Pretreatment to Retrieve Xylose and Xylooligosaccharides by HCl Gas Directly from Biomass.

In this study, anhydrous hydrogen chloride gas was employed to selectively hydrolyze hemicellulose from aspen wood flour utilizing a gas-solid system. Selectivity toward hemicellulose was achieved by adjusting the acid concentration inside wood flour to 36% during gas hydrolysis, so only hemicellulose and disordered cellulose would be degraded during hydrolysis. Process parameters included the moisture content of the aspen wood flour (20%, 40%, and 60%) and reaction times from 30 min to 24 h. The optimal reaction conditions for the production of xylose and xylooligosaccharides was achieved with 40% moisture content and 6 h reaction time. Under these parameters, it was possible to retrieve 84% of the available xylan from aspen wood flour with only 1% glucan degradation.

Innovations in hydrogel-based manufacturing: A comprehensive review of direct ink writing technique for biomedical applications.

Direct ink writing (DIW) stands as a pioneering additive manufacturing technique that holds transformative potential in the field of hydrogel fabrication. This innovative approach allows for the precise deposition of hydrogel inks layer by layer, creating complex three-dimensional structures with tailored shapes, sizes, and functionalities. By harnessing the versatility of hydrogels, DIW opens up possibilities for applications spanning from tissue engineering to soft robotics and wearable devices. This comprehensive review investigates DIW as applied to hydrogels and its multifaceted applications. The paper introduces a diverse range of printing techniques while providing a thorough exploration of DIW for hydrogel-based printing. The investigation aims to explain the progress made, challenges faced, and potential trajectories that lie ahead for DIW in hydrogel-based manufacturing. The fundamental principles underlying DIW are carefully examined, specifically focusing on rheological attributes and printing parameters, prompting a comprehensive survey of the wide variety of hydrogel materials. These encompass both natural and synthetic variations, all of which can be effectively harnessed for this purpose. Furthermore, the review explores the latest applications of DIW for hydrogels in biomedical areas, with a primary focus on tissue engineering, wound dressing, and drug delivery systems. The document not only consolidates the existing state of DIW within the context of hydrogel-based manufacturing but also charts potential avenues for further research and innovative breakthroughs.

Adsorption of Polystyrene from Theta Condition on Cellulose and Silica Studied by Quartz Crystal Microbalance.

Adsorption of hydrophobic polymers from a nonpolar solvent medium is an underutilized tool for modification of surfaces, especially of soft matter. Adsorption of polystyrene (PS) from a theta solvent (50/50 vol % toluene/heptane) on ultrathin model films of cellulose was studied with a quartz crystal microbalance with dissipation monitoring (QCM-D), using three different PS grades with monodisperse molecular weights (Mws). Comparison of cellulose to silica as an adsorbent was presented. Adsorption on both surfaces was mainly irreversible under the studied conditions. Characteristically to polymer monolayer formation, the mass of the adsorbing polymer increased with its Mw. The initial step of the layer formation was similar on both surfaces, but silica showed a stronger tendency for the formation of a loosely bound overlayer upon molecular rearrangements as the adsorption process proceeded. Despite the slightly less extended layers formed on cellulose at increasing Mw values, the overall thickness of the adsorbing wet layers on both surfaces was of the similar order of magnitude as the radius of gyration of the adsorbate molecule. Decent degree of hydrophobization of cellulose could be reached with all studied PS grades when the time allowed for adsorption was sufficient. QCM-D, a method conventionally utilized for studying aqueous systems, turned out to be a suitable tool for studying the adsorption process of hydrophobic polymers on soft polymeric matter such as cellulose taking place in a nonpolar solvent environment.

Production of Water-Soluble Carbohydrates from Aspen Wood Flour with Hydrogen Chloride Gas.

The aim of this study was to optimize the reaction conditions for concentrated acid hydrolysis of aspen wood flour by employing anhydrous hydrogen chloride gas to produce fermentable sugars. Gas hydrolysis with HCl was conducted both with and without temperature control during hydrolysis under a relatively low pressure of 0.1 MPa. Process parameters for HCl gas hydrolysis included the moisture content of aspen wood flour (0.7-50%) and reaction time under pressure (30 min to 24 h). In addition, liquid-phase hydrolysis with concentrated hydrochloric acid was conducted in concentrations of 32-42% and 15 min to 24 h reaction times for comparison with the gas-phase process. The highest yields (>90%) for water-soluble carbohydrates from aspen wood flour were achieved with temperature-controlled gas hydrolysis using 50% moisture content and 2 h total reaction time, which is in line with the previous research and comparable to hydrolysis with concentrated (42%) hydrochloric acid.

Assessment of the Alga Cladophora glomerata as a Source for Cellulose Nanocrystals.

