Water Adsorption in Wood Microfibril-Hemicellulose System: Role of the Crystalline–Amorphous Interface

Exploring xylan removal via enzymatic post-treatment to tailor the properties of cellulose nanofibrils for packaging film applications

Hemicellulose plays a key role in both the production of cellulose nanofibrils (CNF) and their properties as suspensions and films. While the use of enzymatic and chemical pre-treatments for tailoring hemicellulose levels is well-established, post-treatment methods using enzymes remain relatively underexplored and hold significant promise for modifying CNF film properties. This study aimed to investigate the effects of enzymatic xylan removal on the properties of CNF film for packaging applications. The enzymatic post-treatment was carried out using an enzymatic cocktail enriched with endoxylanase (EX). The EX post-treated-CNFs were characterized by LALLS, XRD, and FEG-SEM, while their films were characterized in terms of physical, morphological, optical, thermal, mechanical, and barrier properties. Employing varying levels of EX facilitated the hydrolysis of 8 to 35 % of xylan, yielding CNFs with different xylan contents. Xylan was found to be vital for the stability of CNF suspensions, as its removal led to the agglomeration of nanofibrils. Nanostructures with preserved crystalline structures and different morphologies, including nanofibers, nanorods, and their hybrids were observed. The EX post-treatment contributed to a smoother film surface, improved thermostability, and better moisture barrier properties. However, as the xylan content decreased, the films became lighter (lower grammage), less strong, and more brittle. Thus, the enzymatic removal of xylan enabled the customization of CNF films' performance without affecting the inherent crystalline structure, resulting in materials with diverse functionalities that could be explored for use in packaging films.

Advanced Molecular Dynamics Model for Investigating Biological-Origin Microfibril Structures

Understanding the atomic-scale structure of wood microfibrils is essential for establishing fundamental properties in various wood-based research aspects, including moisture impact, wood modification, and pretreatment. In this study, we employed molecular dynamics simulations to investigate the arrangement of wood polymers, including cellulose, hemicellulose, and lignin, with a primary focus on the composition of softwood, specifically Norway Spruce wood. We assessed the accuracy of our molecular dynamics model by comparing it with available experimental data, such as density, Young's modulus, and glass transition temperature, which ensures the reliability of our approach. A key aspect of our study involved modeling the active sorption site for water interaction with wood polymers. Our findings revealed that the interaction between water and hemicellulose, particularly within the hemicellulose-cellulose interphase, was the most prominent binding site. This observation aligns with prior research in this field, further strengthening the validity of our results.

Structural and mechanical roles of wood polymer assemblies in softwood revealed by gradual removal of polysaccharides or lignin

A deep understanding of the inherent roles of wood polymers such as cellulose, hemicelluloses, and lignin in the hierarchical structure of wood is of key importance for advancing functional wood-based materials but is currently lacking. To address this gap, we clarified the underexplored contributions of wood polymer assemblies to the structural support and compressive properties of wood by chemically removing polysaccharides or lignin from wood blocks of a conifer Cryptomeria japonica. Compositional and structural evaluations revealed that cellulose, hemicelluloses, and lignin contributed to the dimensional stability of wood, especially that the polysaccharide network at cell corners sustained the honeycomb cell structure. Wood polymer assemblies featuring the anatomical structure of wood were also evaluated in terms of compressive properties. The modulus and strength reflected the density and anisotropy, whereas fracture behavior was well characterized by each wood polymer assembly through the classification of stress-strain curves based on principal component analysis. The difference in fracture behaviors indicated that the rigid lignin and flexible cellulose assemblies, possibly mediated by hemicelluloses, complementarily determine the unique compressive response of wood. These findings enable the adjustment of wood functionality and the selection of composite components for wood modification while inspiring the development of novel wood applications.

