Thermal Response in Crystalline Iβ Cellulose: A Molecular Dynamics Study

Dynamic Thermostable Cellulosic Triboelectric Materials from Multilevel-Non-Covalent Interactions

Triboelectric materials present great potential for harvesting huge amounts of dispersed energy, and converting them directly into useful electricity, a process that generates power more sustainably. Triboelectric nanogenerators (TENGs) have emerged as a technology to power electronics and sensors, and it is expected to solve the problem of energy harvesting and self-powered sensing from extreme environments. In this paper, a high-temperature-resistant triboelectric material is designed based on multilevel non-covalent bonding interactions, which achieves an ultra-high surface charge density of 192 µC m-2 at high temperatures. TENGs based on the triboelectric material exhibit more than an order of magnitude higher power output (2750 mW m-2 at 200 °C) than the existing devices at high temperatures. These remarkable properties are achieved based on enthalpy-driven molecular assembly in highly unbonded states. Thus, the material maintains bond strength and ultra-high surface charge density in entropy-dominated high-temperature environments. This molecular design concept points out a promising direction for the preparation of polymers with excellent triboelectric properties.

Cellulose-Hemicellulose-Lignin Interaction in the Secondary Cell Wall of Coconut Endocarp

The coconut shell consists of three distinct layers: the skin-like outermost exocarp, the thick fibrous mesocarp, and the hard and tough inner endocarp. In this work, we focused on the endocarp because it features a unique combination of superior properties, including low weight, high strength, high hardness, and high toughness. These properties are usually mutually exclusive in synthesized composites. The microstructures of the secondary cell wall of the endocarp at the nanoscale, in which cellulose microfibrils are surrounded by hemicellulose and lignin, were generated. All-atom molecular dynamics simulations with PCFF force field were conducted to investigate the deformation and failure mechanisms under uniaxial shear and tension. Steered molecular dynamics simulations were carried out to study the interaction between different types of polymer chains. The results demonstrated that cellulose-hemicellulose and cellulose-lignin exhibit the strongest and weakest interactions, respectively. This conclusion was further validated against the DFT calculations. Additionally, through shear simulations of sandwiched polymer models, it was found that cellulose-hemicellulose-cellulose exhibits the highest strength and toughness, while cellulose-lignin-cellulose shows the lowest strength and toughness among all tested cases. This conclusion was further confirmed by uniaxial tension simulations of sandwiched polymer models. It was revealed that hydrogen bonds formed between the polymer chains are responsible for the observed strengthening and toughening behaviors. Additionally, it was interesting to note that failure mode under tension varies with the density of amorphous polymers located between cellulose bundles. The failure mode of multilayer polymer models under tension was also investigated. The findings of this work could potentially provide guidelines for the design of coconut-inspired lightweight cellular materials.

Capillary forces exerted by a water bridge on cellulose nanocrystals: the effect of an external electric field

Capillary forces play an important role during the dewatering and drying of nanocellulosic materials. Traditional moisture removal techniques, such as heating, have been proved to be deterimental to the properties of these materials and hence, there is a need to develop novel dewatering techniques without affecting the desired properties of materials. It is, therefore, important to explore novel methods for dewatering these high-added-value materials without negatively influencing their properties. In this context, we explore the effect of electric field on the capillary forces developed by a liquid-water bridge between two cellulosic surfaces, which may be formed during the water removal process following its displacement from the interfibrillar spaces. All-atom molecular dynamics (MD) simulations have been used to study the influence of an externally applied electric field on the capillary force exerted by a water bridge. Our results suggest that the equilibrium contact angle of water and the capillary force exerted by the water bridge between two nanocellulosic surfaces depend on the magnitude and direction of the externally applied electric fields. Hence, an external electric field can be applied to manipulate the capillary forces between two particles. The close agreement between the capillary forces measured through MD simulations and those calculated through classical equations indicates that, within the range of the electric field applied in this study, Young-Laplace equations can be safely employed to predict the capillary forces between two particles. The present study provides insights into the use of electric fields for drying of nanocellulosic materials.

