Structural Order in Cellulose Thin Films Prepared from a Trimethylsilyl Precursor

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 Resilient is Wood Xylan to Enzymatic Degradation in a Matrix with Kraft Lignin?

Despite the potential of lignocellulose in manufacturing value-added chemicals and biofuels, its efficient biotechnological conversion by enzymatic hydrolysis still poses major challenges. The complex interplay between xylan, cellulose, and lignin in fibrous materials makes it difficult to assess underlying physico- and biochemical mechanisms. Here, we reduce the complexity of the system by creating matrices of cellulose, xylan, and lignin, which consists of a cellulose base layer and xylan/lignin domains. We follow enzymatic degradation using an endoxylanase by high-speed atomic force microscopy and surface plasmon resonance spectroscopy to obtain morphological and kinetic data. Fastest reaction kinetics were observed at low lignin contents, which were related to the different swelling capacities of xylan. We demonstrate that the complex processes taking place at the interfaces of lignin and xylan in the presence of enzymes can be monitored in real time, providing a future platform for observing phenomena relevant to fiber-based systems.

Interplay of electrolyte concentration and molecular weight of polyDADMAC on cellulose surface adsorption

Cationic polyelectrolytes (PEs) are commonly used additives in manufacturing of cellulose based products such as regenerated fibers and paper to tailor their product properties. Here we are studying the adsorption of poly(diallyldimethylammonium chloride), PD, on cellulose, using in situ surface plasmon resonance spectroscopy (SPR) measurements. We employ model surfaces from regenerated cellulose xanthate (CX) and trimethylsilyl cellulose (TMSC), mimicking industrially relevant regenerated cellulose substrates. The effects of the PDs molecular weight were strongly depending on the ionic strength and type of electrolyte (NaCl vs CaCl₂). Without electrolytes, the adsorption was monolayer-type, i.e. independent of molecular weight. At moderate ionic strength, adsorption increased due to more pronounced PE coiling, while at high ionic strength electrostatic shielding strongly reduced adsorption of PDs. Results exhibited pronounced differences for the chosen substrates (cellulose regenerated from xanthate (CX_reg) vs. regenerated from trimethylsilyl cellulose, TMSC_reg). Consistently higher adsorbed amounts of the PD were determined on CX_reg surfaces compared TMSC. This can be attributed to a more negative zeta potential, a higher AFM roughness and a higher degree of swelling (investigated by QCM-D) of the CX_reg substrates.

A computational study of cellulose regeneration: Coarse-grained molecular dynamics simulations

Understanding the microscopic mechanisms of regeneration of cellulose is prerequisite for engineering and controlling its material properties. In this paper, we performed coarse-grained Martini 3 molecular dynamics simulations of cellulose regeneration at a scale comparable to the experiments. The X-ray diffraction (XRD) curves were monitored to follow the structural changes of regenerated cellulose and trace formation of cellulose sheets and crystallites. The calculated coarse-grained morphologies of regenerated cellulose were backmapped to atomistic ones. After the backmapping we find that the regenerated coarse-grained cellulose structures calculated for both topology parameters of cellulose I_β and cellulose II/III, are transformed to cellulose II, where the calculated XRD curves exhibit the main peak at approximately 20-21 degrees, corresponding to the (110)/(020) planes of cellulose II. This result is in good quantitative agreement with the available experimental observations.

Humidity Response of Cellulose Thin Films

Cellulose-water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.

Understanding the Drying Behavior of Regenerated Cellulose Gel Beads: The Effects of Concentration and Nonsolvents

The drying behavior of regenerated cellulose gel beads swollen with different nonsolvents (e.g., water, ethanol, water/ethanol mixtures) is studied in situ on the macroscopic scale with an optical microscope as well as on nanoscale using small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques. Depending on the cellulose concentration, the structural evolution of beads during drying follows one of three distinct regimes. First, when the cellulose concentration is lower than 0.5 wt %, the drying process comprises three steps and, regardless of the water/ethanol mixture composition, a sharp structural transition corresponding to the formation of a cellulose II crystalline structure is observed. Second, when the cellulose concentration is higher than 5.0 wt %, a two-step drying process is observed and no structural transition occurs for any of the beads studied. Third, when the cellulose concentration is between 0.5 and 5.0 wt %, the drying process is dependent on the nonsolvent composition. A three-step drying process takes place for beads swollen with water/ethanol mixtures with a water content higher than 20%, while a two-step drying process is observed when the water content is lower than 20%. To describe the drying behavior governed by the cellulose concentration and nonsolvent composition, a simplified phase diagram is proposed.