Unveiling moisture transport mechanisms in cellulosic materials: Vapor vs. bound water

Natural textiles, hair, paper, wool, or bio-based walls possess the remarkable ability to store humidity from sweat or the environment through "bound water" absorption within nanopores, constituting up to 30% of their dry mass. The knowledge of the induced water transfers is pivotal for advancing industrial processes and sustainable practices in various fields such as wood drying, paper production and use, moisture transfers in clothes or hair, humidity regulation of bio-based construction materials, etc. However, the transport and storage mechanisms of this moisture remain poorly understood, with modeling often relying on an assumption of dominant vapor transport with an unknown diffusion coefficient. Our research addresses this knowledge gap, demonstrating the pivotal role of bound water transport within interconnected fiber networks. Notably, at low porosity, bound water diffusion dominates over vapor diffusion. By isolating diffusion processes and deriving diffusion coefficients through rigorous experimentation, we establish a comprehensive model for moisture transfer. Strikingly, our model accurately predicts the evolution of bound water's spatial distribution for a wide range of sample porosities, as verified through magnetic resonance imaging. Showing that bound water transport can be dominant over vapor transport, this work offers a change of paradigm and unprecedented control over humidity-related processes.

Critical Role of Boundary Conditions in Sorption Kinetics Measurements

In order to characterize the hygroscopic properties of cellulose-based materials, which can absorb large amounts of water from vapor in ambient air, or the adsorption capacity of pollutants or molecules in various porous materials, it is common to rely on sorption-desorption dynamic tests. This consists of observing the mass variation over time when the sample is placed in contact with a fluid containing the elements to be absorbed or adsorbed. Here, we focus on the case of a hygroscopic material in contact with air at a relative humidity (RH) differing from that at which it has been prepared. We show that the vapor mass flux going out of the sample follows from the solution of a vapor convection-diffusion problem along the surface and is proportional to the difference between the RH of the air flux and that along the surface with a multiplicative factor (δ) depending only on the characteristics of the air flux and the geometry of the system, including the surface roughness. This factor may be determined from independent measurements in which the RH along the surface is known while keeping all other variables constant. Then we show that the apparent sorption or desorption kinetics critically depend on the competition between boundary conditions and transport through the material. For sufficiently low air flux intensities or small sample thicknesses, the moisture distribution in the sample remains uniform and evolves toward the equilibrium with a kinetics depending on the value of δ and the material thickness. For sufficiently high air flux intensities or large sample thicknesses, the moisture distribution is highly inhomogeneous, and the kinetics reflect the ability of water transport by diffusion through the material. We illustrate and validate this theoretical description on the basis of magnetic resonance imaging experiments on drying cellulose fiber stacks.

Water Adsorption on Hydrophilic Fibers and Porous and Deliquescent Materials: Cellulose, Polysaccharide, Silica, Inorganic Salt, Sugar Alcohol, and Amino Acid

Water adsorption isotherms are systematically summarized by using celluloses and polysaccharides as hydrophilic crystal/amorphous materials with functional groups, silicas as hydrophilic porous materials, and inorganic salts, sugar alcohols, and amino acids as hygroscopic deliquescent materials. For hydrophilic fibers such as celluloses and polysaccharides, water was adsorbed on amorphous solids, and water clusters were formed around functional groups. For porous materials such as silicas, capillary condensation occurred in the micropores of silicas. For deliquescent materials such as inorganic salts, sugar alcohols, and amino acids, water adsorption rapidly increased stepwise at a specific threshold relative humidity, accompanied with a structure transformation to a liquid state. In addition, the water activity (Aw) of materials used in packed products was able to be estimated from the water adsorption isotherms of the pure component. This indicated that the deliquescent materials have a great effect on the depression of Aw for the suppression of microbial growth at an extremely high water content. The deliquescent materials could be useful to develop new environmentally and sustainable products and technologies with the mediation of water vapor and/or hydration.

