. When starting from completely dry cellulose, the first diffused water molecules were essentially individualized and hydrogen bonded exclusively to the O6 and O2 hydroxyl groups of cellulose. Upon continued hydration increase, the hydroxyl at O3 and then the acetal oxygens of cellulose also started to attract the upcoming water molecules, which were no longer isolated. They progressively became aggregated, first into clusters and then at high hydration content, into continuous capillary channels. A benefit of this study was to allow predicting a number of physical parameters of amorphous cellulose and their variation under hydration. With some parameters, the calculated values matched rather well the experimental literature determinations. This was the case for the hydration dependence of Tg, the stereoselectivity of the cellulose oxygen atoms for water molecules, together with the diffusion coefficients of water into cellulose. An estimate of the hygro-expansion of amorphous cellulose was provided.

Entropically favored adsorption of cellulosic molecules onto carbon materials through hydrophobic functionalities

Carbon-based materials have attracted interest as high-performance catalysts for the aqueous-phase conversion of cellulose. The adsorption of β-glucans plays a crucial role in the catalytic performance of carbons, although the primary driving force and details of the adsorption process remain unclear. This study demonstrates that adsorption occurs at hydrophobic sites on the carbon surface and that hydrophilic groups are not involved. Analysis of adsorption temperature dependence also reveals that the entropy change associated with adsorption is positive. Our results indicate that adsorption occurs by entropically driven hydrophobic interactions in addition to CH-π hydrogen bonding. These same CH-π hydrogen bonds are also confirmed by DFT calculations. The adsorption of β-glucans on carbons is significantly stronger than the affinity between β-glucans. The adsorption equilibrium constants of β-glucans on carbons increase exponentially with increasing degrees of polymerization, which supports the theory of strong interactions between the carbon and the long β-glucans found in cellulose.

Molecular dynamics simulations of the adhesion of a thin annealed film of oleic acid onto crystalline cellulose

Molecular dynamics simulations were used to characterize the wetting behavior of crystalline cellulose planes in contact with a thin oily film of oleic acid. Cellulose crystal planes with higher molecular protrusions and increased surface area produced stronger adhesion if compared to other crystal planes due to enhanced wetting and hydrogen bonding. The detailed characteristics of crystal plane features and the contribution of directional hydrogen bonding was investigated. Similarly, oleophilicity of the cellulose planes increased with the increase in surface roughness and number of directional hydrogen bonds. These results correlate with conclusions drawn from experimental studies such as adhesion of an ink vehicle on cellulose surface.