Cellulose Nanocrystals: Tensile Strength and Failure Mechanisms Revealed Using Reactive Molecular Dynamics

Cellulose nanocrystals (CNCs) offer excellent mechanical properties. However, measuring the strength by performing reliable experiments at the nanoscale is challenging. In this paper, we model Iβ crystalline cellulose using reactive molecular dynamics simulations. Taking the fibril twist into account, structural changes and hydrogen-bonding characteristics of CNCs during the tensile test are inspected and the failure mechanism of CNCs is analyzed down to the scale of individual bonds. The C4-O4 glycosidic bond is found to be responsible for the failure of CNCs. Finally, the effect of strain rate on ultimate properties is analyzed and a nonlinear model is used to predict the ultimate strength of 9.2 GPa and ultimate strain of 8.5% at a 1 s^-1 strain rate. This study sheds light on the applications of cellulose in nanocomposites and further modeling of cellulose nanofibres.

Efficient Softening and Toughening Strategies of Cellulose Nanofibril Nanocomposites Using Comb Polyurethane

Cellulose nanofibrils (CNFs) have attracted attention as building blocks for sustainable materials owing to their high performance and the advantages of their abundant natural resources. Bioinspired CNF/polymer nanocomposites, consisting of a soft polymer phase and a high fraction (>50 wt %) of CNF reinforcement, have been focused on excellent mechanical properties, including Young's modulus, mechanical strength, and toughness, mimicking the energy dissipation system in nature. However, efficient softening and toughening with a small amount of the soft phase is still a challenge because a large amount of the polymer phase (nearly 50%) is still required to provide ductility and toughness. Here, we describe a topological strategy in the polymer phase for efficient toughening of bioinspired CNF nanocomposites with a water-soluble comb polyurethane (PU). The comb PU provided higher elongation at break and more efficient flexibility for the nanocomposite than the linear PU, even at a small content. Moreover, CNF nanocomposites with 30 wt % of PU content and tetrabutylammonium as bulky counterions showed enhanced toughness (180% higher) and strain at break (250% higher) when compared to pure CNF due to the promotion of slippage between nanofibrils. Scanning electron microscopy (SEM) images of the fracture surface for CNF/comb PU nanocomposites displayed the pull-out of mesoscale layers and nanofibrils, supporting that the comb topology promotes the slippage between fibrils. Furthermore, the rheological study revealed that the comb PU has an entanglement plateau modulus lower than linear PU by 1 order of magnitude, related to the loosened entanglements. Our study establishes an efficient softening and toughening strategy while using small amounts of polymer phase addition, promoting interfibrillar slippage with the loosely entangled comb PU phase.

Pyrolytic activation of cellulose: Energetics and condensed phase effects

Bottom-up design of lignocellulose pyrolysis to optimize the quality and yield of bio-oil is hindered by the limited knowledge of the underlying condensed phase biomass chemistry. The influence of condensed...

Combining Computational Chemistry and Crystallography for a Better Understanding of the Structure of Cellulose

The approaches in this article seek to enhance understanding of cellulose at the molecular level, independent of the source and the particular crystalline form of cellulose. Four main areas of structure research are reviewed. Initially, the molecular shape is inferred from the crystal structures of many small molecules that have β-(1→4) linkages. Then, conformational analyses with potential energy calculations of cellobiose are covered, followed by the use of Atoms-In-Molecules theory to learn about interactions in experimental and theoretical structures. The last section covers models of cellulose nanoparticles. Controversies addressed include the stability of twofold screw-axis conformations, the influence of different computational methods, the predictability of crystalline conformations by studies of isolated molecules, and the twisting of model cellulose crystals.

Morphology of Nanometric Overlayers Made of Porphyrin-Type Molecules Physisorbed on Cellulose Iβ Crystals and Nanocrystals

Molecular dynamics simulations based on an atomistic empirical force field have been carried out to investigate structural, thermodynamic, and dynamical properties of adlayers made of porphyrin-type molecules physisorbed on surfaces of cellulose Iβ nanocrystals. The results show that low-index surfaces provide a thermally stable, weakly perturbing support for the deposition of non-hydrogen-bonded organic molecules. At submonolayer coverage, the discoidal porphyrin molecules lay flat on the surface, forming compact 2D clusters with clear elements of ordering. The adlayer grows layer-by-layer for the smallest porphyrin species on compact cellulose surfaces, while forming 3D clusters on a first relatively ordered adlayer (Stranski-Krastanov growth) in all other cases. The adsorption energy exceeds ∼1 eV per molecule, underlying the thermal stability of the adsorbate. Entropy plays a non-negligible role, destabilizing to some extent the adlayer. The in-plane dynamics of the smallest porphyrin species, i.e., porphine, on compact surfaces shows signs of superlubricity, due to the low energy and momentum exchange between the flat admolecule and the equally flat cellulose surface.