Cellulose: A Review of Water Interactions, Applications in Composites, and Water Treatment

Cellulose is known to interact well with water, but is insoluble in it. Many polysaccharides such as cellulose are known to have significant hydrogen bond networks joining the molecular chains, and yet they are recalcitrant to aqueous solvents. This review charts the interaction of cellulose with water but with emphasis on the formation of both natural and synthetic fiber composites. Covering studies concerning the interaction of water with wood, the biosynthesis of cellulose in the cell wall, to its dispersion in aqueous suspensions and ultimately in water filtration and fiber-based composite materials this review explores water-cellulose interactions and how they can be exploited for synthetic and natural composites. The suggestion that cellulose is amphiphilic is critically reviewed, with relevance to its processing. Building on this, progress made in using various charged and modified forms of nanocellulose to stabilize oil-water emulsions is addressed. The role of water in the aqueous formation of chiral nematic liquid crystals, and subsequently when dried into composite films is covered. The review will also address the use of cellulose as an aid to water filtration as one area where interactions can be used effectively to prosper human life.

Fiber Templated Epitaxially Grown Composite Membranes: From Thermal Insulation to Infrared Stealth

Thermal insulation materials show a substantial impact on civil and military fields for applications. Fabrication of efficient, flexible, and comfortable composite materials for thermal insulation is thereby of significance. Herein, a "fiber templated epitaxial growth" strategy was adopted to construct PAN@LDH (PAN = polyacrylonitrile; LDH = layered double hydroxides) composite membranes with a three-dimensional (3D) network structure. The PAN@LDH showed an impressive temperature difference of 28.1 °C as a thermal insulation material in the hot stage of 80 °C with a thin layer of 0.6 mm. Moreover, when a human hand was covered with 3 layers of the PAN@LDH-70% composite membrane, it was rendered invisible under infrared radiation. Such excellent performance can be attributed to the following reasons: (1) the hierarchical interfaces of the PAN@LDH composite membrane reduced thermal conduction, (2) the 3D network structure of the PAN@LDH composite membranes restricted thermal convection, and (3) the selective infrared absorption of LDHs decreased thermal radiation. When modified with Dodecyltrimethoxysilane (DTMS), the resulting PAN@LDH@DTMS membrane can be used under high humidity conditions with excellent thermal insulation properties. As such, this work provides a facile strategy for the development of high-performance thermal insulation functional membranes.

Deconstruction and Reassembly of Renewable Polymers and Biocolloids into Next Generation Structured Materials

This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.

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.

Thermally Insulating Nanocellulose-Based Materials

Thermally insulating materials based on renewable nanomaterials such as nanocellulose could reduce the energy consumption and the environmental impact of the building sector. Recent reports of superinsulating cellulose nanomaterial (CNM)-based aerogels and foams with significantly better heat transport properties than the commercially dominating materials, such as expanded polystyrene, polyurethane foams, and glass wool, have resulted in a rapidly increasing research activity. Herein, the fundamental basis of thermal conductivity of porous materials is described, and the anisotropic heat transfer properties of CNMs and films with aligned CNMs and the processing and structure of novel CNM-based aerogels and foams with low thermal conductivities are presented and discussed. The extraordinarily low thermal conductivity of anisotropic porous architectures and multicomponent approaches are highlighted and related to the contributions of the Knudsen effect and phonon scattering.

Cellulose-hemicellulose interactions - A nanoscale view

In this work, we study interactions of five different hemicellulose models, i.e. Galactoglucomannan, O-Acetyl-Galactoglucomannan, Fuco-Galacto-Xyloglucan, 4-O-Methylglucuronoxylan, and 4-O-Methylglucuronoarabinoxylan, and their respective binding strength to cellulose nanocrystals by molecular dynamics simulations. Glucuronoarabinoxylan showed the highest free energy of binding, whereas Xyloglucan had the lowest interaction energies amongst the five models. We further performed simulated shear tests and concluded that failure mostly happens at the inter-molecular interaction level within the hemicellulose fraction, rather than at the interface with cellulose. The presence of water molecules seems to have a weakening effect on the interactions of hemicellulose and cellulose, taking up the available hydroxyl groups on the surface of the cellulose for hydrogen bonding. We believe that these studies can shed light on better understanding of plant cell walls, as well as providing evidence on variability of the structures of different plant sources for extractions, purification, and operation of biorefineries.