Nanocellulose is isolated from cellulosic fibers and exhibits many properties that macroscale cellulose lacks. Cellulose nanocrystals (CNCs) are a subcategory of nanocellulose made of stiff, rodlike, and highly crystalline nanoparticles. Algae of the order Cladophorales are the source of the longest cellulosic nanocrystals, but manufacturing these CNCs is not well-studied. So far, most publications have focused on the applications of this material, with the basic manufacturing parameters and material properties receiving little attention. In this article, we investigate the entirety of the current manufacturing process from raw algal biomass (Cladophora glomerata) to the isolation of algal cellulose nanocrystals. Yields and cellulose purities are investigated for algal cellulose and the relevant process intermediates. Furthermore, the effect of sulfuric acid hydrolysis, which is used to convert cellulose into CNCs and ultimately determines the material properties and some of the sustainability aspects, is examined and compared to literature results on wood cellulose nanocrystals. Long (>4 µm) CNCs form a small fraction of the overall number of CNCs but are still present in measurable amounts. The results define essential material properties for algal CNCs, simplifying their future use in functional cellulosic materials.

Thermodynamically controlled multiphase separation of heterogeneous liquid crystal colloids.

Phase separation is a universal physical transition process whereby a homogeneous mixture splits into two distinct compartments that are driven by the component activity, elasticity, or compositions. In the current work, we develop a series of heterogeneous colloidal suspensions that exhibit both liquid-liquid phase separation of semiflexible binary polymers and liquid crystal phase separation of rigid, rod-like nanocellulose particles. The phase behavior of the multicomponent mixture is controlled by the trade-off between thermodynamics and kinetics during the two transition processes, displaying cholesteric self-assembly of nanocellulose within or across the compartmented aqueous phases. Upon thermodynamic control, two-, three-, and four-phase coexistence behaviors with rich liquid crystal stackings are realized. Among which, each relevant multiphase separation kinetics shows fundamentally different paths governed by nucleation and growth of polymer droplets and nanocellulose tactoids. Furthermore, a coupled multiphase transition can be realized by tuning the composition and the equilibrium temperature, which results in thermotropic behavior of polymers within a lyotropic liquid crystal matrix. Finally, upon drying, the multicomponent mixture undergoes a hierarchical self-assembly of nanocellulose and polymers into stratified cholesteric films, exhibiting compartmentalized polymer distribution and anisotropic microporous structure.

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.

Efficient Isolation Method for Highly Charged Phosphorylated Cellulose Nanocrystals.

Phosphorylation of cellulose nanocrystals (CNCs) has remained a marginal activity despite the undisputed application potential in flame-retardant materials, sustainable high-capacity ion-exchange materials, or substrates for biomineralization among others. This is largely due to strenuous extraction methods prone to a combination of poor reproducibility, low degrees of substitution, disappointing yields, and impractical reaction sequences. Here, we demonstrate an improved methodology relying on the modification routines for phosphorylated cellulose nanofibers and hydrolysis by gaseous HCl to isolate CNCs. This allows us to overcome the aforementioned shortcomings and to reliably and reproducibly extract phosphorylated CNCs with exceptionally high surface charge (∼2000 mmol/kg) in a straightforward routine that minimizes water consumption and maximizes yields. The CNCs were characterized by NMR, ζpotential, conductometric titration, thermogravimetry, elemental analysis, wide-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy.

Engineered Protein Copolymers for Heparin Neutralization and Detection.

Heparin is a widely applied anticoagulant agent. However, in clinical practice, it is of vital importance to reverse its anticoagulant effect to restore the blood-clotting cascade and circumvent side effects. Inspired by protein cages that can encapsulate and protect their cargo from surroundings, we utilize three designed protein copolymers to sequester heparin into inert nanoparticles. In our design, a silk-like sequence provides cooperativity between proteins, generating a multivalency effect that enhances the heparin-binding ability. Protein copolymers complex heparin into well-defined nanoparticles with diameters below 200 nm. We also develop a competitive fluorescent switch-on assay for heparin detection, with a detection limit of 0.01 IU mL-1 in plasma that is significantly below the therapeutic range (0.2-8 IU mL-1). Moreover, moderate cytocompatibility is demonstrated by in vitro cell studies. Therefore, such engineered protein copolymers present a promising alternative for neutralizing and sensing heparin, but further optimization is required for in vivo applications.

Degradation of cellulose polymorphs into glucose by HCl gas with simultaneous suppression of oxidative discoloration.