Thermoconformational Behavior of Cellulose Nanofiber Films as a Device Substrate and Their Superior Flexibility and Durability to Glass

The design and high-throughput manufacturing of thin renewable energy devices with high structural and atomic configurational stability are crucial for the fabrication of green electronics. Yet, this concept is still in its infancy. In this work, we report the extraordinary durability of thin molecular interlayered organic flexible energy devices based on chemically tuned cellulose nanofiber transparent films that outperform glass by decreasing the substrate weight by 50%. The nanofabricated flexible thin film has an exceptionally low thermal coefficient of expansion of 1.8 ppm/K and a stable atomic configuration under a harsh fabrication condition (over 190 °C for an extended period of 5 h). A flexible optoelectronic device using the same renewable cellulose nanofiber film substrate was found to be functionally operational over a life span of 5 years under an intermittent operating condition. The success of this device's stability opens up an entirely new frontier of applications of flexible electronics.

Dynamical Water Ingress and Dissolution at the Amorphous-Crystalline Cellulose Interface

The use of cellulose has considerable promise in a wide range of industrial applications but is hampered by degradation in mechanical properties due to ambient moisture uptake. Existing models of equilibrium moisture content can predict the impact of these effects, but at present, the dynamical, atomic-scale picture of water ingress into cellulose is lacking. The present work reports nonequilibrium molecular simulations of the interface between cellulose and water aimed at capturing the initial stages of two simultaneous dynamical processes, water ingress into cellulose and cellulose dissolution into water. These simulations demonstrate that the process depends on the temperature and chain length in the amorphous region, where high temperatures can induce more mass exchange and short chains can easily detach from amorphous cellulose. A cooperative mechanism that involves both chemical and physical aspects, namely, hydrogen bonding and chain intertwining, respectively, is proposed to interpret the incipient dual ingress/dissolution process. Outcomes of this work will provide a foundation for cellulose functionalization strategies to impede moisture uptake and preserve the mechanical properties of nanocellulose in applications.

Understanding Plant Biomass via Computational Modeling

Plant biomass, especially wood, has been used for structural materials since ancient times. It is also showing great potential for new structural materials and it is the major feedstock for the emerging biorefineries for building a sustainable society. The plant cell wall is a hierarchical matrix of mainly cellulose, hemicellulose, and lignin. Herein, the structure, properties, and reactions of cellulose, lignin, and wood cell walls, studied using density functional theory (DFT) and molecular dynamics (MD), which are the widely used computational modeling approaches, are reviewed. Computational modeling, which has played a crucial role in understanding the structure and properties of plant biomass and its nanomaterials, may serve a leading role on developing new hierarchical materials from biomass in the future.

Aging Characteristics of Transformer Oil-Impregnated Insulation Paper Based on Trap Parameters

Oil-impregnated insulation paper is an important part of transformers; its performance seriously affects the life of power equipment. It is of significance to study the aging characteristics and mechanism of oil-impregnated insulation paper under thermal stress for transformer status detection and evaluation. In the work, the accelerated thermal aging was carried out at 120 °C, and DP1490, DP787, and DP311 samples were selected to represent the new, mid-aging, and late-aging status of the transformer, respectively. The space charge distribution within the specimens was measured by the pulsed electro-acoustic (PEA) method and the trap parameters were extracted based on the measurement curves. Further, the aging mechanism was studied by molecular simulation technology. A typical molecular chain defect model was constructed to study the motion of cellulose molecules under thermal stress. The experimental results show that the corresponding trap energy levels are 0.54 eV, 0.73 eV, and 0.92 eV for the new specimen, the mid-aging specimen, and the late aging specimen, respectively. The simulation results show that the trapped energy at the beginning of aging is mainly determined by the loss of H atoms. The changes in trap energy in the middle stage of aging are mainly caused by the absence of some C atoms, and the trap energy level at the end of aging is mainly caused by the breakage of chemical bonds. This study is of great significance to reveal the aging mechanism of oil-impregnated insulation paper and the modification of insulation paper.