Wood Modification as a Tool to Understand Moisture in Wood

Moisture plays a central role in the performance of wood products because it affects important material properties such as the resistance to decomposition, the mechanical properties, and the dimensions. To improve wood performance, a wide range of wood modification techniques that alter the wood chemistry in various ways have been described in the literature. Typically, these modifications aim to improve resistance to decomposition, dimensional stability, or, to introduce novel functionalities in the wood. However, wood modification techniques can also be an important tool to improve our understanding of the interactions between wood and moisture. In this review, we describe current knowledge gaps in our understanding of moisture in wood and how modification has been and could be used to clarify some of these gaps. This review shows that introducing specific chemical changes, and even controlling the distribution of these, in combination with the variety of experimental methods available for characterization of moisture in wood, could give novel insights into the interaction between moisture and wood. Such insights could further contribute to applications in several related fields of research such as how to enhance the resistance to decomposition, how to improve the performance of moisture-induced wooden actuators, or how to improve the utilization of wood biomass with challenging swelling anisotropy.

Wood Fuel Procurement to Bioenergy Facilities: Analysis of Moisture Content Variability and Optimal Sampling Strategy

Moisture content is the most relevant quality parameter for wood fuels. Effective and fast determination of moisture of incoming feedstock is essential in the management of bioenergy facilities. The availability of fast and reliable moisture meters based on innovative technologies simplifies this task. However, in Mediterranean conditions the inherent variability of wood fuels calls for a careful sampling strategy if representative results are required while facing acceptable analytic costs. The present study is aimed at measuring the fuel heterogeneity and defining accordingly the appropriate number of samples to be analyzed in order to get reliable moisture-content results. A total of 70 truckloads (about 2270 t of woodchips) were sampled during commercial operations in two different seasons. Five samples were collected from each load and measured with standard method and magnetic resonance gauge. Results show that the variability of moisture content is influenced by mixing of species and storage of biomass. Heterogeneity can vary greatly also within single truckloads, to the point that three samples are needed to achieve about 90% of estimates within the desired precision limits. In the case of larger lots, such as barge or ship loads, 20 samples can provide sufficient precision in most scenarios.

Micro- and nanofibrillated cellulose from virgin and recycled fibers: A comparative study of its effects on the properties of hygiene tissue paper

This study aims to understand the effect of micro- and nanofibrillated cellulose (MNFC) on the tensile index, softness, and water absorbency of tissue paper. MNFC was produced from four different fiber sources. The results show that MNFC acts as an effective strength enhancer at the expense of a reduced water absorbency and softness. The impact of the fiber source on MNFC manufacturing cost and the trade-off with performance was also investigated. MNFCs produced from southern bleached hardwood kraft, northern bleached softwood kraft, and deinked pulp exhibited similar performance trends with the MNFC from the deinked pulp having a significantly lower cost. This suggests that MNFCs with similar degrees of fibrillation may be used interchangeably regardless of the fiber source, revealing the possibility to minimize MNFC manufacturing costs based on fiber selection. MNFC produced from bleached Eucalyptus kraft showed the lowest degree of fibrillation and the lowest strength improvements among the MNFCs evaluated.

