Water as an Intrinsic Structural Element in Cellulose Fibril Aggregates

Unveiling Synergistic Interface Effects on Charge Trapping Regulation in Polymer Composite Dielectrics through Multiscale Modeling

Interface design is a promising strategy to enhance the dielectric strength in polymer composites through regulating the charge transport process. However, the targeted exploitation of interface effects is limited due to a lack of fundamental understanding of the underlying mechanisms involving elementary electronic processes and details of the intricate interplay of characteristics of molecular building blocks and the interfacial morphology - details that cannot fully be resolved with experimental methods or commonly used band transport models. Here, we instead build a proper theoretical framework for polymer dielectrics based on charge hopping and employ a multiscale modeling approach linking the quantum properties of the charge carriers with nano- and mesoscale structural details of complex interfaces. Applied to a prototypical application-proven cellulose-oil interface system, this approach demonstrates that charges are trapped in the disordered region. Specifically, it unveils this trapping as a synergistic effect of two transport-regulating interface mechanisms: back-transfer to the oil region is suppressed by energetic factors, while forward-transfer to the crystalline cellulose is suppressed by low electronic coupling. The insight into the molecular origins of interface effects via dual-interface regulation in the framework of charge hopping offers new development paths for developing advanced energy materials with tailored electrical properties.

Accessing renewable magnetic cellulose nanofiber adsorbent to enhance separation efficiency for adsorption and recovery of Cd2

To address the issue of toxic cadmium pollution and meet the need for rapid separation from water body, a magnetic bio-composite material, marked as CFeMg, was prepared via a facile method. It explicitly includes components of cellulose nanofiber (CNF), Fe3O4 and Mg (OH)2. The microstructures and morphology were characterized and analyzed using XRD, FT-IR, SEM, and TEM. CNF was chemically coupled by Fe3O4, which together constructed the overall layered structure. Between layers were Mg(OH)2 flakes attached. While dealing with Cd2+, qmax of the best sample reached 361.5 mg g-1 with high adsorption efficiency. The roles of three components were explored and the adsorption mechanism was proposed. Assisted by magnetic CNF, it only took 3 min to efficiently and completely salvage the spent CFeMg sample from water after adsorption. Due to its high adsorption capacity and facile recovery performance, the prepared composite has promising application as water treatment.

Wood and Cellulose: the Most Sustainable Advanced Materials for Past, Present, and Future Civilizations

Wood, with its constituent building block cellulose, is by far the most common biomaterial on the planet and has been the most important material used by humans to establish civilization. If there is one single biomaterial that should be studied and used by materials scientists across disciplines to achieve a sustainable future, it is cellulose. This perspective provides insights for the general materials science community about the unique properties of wood and cellulose and how they may be used in advanced sustainable materials to make a substantial societal impact. The focus is on sawn wood or cellulose fibers produced at scale by industry and the more recent cellulosic nanomaterials, highlighting the areas where these cellulose-based materials can be valorized into higher-order functions. Numerous articles have comprehensively reviewed different areas where cellulose is currently used in advanced materials science. The objective here is to provide general insight for all material scientists and to provide the opinions about the areas in which cellulose and wood have the largest potential to make a significant societal impact, especially to realize next-generation sustainable materials for construction, food, water, energy, and information. Discussing key areas where future research is needed to open avenues toward a more sustainable future is ended.

Cellulose consolidated with polyethylene glycol: The nanoscale mechanisms revealed by hybrid Monte Carlo/molecular dynamics modeling

Polyethylene glycol (PEG) consolidation treatment is a widely used conservation strategy for wooden culture relics. However, the consolidation mechanism of PEG is still open to interpretation. PEG-cellulose, the representative component of wood cell wall, interactions are governed by various coupled multi-scale mechanisms which require nano-scale investigation. In this study, a hybrid molecular dynamics and grand canonical Monte Carlo (MD/GCMC) simulation combined with rule of mixture (RoM) analyses are employed to reveal the underlying mechanisms of PEG-induced consolidation. We found that PEG200 reduces moisture adsorption and swelling at museological conditions, confirming its consolidation effect. At high PEG content, a crossover behavior is identified at humid conditions (RH > 80) where excessive sorption and swelling are observed surpassing the untreated sample. The molecular modeling results are found to be consistent with experimental observations. Furthermore, the structural and mechanical properties of the hydrated samples are assessed by examining the porosity distribution, mechanical properties, and hydrogen bonding network. Results indicate mechanical softening induced by PEG treatment. A modified mixture model is proposed based on molecular modeling results that incorporate sorption and swelling coupling, porosity filling and mechanical softening behaviors. Two key mechanisms are identified explaining the consolidation effect of PEG: first, the PEG fills the porosities of amorphous structure thus diminishing sorption sites; second, the polymer structure prohibits PEG from further swelling thus constraining water sorption. The model and theoretical framework can serve as a guide for the design of novel consolidant materials by identifying the key molecular features of an ideal consolidant.