Modification of pineapple leaf fibers with aminosilanes as adsorbents for H2S removal

Pineapple leaves were used as a natural fiber source to prepare various modified microcrystalline cellulose (MCC) samples as sorbents for H₂S sorption. Pineapple leaf fibers were first extracted from pineapple leaves, followed by hydrolyzing to produce MCC before various modifications using primary amine (3-aminopropyltrimethoxysilane, APS), secondary amine (N-methyl-3-aminopropyltrimethoxysilane, MAPS), or tertiary amine (N,N-dimethyl-3-aminopropyltrimethoxysilane, DAPS). The characterization results proved that all the aminosilane groups were successfully grafted onto the MCC. In addition, the thermal stability and the porosity of the modified sorbents were enhanced relative to those of unmodified MCC. The H₂S sorption studies of MCC modified with APS, MAPS, and DAPS at 0, 3, or 5%w/w showed that MCC-MAPS had better H₂S sorption performance than MCC-APS and MCC-DAPS, respectively, when comparing the H₂S sorption performance at the same loading level. The optimum H₂S sorption performance of each aminosilane group was achieved from MCC-APS at 5%, MCC-MAPS at 3%, and MCC-DAPS at 5%. An additional study of H₂S sorption of these three sorbents in the presence of CO₂ showed that MCC-DAPS at 5% was the best sorbent for selective H₂S removal. Our results indicated that MCC modified with the aminosilane groups, especially MAPS, were promising materials for H₂S sorption, with potential application in gas separation.

Wettability of cellulose surfaces under the influence of an external electric field

HYPOTHESIS

Interfacial tensions play an important role in dewatering of hydrophilic materials like nanofibrillated cellulose, and are affected by the molecular organization of water at the interface. Application of an electric field influences the orientation of water molecules along the field direction. Hence, it should be possible to alter the interfacial free energies to tune the wettability of cellulose surface through application of an external electric field thus, aiding the dewatering process.

SIMULATIONS

Molecular dynamics simulations of cellulose surface in contact with water under the influence of an external electric field have been conducted with GLYCAM-06 forcefield. The effect of variation in electric field intensity and directions on the spreading coefficient has been addressed via orientational preference of water molecules and interfacial free energy analyses.

FINDINGS

The application of electric field influences the interfacial free energy difference at the cellulose-water interface. The spreading coefficient increases with the electric field directed parallel to the cellulose-water interface while it decreases in the perpendicular electric field. Variation in interfacial free energies seems to explain the change in contact angle adequately in presence of an electric field. The wettability of cellulose surface can be tuned by the application of an external electric field.

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.

Tensile behaviour of dislocated/crystalline cellulose fibrils at the nano scale

Atomistic modelling of cellulose has widely been investigated for years using molecular dynamics simulations. In this paper, we model Iβ crystalline cellulose as well as develop a model including dislocations in between the crystal regions. The model including dislocations shows a tensile modulus of 109 GPa, 25% lower than that of the fully crystalline model (146 GPa). The change in dihedral angle preferences is analysed, and its effect on hydrogen bonding pattern is assessed. How presence of hydrogen bonds contributes to elastic properties of cellulose nano-fibrils is shown. Effect of water on the elastic modulus of fibrils is also investigated. Moreover, an illustration is given of how the tensile behaviour of fibrils is controlled by a synergy between the geometry changes occurring at the glycosidic linkage, reflected by specific torsional and glycosidic angles. These findings can be useful in further modelling of cellulosic fibrils at the atomistic and coarse-grained scales.

Steered Pull Simulation to Determine Nanomechanical Properties of Cellulose Nanofiber

Cellulose nanofiber (CNF) exhibits excellent mechanical properties, which has been extensively proven through experimental techniques. However, understanding the mechanisms and the inherent structural behavior of cellulose is important in its vastly growing research areas of applications. This study focuses on taking a look into what happens to the atomic molecular interactions of CNF, mainly hydrogen bond, in the presence of external force. This paper investigates the hydrogen bond disparity within CNF structure. To achieve this, molecular dynamics simulations of cellulose Iβ nanofibers are carried out in equilibrated conditions in water using GROMACS software in conjunction with OPLS-AA force field. It is noted that the hydrogen bonds within the CNF are disrupted when a pulling force is applied. The simulated Young’s modulus of CNF is found to be 161 GPa. A simulated shear within the cellulose chains presents a trend with more hydrogen bond disruptions at higher forces.