Combining scattering analysis and atomistic simulation of wood-water interactions

Molecular-scale interactions between water and cellulose microfibril bundles in plant cell walls are not fully understood, despite their crucial role for many applications of plant biomass. Recent advances in X-ray and neutron scattering analysis allow more accurate interpretation of experimental data from wood cell walls. At the same time, microfibril bundles including hemicelluloses and water can be modelled at atomistic resolution. Computing scattering patterns from atomistic models enables a new, complementary approach to decipher some of the most fundamental questions at this level of the hierarchical cell wall structure. This article introduces studies related to moisture behavior of wood with small/wide-angle X-ray/neutron scattering and atomistic simulations, recent attempts to combine these two approaches, and perspectives and open questions for future research using this powerful combination. Finally, we discuss the opportunities of the combined method in relation to applications of lignocellulosic materials.

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.

Effects of Moisture on Diffusion in Unmodified Wood Cell Walls: A Phenomenological Polymer Science Approach

Despite the importance of cell wall diffusion to nearly all aspects of wood utilization, diffusion mechanisms and the detailed effects of moisture remain poorly understood. In this perspective, we introduce and employ approaches established in polymer science to develop a phenomenological framework for understanding the effects of moisture on diffusion in unmodified wood cell walls. The premise for applying this polymer-science-based approach to wood is that wood polymers (cellulose, hemicelluloses, and lignin) behave like typical solid polymers. Therefore, the movement of chemicals through wood cell walls is a diffusion process through a solid polymer, which is in contrast to previous assertions that transport of some chemicals occurs via aqueous pathways in the cell wall layers. Diffusion in polymers depends on the interrelations between free volume in the polymer matrix, molecular motions of the polymer, diffusant dimensions, and solubility of the diffusant in the polymer matrix. Because diffusion strongly depends on whether a polymer is in a rigid glassy state or soft rubbery state, it is important to understand glass transitions in the amorphous wood polymers. Through a review and analysis of available literature, we conclude that in wood both lignin and the amorphous polysaccharides very likely have glass transitions. After developing and presenting this polymer-science-based perspective of diffusion through unmodified wood cell walls, suggested directions for future research are discussed. A key consideration is that a large difference between diffusion through wood polymers and typical polymers is the high swelling pressures that can develop in unmodified wood cell walls. This pressure likely arises from the hierarchical structure of wood and should be taken into consideration in the development of predictive models for diffusion in unmodified wood cell walls.

Wood Moisture-Induced Swelling at the Cellular Scale—Ab Intra

Wood, a complex hierarchical material, continues to be widely used as a resource to meet humankind’s material needs, in addition to providing inspiration for the development of new biomimetic materials. However, for wood to meet its full potential, researchers must overcome the challenge of understanding its fundamental moisture-related properties across its many levels of hierarchy spanning from the molecular scale up to the bulk wood level. In this perspective, a review of recent research on wood moisture-induced swelling and shrinking is presented from the molecular level to the cellular scale. Numerous aspects of swelling and shrinking in wood remain poorly understood, sub-cellular phenomena in particular, because it can be difficult to study them experimentally. Here, we discuss recent research endeavors at each of the relevant length scales, including the molecular, cellulose elementary fibril, secondary cell wall layer nanostructure, cell wall, cell, and cellular levels. At each length scale, we provide a discussion on the current knowledge and suggestions for future research. The potential impacts of moisture-induced swelling pressures on experimental observations of swelling and shrinking in wood at different length scales are also recognized and discussed.

Mesoporosity of Delignified Wood Investigated by Water Vapor Sorption

Wood represents a highly suitable biobased scaffold for the development of mechanically robust and functional materials. Its functionalizability can be enhanced by means of delignification, resulting in an increase in porosity due to partial or complete removal of lignin and hemicellulose constituents. In this work, the impact of partial and complete delignification on the mesoporous structure is investigated via water vapor sorption isotherms and deuterium exchange. Pore size distributions of wood samples with five different delignification levels were compared to native wood. The derived pore size distributions at the water swollen state reveal an increase in porosity with decreasing lignin content. However, after complete lignin removal, drying causes a nonreversible collapse of the cell wall, which results in reduced porosity.

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.