Fundamental aspects of the non-covalent modification of cellulose via polymer adsorption

The increasing need for new material applications based on cellulose demands increased functional diversity and thus new functionalisation/modification approaches. The non-covalent modification of cellulose fibres via the adsorption of functional polymers has emerged as a promising route for tailoring the properties of material. This review focuses on fundamental aspects of polymer adsorption on cellulose surfaces, where the adsorption of polyelectrolytes and non-polyelectrolytes are treated separately. Adsorption studies on model surfaces as well as cellulose macro-fibres are reviewed. A correlation of the adsorption findings with the Scheutjens-Fleer polymer adsorption theory is provided, allowing the fundamentals behind the polymer adsorption phenomenon and its context in utilization of cellulose fibres to be understood.

Nanocellulose-Assisted Thermally Induced Growth of Silver Nanoparticles for Optical Applications

Optically responsive materials are present in everyday life, from screens to sensors. However, fabricating large-area, fossil-free materials for functional biocompatible applications is still a challenge today. Nanocelluloses from various sources, such as wood, can provide biocompatibility and are emerging candidates for templating organic optoelectronics. Silver (Ag) in its nanoscale form shows excellent optical properties. Herein, we combine both materials using thin-film large-area spray-coating to study the fabrication of optical response applications. We characterize the Ag nanoparticle formation by X-ray scattering and UV-vis spectroscopy in situ during growth on the nanocellulose template. The morphology and optical properties of the nanocellulose film are compared to the rigid reference surface SiO₂. Our results clearly show the potential to tailor the energy band gap of the resulting hybrid material.

Interactions and Dissociation Constants of Galactomannan Rendered Cellulose Films with Concavalin A by SPR Spectroscopy

Interactions of biomolecules at interfaces are important for a variety of physiological processes. Among these, interactions of lectins with monosaccharides have been investigated extensively in the past, while polysaccharide-lectin interactions have scarcely been investigated. Here, we explore the adsorption of galactomannans (GM) extracted from Prosopis affinis on cellulose thin films determined by a combination of multi-parameter surface plasmon resonance spectroscopy (MP-SPR) and atomic force microscopy (AFM). The galactomannan adsorbs spontaneously on the cellulose surfaces forming monolayer type coverage (0.60 ± 0.20 mg·m-2). The interaction of a lectin, Concavalin A (ConA), with these GM rendered cellulose surfaces using MP-SPR has been investigated and the dissociation constant KD (2.1 ± 0.8 × 10-8 M) was determined in a range from 3.4 to 27.3 nM. The experiments revealed that the galactose side chains as well as the mannose reducing end of the GM are weakly interacting with the active sites of the lectins, whereas these interactions are potentially amplified by hydrophobic effects between the non-ionic GM and the lectins, thereby leading to an irreversible adsorption.

Review: Periodate oxidation of wood polysaccharides-Modulation of hierarchies

Periodate oxidation of polysaccharides has transitioned from structural analysis into a modification method for engineered materials. This review summarizes the research on this topic. Fibers, fibrils, crystals, and molecules originating from forests that have been subjected to periodate oxidation can be crosslinked with other entities via the generated aldehyde functionality, that can also be oxidized or reduced to carboxyl or alcohol functionality or used as a starting point for further modification. Periodate-oxidized materials can be subjected to thermal transitions that differ from the native cellulose. Oxidation of polysaccharides originating from forests often features oxidation of structures rather than liberated molecules. This leads to changes in macro, micro, and supramolecular assemblies and consequently to alterations in physical properties. This review focuses on these aspects of the modulation of structural hierarchies due to periodate oxidation.

Macro- and Microstructural Evolution during Drying of Regenerated Cellulose Beads

The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process. However, the drying of cellulose from water follows a more complex process when compared to drying from ethanol. As water swollen beads dried, they went through a structural transition where elongated structures changed to spherical structures and their dimensions increased from 3.6 to 13.5 nm. After complete drying from water, the nanostructures were characterized as a combination of rodlike structures with an approximate size of cellulose monomers (0.5 nm), and spherical aggregates (13.5 nm) without any indication of heterogeneous meso- or microporosity. In addition, WAXS shows that cellulose II hydrate structure appears and transforms to cellulose II during water evaporation, however it is not possible to determine the degree of crystallinity of the beads from the present measurements. This work sheds lights on the structural changes that occur within regenerated cellulose materials during drying and can aid in the design and application of cellulosic materials as fibers, adhesives, and membranes.

Nanocelluloses and Related Materials Applicable in Thermal Management of Electronic Devices: A Review

Owing to formidable advances in the electronics industry, efficient heat removal in electronic devices has been an urgent issue. For thermal management, electrically insulating materials that have higher thermal conductivities are desired. Recently, nanocelluloses (NCs) and related materials have been intensely studied because they possess outstanding properties and can be produced from renewable resources. This article gives an overview of NCs and related materials potentially applicable in thermal management. Thermal conduction in dielectric materials arises from phonons propagation. We discuss the behavior of phonons in NCs as well.