Multiscale dynamics and molecular mobility in cellulose-rich materials

Cellulose, an abundant biopolymer in nature as a structural component of plant cell walls, has a native semi-crystalline structure in which the arrangement of amorphous-crystalline domains governs its key properties such as mechanical and physico-chemical properties. The performance of the material in different situations is shaped by molecular mobility, which affects attributes such as mechanical properties, chemical reactivity, and water absorption. Nevertheless, it is difficult to investigate experimentally the structural and dynamic properties of cellulose-rich materials. This is especially the case for the glass transition, which impacts its quality and properties. This experimental challenge is notably evidenced by the considerable variability in data across the literature. The purpose of this study is to offer a comprehensive multi-scale exploration of dynamics within cellulose-rich materials, emphasizing literature data on cellulose glass transition and molecular relaxations, and providing insights into methods for characterizing their physical state and underscoring the impact of water-cellulose interactions on molecular mobility in these systems. The promising results obtained using multiple approaches bring out the importance of combining methods to achieve a more accurate and detailed understanding of the complex thermal transition in cellulose materials, particularly when considering the influence of water on their thermal dynamics and properties.

Advancing plant cell wall modelling: Atomistic insights into cellulose, disordered cellulose, and hemicelluloses - A review

The complexity of plant cell walls on different hierarchical levels still impedes the detailed understanding of biosynthetic pathways, interferes with processing in industry and finally limits applicability of cellulose materials. While there exist many challenges to readily accessing these hierarchies at (sub-) angström resolution, the development of advanced computational methods has the potential to unravel important questions in this field. Here, we summarize the contributions of molecular dynamics simulations in advancing the understanding of the physico-chemical properties of natural fibres. We aim to present a comprehensive view of the advancements and insights gained from molecular dynamics simulations in the field of carbohydrate polymers research. The review holds immense value as a vital reference for researchers seeking to undertake atomistic simulations of plant cell wall constituents. Its significance extends beyond the realm of molecular modeling and chemistry, as it offers a pathway to develop a more profound comprehension of plant cell wall chemistry, interactions, and behavior. By delving into these fundamental aspects, the review provides invaluable insights into future perspectives for exploration. Researchers within the molecular modeling and carbohydrates community can greatly benefit from this resource, enabling them to make significant strides in unraveling the intricacies of plant cell wall dynamics.

How Many Glucan Chains Form Plant Cellulose Microfibrils? A Mini Review

Assessing the number of glucan chains in cellulose microfibrils (CMFs) is crucial for understanding their structure-property relationships and interactions within plant cell walls. This Review examines the conclusions and limitations of the major experimental techniques that have provided insights into this question. Small-angle X-ray and neutron scattering data predominantly support an 18-chain model, although analysis is complicated by factors such as fibril coalescence and matrix polysaccharide associations. Solid-state nuclear magnetic resonance (NMR) spectroscopy allows the estimation of the CMF width from the ratio of interior to surface glucose residues. However, there is uncertainty in the assignment of NMR spectral peaks to surface or interior chains. Freeze-fracture transmission electron microscopy images show cellulose synthase complexes to be "rosettes" of six lobes each consistent with a trimer of cellulose synthase enzymes, consistent with the synthesis of 18 parallel glucan chains in the CMF. Nevertheless, the number of chains in CMFs remains to be conclusively demonstrated.

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.

Elucidation of temperature-induced water structuring on cellulose surfaces for environmental and energy sustainability

Optimizing drying energy in the forest products industry is critical for integrating lignocellulosic feedstocks across all manufacturing sectors. Despite substantial efforts to reduce thermal energy consumption during drying, further enhancements are possible. Cellulose, the main component of forest products, is Earth's most abundant biopolymer and a promising renewable feedstock. This study employs all-atom molecular dynamics (MD) simulations to explore the structural dynamics of a small Iβ-cellulose microcrystallite and surrounding water layers during drying. Molecular and atomistic profiles revealed localized water near the cellulose surface, with water structuring extending beyond 8 Å into the water bulk, influencing solvent-accessible surface area and solvation energy. With increasing temperature, there was a ∼20 % reduction in the cellulose surface available for interaction with water molecules, and a ∼22 % reduction in solvation energy. The number of hydrogen bonds increased with thicker water layers, facilitated by a "bridging" effect. Electrostatic interactions dominated the intermolecular interactions at all temperatures, creating an energetic barrier that hinders water removal, slowing the drying processes. Understanding temperature-dependent cellulose-water interactions at the molecular level will help in designing novel strategies to address drying energy consumption, advancing the adoption of lignocellulosics as viable manufacturing feedstocks.