Interfacial Adhesion of Polylactic Acid on Cellulose Surface: A Molecular Dynamics Study

Interfacial bonding and adhesion mechanisms are important in determining the final properties of the polymer composite. Molecular dynamics (MD) simulations have been used to characterize the interfacial structure and adhesion behavior of crystalline cellulose planes in contact with polylactic acid. The structure of the PLA at the interface exhibits a shape that can accommodate the structure of the cellulose surface. The adhesion between the PLA and the cellulose surface is affected by the polarity of the functional groups and the surface roughness. The improved adhesion is primarily due to hydrogen bonds formed between the cellulose and PLA molecular chains. Cellulose planes with higher molecular protrusions and greater surface roughness produce stronger adhesion to PLA due to enhanced hydrogen bonding. This study provides a basic insight into the interfacial mechanisms of PLA and cellulose surfaces at the molecular level.

Discovery and design of soft polymeric bio-inspired materials with multiscale simulations and artificial intelligence

Establishing the “Materials 4.0” paradigm requires intimate knowledge of the virtual space in materials design.

Thermal Response in Cellulose Iβ Based on Molecular Dynamics

The structural details of cellulose I β were discussed according to molecular dynamics simulations with the GLYCAM-06 force field. The simulation outcomes were in agreement with previous experimental data, including structural parameters and hydrogen bond pattern at 298 K. We found a new conformation of cellulose Iβ existed at the intermediate temperature that is between the low and high temperatures. Partial chain rotations along the backbone direction were found and conformations of hydroxymethyl groups that alternated from tg to either gt or gg were observed when the temperature increased from 298 K to 400 K. In addition, the gg conformation is preferred than gt. For the structure adopted at high temperature of 500 K, major chains were twisted and two chains detached from each plain. In contrast to the observation under intermediate temperature, the population of hydroxymethyl groups in gt exceeded that in gg conformation at high temperature. In addition, three patterns of hydrogen bonding were identified at low, intermediate and high temperatures in the simulations. The provided structural information indicated the transitions occurred around 350 K and 450 K, considered as the transitional temperatures of cellulose Iβ in this work.

Wood–Moisture Relationships Studied with Molecular Simulations: Methodological Guidelines

This paper aims at providing a methodological framework for investigating wood polymers using atomistic modeling, namely, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Atomistic simulations are used to mimic water adsorption and desorption in amorphous polymers, make observations on swelling, mechanical softening, and on hysteresis. This hygromechanical behavior, as observed in particular from the breaking and reforming of hydrogen bonds, is related to the behavior of more complex polymeric composites. Wood is a hierarchical material, where the origin of wood-moisture relationships lies at the nanoporous material scale. As water molecules are adsorbed into the hydrophilic matrix in the cell walls, the induced fluid–solid interaction forces result in swelling of these cell walls. The interaction of the composite polymeric material, that is the layer S2 of the wood cell wall, with water is known to rearrange its internal material structure, which makes it moisture sensitive, influencing its physical properties. In-depth studies of the coupled effects of water sorption on hygric and mechanical properties of different polymeric components can be performed with atomistic modeling. The paper covers the main components of knowledge and good practice for such simulations.

Molecular insight into the wetting behavior and amphiphilic character of cellulose nanocrystals

The study of nanocellulose is a field of growing interest due to its many applications and its use in the development of biocompatible and eco-friendly materials. In spite of the vast number of studies in the field, many questions about the role of the molecular structure in the properties of cellulose are still subject of debate. One of these fundamental questions is the possible amphiphilic nature of cellulose and the relative role of hydrogen bonding and hydrophobic effect on the interactions of cellulose. In this work we present an extensive molecular dynamics simulation study of this question by analyzing the wetting of cellulose with water and organic solvent, its interaction with hydrophilic and hydrophobic ions and its interaction with a protein (human epidermal growth factor, hEGF). We consider two characteristic cellulose crystal planes of Iβ cellulose with very different roughness, different hydrogen bonding capability and different exposure of cellulose hydrophobic groups (the (010) plane which has exposed -OH groups and the (100) plane with buried -OH groups). Our results show that both surfaces are simultaneously hydrophilic and lipophilic, with both surfaces having very similar contact angles. In spite of the global similarity of wetting of both surfaces, the molecular details of wetting are very different and substantial local wetting heterogeneities (which strongly depend on the surface) appear for both solvents. We also observe a weak interaction of both surfaces with hydrophobic and hydrophilic solutes. These weak interactions are attributed to the simultaneous lipophilic and hydrophilic character of both (100) and (010) cellulose surfaces. Interestingly, we found a substantial interaction of both cellulose planes with polar and apolar residues of the hEGF protein.