Orthotropic Tension Behavior of Two Typical Chinese Plantation Woods at Wide Relative Humidity Range

Research Highlights: Orthotropic tension behaviors of poplar and Chinese fir were investigated at a wide relative humidity (RH) range. Background and Objectives: Poplar and Chinese fir are typical plantation tree species in China. Mechanical properties of plantation-grown wood varies from naturally-grown one. To utilize poplar and Chinese fir woods efficiently, fully understanding their moisture content (MC) and orthotropic dependency on tension abilities is necessary. Materials and Methods: Plantation poplar and Chinese fir wood specimens were prepared and conditioned in series RH levels (0–100%). Tensile modulus (E) and strength (σ) were tested in longitudinal (L), radial (R), and tangential (T) directions. Results: The E and σ results in transverse directions confirmed the general influence of the MC that decreased with increasing MC. However, both E and σ in L direction showed a trend that increased at first, and then decreased when MC increased. The local maximums of stiffness and strength may be associated with straightened non-crystalline cellulose, induced by the penetration of water into the wood cell wall. Using the visualization method for compliance, the tension abilities of poplar and Chinese fir exhibited clear moisture and orthotropic dependency. Conclusion: Both poplar and Chinese fir showed a significantly higher degree of anisotropy in the L, R, and T directions. The results in this study provided first-hand data for wooden construction and wood drying.

Cytotoxicity, bactericidal and hemostatic evaluation of oxidized cellulose microparticles: Structure and oxidation degree approach

Oxidized cellulose is the most used hemostatic materials in clinical applications. In addition to its perfect hemostatic efficiency, it is degradable under in vivo conditions and supremely prevents bacterial growth. On the other hand, one of the drawbacks of the oxidized cellulose is cytotoxicity due to the strongly acidic nature during degradation. There is a number of commercially available oxidized cellulose products which are derived from regenerated and non-regenerated cellulose. On the other hand, the effect of oxidation degree and structure (regenerated or non-regenerated) on product efficiency is undetermined. Moreover, oxidation degree which is primary factor for both bactericidal and hemostatic efficiency is also crucial for assessment of the product. In this study, oxidized cellulose versus oxidized regenerated cellulose microparticles with various oxidation degree was produced and characterized. Comparative studies were conducted in terms of bactericidal and hemostatic efficiencies in addition to cytotoxicity. The results could be a reference for the optimized oxidized cellulose product for the hemostatic applications.

Relationship between processing history and functionality recovery after rehydration of dried cellulose-based suspensions: A critical review

Cellulose-based suspensions have raised more and more attention due to their broad range of properties that can be used in paper industry and material science but also in medicine, nanotechnology and food science. Their final functionality is largely dependent on their processing history and notably the structural modifications that occur during drying and rehydration. The purpose of this work is to make a state-of-the-art contribution to the mechanisms involved in the process-structure-function relationships of cellulose-based hydrogels. The different assumptions that exist in the literature are reviewed taking the key role of the initial sample characteristics as well as the processing conditions into consideration. The decrease in swelling ability after drying is clearly due to an overall shrinkage of the structure of the material. At microscale, pore closure and cellulosic fibril aggregation are mentioned as the main reasons. The origins of such irreversible structural modifications take place at molecular level and is mainly explained by the establishment of a new balance of interactions between all components. Nevertheless, the respective contribution of each interaction are still under investigation.

Free Energy Landscape of Cellulose as a Driving Factor in the Mobility of Adsorbed Water

The diffusion coefficient of water adsorbed in hydrophilic porous materials, such as noncrystalline cellulose, depends on water activity. Faster diffusion at higher water concentrations is observed in experimental and modeling studies. In this paper, two asymptotic water concentrations, near-vacuum and fully saturated, are investigated at the surface of crystalline cellulose with molecular dynamics simulations. An increasing water concentration leads to significant changes in the free energy landscape due to perturbation of local electrostatic potential. Smoothening of strong energy minima, corresponding to sorption sites, and formation of layered structure facilitates water transport in the vicinity of cellulose. The determined transition probabilities and hydrogen bond stability reflect the changes in the energy landscape. As a result of a concentration increase, the emerging basins of attraction and spreading out of those existing in the diluted state lead to an increase in water entropy. Thermal fluctuations of cellulose are demonstrated to rearrange the landscape in the diluted limit, increase adsorbed water entropy, and decrease the water-cellulose H-bond lifetime.