The nonlinear mechanics of highly extensible plant epidermal cell walls

Plant epidermal cell walls maintain the mechanical integrity of plants and restrict organ growth. Mechanical analyses can give insights into wall structure and are inputs for mechanobiology models of plant growth. To better understand the intrinsic mechanics of epidermal cell walls and how they may accommodate large deformations during growth, we analyzed a geometrically simple material, onion epidermal strips consisting of only the outer (periclinal) cell wall, ~7 μm thick. With uniaxial stretching by >40%, the wall showed complex three-phase stress-strain responses while cyclic stretching revealed reversible and irreversible deformations and elastic hysteresis. Stretching at varying strain rates and temperatures indicated the wall behaved more like a network of flexible cellulose fibers capable of sliding than a viscoelastic composite with pectin viscosity. We developed an analytic framework to quantify nonlinear wall mechanics in terms of stiffness, deformation, and energy dissipation, finding that the wall stretches by combined elastic and plastic deformation without compromising its stiffness. We also analyzed mechanical changes in slightly dehydrated walls. Their extension became stiffer and more irreversible, highlighting the influence of water on cellulose stiffness and sliding. This study offers insights into the structure and deformation modes of primary cell walls and presents a framework that is also applicable to tissues and whole organs.

Strong, Lightweight, and Shape-Memory Bamboo-Derived All-Cellulose Aerogels for Versatile Scaffolds of Sustainable Multifunctional Materials

Strong, lightweight, and shape-memory cellulose aerogels have great potential in multifunctional applications. However, achieving the integration of these features into a cellulose aerogel without harsh chemical modifications and the addition of mechanical enhancers remains challenging. In this study, a strong, lightweight, and water-stimulated shape-memory all-cellulose aerogel (ACA) is created using a combination strategy of partial dissolution and unidirectional freezing from bamboo. Benefiting from the firm architecture of cellulose microfibers bridging cellulose nanofibers /regenerated cellulose aggregated layers and the bonding of different cellulose crystal components (cellulose Iβ and cellulose II), the ACA, with low density (60.74 mg cm-3 ), possesses high compressive modulus (radial section: 1.2 MPa, axial section: 0.96 MPa). Additionally, when stimulated with water, the ACA exhibits excellent shape-memory features, including highly reversible compression-resilience and instantaneous fold-expansion behaviors. As a versatile scaffold, ACA can be integrated with hydroxyapatite, carboxyl carbon nanotubes, and LiCl, respectively, via a simple impregnation method to yield functionalized cellulose composites for applications in thermal insulation, electromagnetic interference shielding, and piezoresistive sensors. This study provides inspiration and a reliable strategy for the elaborately structural design of functional cellulose aerogels endows application prospects in various multifunction opportunities.

Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation

A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3 C2 Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm-1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.

Elastoplastic behavior of anisotropic, physically crosslinked hydrogel networks comprising stiff, charged fibrils in an electrolyte

Fibrillar hydrogels are remarkably stiff, low-density networks that can hold vast amounts of water. These hydrogels can easily be made anisotropic by orienting the fibrils using different methods. Unlike the detailed and established descriptions of polymer gels, there is no coherent theoretical framework describing the elastoplastic behavior of fibrillar gels, especially concerning anisotropy. In this work, the swelling pressures of anisotropic fibrillar hydrogels made from cellulose nanofibrils were measured in the direction perpendicular to the fibril alignment. This experimental data was used to develop a model comprising three mechanical elements representing the network and the osmotic pressure due to non-ionic and ionic surface groups on the fibrils. At low solidity, the stiffness of the hydrogels was dominated by the ionic swelling pressure governed by the osmotic ingress of water. Fibrils with different functionality show the influence of aspect ratio, chemical functionality, and the remaining amount of hemicelluloses. This general model describes physically crosslinked hydrogels comprising fibrils with high flexural rigidity - that is, with a persistence length larger than the mesh size. The experimental technique is a framework to study and understand the importance of fibrillar networks for the evolution of multicellular organisms, like plants, and the influence of different components in plant cell walls.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Behavior of the Flexural Strength of Hemp/Polypropylene Composites: Evaluation of the Intrinsic Flexural Strength of Untreated Hemp Strands

The growing demand for plant fiber-reinforced composites offers new opportunities to compete against glass fiber (GF)-reinforced composites, but their performance must be assessed, revised, and improved as much as possible. This work reports on the production and the flexural strength of composites from polypropylene (PP) and hemp strands (20-50 wt.%), using maleic anhydride-grafted PP (MAPP) as a compatibilizer. A computational assessment of the reaction between cellulose and MAPP suggested the formation of only one ester bond per maleic anhydride unit as the most stable product. We determined the most favorable MAPP dosage to be 0.06 g per gram of fiber. The maximum enhancement in flexural strength that was attained with this proportion of MAPP was 148%, corresponding to the maximum fiber load. The modified rule of mixtures and the assumption of similar coupling factors for tensile and flexural strength allowed us to estimate the intrinsic flexural strength of hemp strands as 953 ± 116 MPa. While falling short of the values for sized GF (2415 MPa), the reinforcement efficiency parameter of the natural fibers (0.209) was found to be higher than that of GF (0.045).