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.

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.

Extraction and modification of cellulose nanofibers derived from biomass for environmental application

Cellulose nanofibers obtained from various plants and microbial sources, their extraction methods and various environmental applications are discussed.

On the origins of the elasticity of cellulose nanofiber nanocomposites and nanopapers: a micromechanical approach

The elastic properties of cellulose nanofibril (NFC) nanocomposites and nanopapers are predicted by a multiscale network model that shows that the deformation mechanisms are governed by the bonds between rigid NFC segments and in the kinked regions.

Molecular deformation mechanisms in cellulose allomorphs and the role of hydrogen bonds

Differences in tensile properties between cellulose crystal allomorphs cannot be rationalized by simply counting hydrogen bonds. From molecular dynamics computer simulations the cooperative nature of energy contributions to axial cellulose crystal modulus becomes apparent. Using a decomposition of inter and intramolecular forces as a function of tensile strain, the three allomorphs show dramatic differences in terms of how the contributions to elastic energy are distributed between covalent bonds, angles, dihedrals, electrostatic forces, dispersion and steric forces.

Unique aspects of the structure and dynamics of elementary Iβ cellulose microfibrils revealed by computational simulations

The question of how many chains an elementary cellulose microfibril contains is critical to understanding the molecular mechanism(s) of cellulose biosynthesis and regulation. Given the hexagonal nature of the cellulose synthase rosette, it is assumed that the number of chains must be a multiple of six. We present molecular dynamics simulations on three different models of Iβ cellulose microfibrils, 18, 24, and 36 chains, to investigate their structure and dynamics in a hydrated environment. The 36-chain model stays in a conformational space that is very similar to the initial crystalline phase, while the 18- and 24-chain models sample a conformational space different from the crystalline structure yet similar to conformations observed in recent high-temperature molecular dynamics simulations. Major differences in the conformations sampled between the different models result from changes to the tilt of chains in different layers, specifically a second stage of tilt, increased rotation about the O2-C2 dihedral, and a greater sampling of non-TG exocyclic conformations, particularly the GG conformation in center layers and GT conformation in solvent-exposed exocyclic groups. With a reinterpretation of nuclear magnetic resonance data, specifically for contributions made to the C6 peak, data from the simulations suggest that the 18- and 24-chain structures are more viable models for an elementary cellulose microfibril, which also correlates with recent scattering and diffraction experimental data. These data inform biochemical and molecular studies that must explain how a six-particle cellulose synthase complex rosette synthesizes microfibrils likely comprised of either 18 or 24 chains.

Solution Properties of Hemicellulose Polysaccharides with Four Common Carbohydrate Force Fields

Hemicellulose polysaccharides play an important role in the swelling behavior of the primary plant cell wall, and molecular dynamics simulations provide the means of gaining a concise understanding of the interactions of hemicellulose polysaccharides with water. Here, we compare four of the main polysaccharide force fields (CHARMM36 TIP3P, GROMOS56A6(CARBO) SPC, GLYCAM06h TIP3P, and GLYCAM06h TIP5P) for the most abundant hemicellulose backbone components. In particular, we compare aggregation, diffusion coefficients, system density, and investigate the free energy of hydration of saccharides in water. We find that the saccharides show nonphysical aggregation at low concentrations with the GLYCAM06h TIP3P force field, which can be rectified by the use of the TIP5P water model. As a result of the aggregation, GLYCAM06h TIP3P does not lead to reasonable diffusion coefficients whereas the diffusion coefficients, as well as the system density, agrees best with experimental data for the GLYCAM06h TIP5P force field. Overall, GLYCAM06h TIP5P gives good agreement with experimental free energy of hydration data for small saccharides. In addition, the free energy of hydration for short polysaccharides calculated with the GLYCAM06h TIP5P force field is consistent with the radial distribution functions between the polysaccharides and water, the hydration number of the polysaccharides, and the hydrogen bonds formed in the system.