Variation of Nanostructures, Molecular Interactions, and Anisotropic Elastic Moduli of Lignocellulosic Cell Walls with Moisture

A combination of experimental, theoretical and numerical studies is used to investigate the variation of elastic moduli of lignocellulosic (bamboo) fiber cell walls with moisture content (MC). Our Nanoindentation results show that the longitudinal elastic modulus initially increased to a maximum value at about 3% MC and then decreased linearly with increasing MC. In contrast, the transverse moduli decrease linearly with MC. We showed that amorphous materials in cell walls have key roles in the variation of elastic modulus with increasing MC. Elastic modulus of lignin, calculated by molecular dynamics simulations, increases initially with increasing MC, and then decreases. In contrast, elastic modulus of hemicellulose decreases constantly with MC. Below 10% MC, water molecules tend to break hydrogen bonds between polymer chains and form new hydrogen bond bridges between the polymer chains, while above 10% MC, water molecules aggregate together and create nano-droplets inside the materials. During the process of bridging, the fractional free volume of lignin decreases. The free volume reduction along with formation of hydrogen bond bridges causes a growth in elastic modulus of lignin at low MC. The constant increase of hemicellulose free volume, however, causes the aggregation of voids in the system and diminution of elastic properties.

Filler functionality in edible solid foams

We review the functionality of particulate ingredients in edible brittle foams, such as expanded starchy snacks. In food science and industry there is not a complete awareness of the full functionality of these filler ingredients, which can be fibers, proteins, starch granules and whole grains. But, we show that much can be learned about that from the field of synthetic polymeric foams with (nano)fillers. For edible brittle foams the enhancement of mechanical strength by filler ingredients is less relevant compared to the additional functionalities such as 1) the promotion of bubble nucleation and 2) cell opening-which are much more relevant for the snack texture. The survey of particulate ingredients added to snack formulations shows that they cannot be viewed as inert fillers, because of their strong hygroscopic properties. Hence, these fillers will compete with starch for water, and that will modify the glass transition and boiling point, which are important factors for snack expansion. Filler properties can be modified via extrusion, but it is better if that processing step is decoupled from the subsequent processing steps as mixing and expansion. Several filler ingredients are also added because of their nutritional value, but can have adverse effect on snack expansion. These adverse effects can be reduced if the increase of nutritional value is decoupled from other filler functionality via compartmentalization using micropellets.

Mimicking the Humidity Response of the Plant Cell Wall by Using Two-Dimensional Systems: The Critical Role of Amorphous and Crystalline Polysaccharides

Of the composite materials occurring in nature, the plant cell wall is among the most intricate, consisting of a complex arrangement of semicrystalline cellulose microfibrils in a dissipative matrix of lignin and hemicelluloses. Here, a biomimetic, two-dimensional cellulose system of the cell wall structure is introduced where cellulose nanocrystals compose the crystalline portion and regenerated amorphous cellulose composes the dissipative matrix. Spectroscopic ellipsometry and QCM-D are used to study the water vapor uptake of several two-layer systems. Quantitative analysis shows that the vapor-induced swelling of these ultrathin films can be controlled by varying ratios of the chemically identical ordered and unordered cellulose components. Intriguingly, increasing the share of crystalline cellulose appeared to increase the vapor uptake but only in cases for which the interfacial area between the crystalline and amorphous area was relatively large and the thickness of an amorphous overlayer was relatively small. The results show that a biomimetic approach may occasionally provide answers as to why certain native structures exist.