As cellulose is the main polysaccharide in biomass, its degradation into glucose is a major undertaking in research concerning biofuels and bio-based platform chemicals. Here, we show that pressurized HCl gas is able to efficiently hydrolyze fibers of different crystalline forms (polymorphs) of cellulose when the water content of the fibers is increased to 30-50 wt%. Simultaneously, the harmful formation of strongly chromophoric humins can be suppressed by a simple addition of chlorite into the reaction system. 50-70 % glucose yields were obtained from cellulose I and II polymorphs while >90 % monosaccharide conversion was acquired from cellulose IIIII after a mild post-hydrolysis step. Purification of the products is relatively unproblematic from a gas-solid mixture, and a gaseous catalyst is easier to recycle than the aqueous counterpart. The results lay down a basis for future practical solutions in cellulose hydrolysis where side reactions are controlled, conversion rates are efficient, and the recovery of products and reagents is effortless.

The Impact of Surface Charges of Carboxylated Cellulose Nanofibrils on the Water Motions in Hydrated Films.

Cellulose nanofibrils (CNFs) with carboxylated surface ligands are a class of materials with tunable surface functionality, good mechanical properties, and bio-/environmental friendliness. They have been used in many applications as scaffold, reinforcing, or functional materials, where the interaction between adsorbed moisture and the CNF could lead to different properties and structures and become critical to the performance of the materials. In this work, we exploited multiple experimental methods to study the water movement in hydrated films made of carboxylated CNFs prepared by TEMPO oxidation with two different surface charges of 600 and 1550 µmol·g-1. A combination of quartz crystal microbalance with dissipation (QCM-D) and small-angle X-ray scattering (SAXS) shows that both the surface charge of a single fibril and the films' network structure contribute to the moisture uptake. The films with 1550 µmol·g-1 surface charges take up twice the amount of moisture per unit mass, leading to the formation of nanostructures with an average radius of gyration of 2.1 nm. Via the nondestructive quasi-elastic neutron scattering (QENS), a faster motion is explained as a localized movement of water molecules inside confined spheres, and a slow diffusive motion is found with the diffusion coefficient close to bulk water at room temperature via a random jump diffusion model and regardless of the surface charge in films made from CNFs.

Effect of Moisture on Polymer Deconstruction in HCl Gas Hydrolysis of Wood.

The HCl gas system previously used to produce cellulose nanocrystals was applied on Scots pine wood, aiming at a controlled deconstruction of its macrostructure while understanding the effect on its microstructure. The HCl gas treatments resulted in a well-preserved cellular structure of the wood. Differences in wood initial moisture content (iMC) prior to HCl gas treatment played a key role in hydrolysis rather than the studied range of exposure time to the acidic gas. Higher iMCs were correlated with a higher degradation of hemicellulose, while crystalline cellulose microfibrils were not largely affected by the treatments. Remarkably, the hydrogen-deuterium exchange technique showed an increase in accessible OH group concentration at higher iMCs, despite the additional loss in hemicelluloses. Unrelated to changes in the accessible OH group concentration, the HCl gas treatment reduced the concentration of absorbed D2O molecules.

Assessing Fire-Damage in Historical Papers and Alleviating Damage with Soft Cellulose Nanofibers.

The conservation of historical paper objects with high cultural value is an important societal task. Papers that have been severely damaged by fire, heat, and extinguishing water, are a particularly challenging case, because of the complexity and severity of damage patterns. In-depth analysis of fire-damaged papers, by means of examples from the catastrophic fire in a 17th-century German library, shows the changes, which proceeded from the margin to the center, to go beyond surface charring and formation of hydrophobic carbon-rich layers. The charred paper exhibits structural changes in the nano- and micro-range, with increased porosity and water sorption. In less charred areas, cellulose is affected by both chain cleavage and cross-linking. Based on these results and conclusions with regard to adhesion of auxiliaries, a stabilization method is developed, which coats the damaged paper with a thin layer of cellulose nanofibers. It enables the reliable preservation of the paper and-most importantly-retrieval of the contained historical information: the nanofibers form a flexible, transparent film on the surface and adhere strongly to the damaged matrix, greatly reducing its fragility, giving it stability, and enabling digitization and further handling.

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.

Tuning the Porosity, Water Interaction, and Redispersion of Nanocellulose Hydrogels by Osmotic Dehydration.

Osmotic dehydration (OD) was introduced as a method to reproducibly tune the water content and porosity of cellulose nanofiber (CNF) hydrogels. The hierarchical porosity was followed by electron microscopy (pores with a >100 µm diameter) and thermoporosimetry (mesopores), together with mechanical testing, in hydrogels with solid contents ranging from 0.7 to 12 wt %. Furthermore, a reciprocal correlation between proton conductivity and the ratio of water bound to the nanocellulose network was established, suggesting the potential of these systems toward tunable energy materials.

Solid-state polymer adsorption for surface modification: The role of molecular weight.

HYPOTHESIS: Solid-state polymer adsorption offers a distinct approach for surface modification. These ultrathin, so-called Guiselin layers can easily be obtained by placing a polymer melt in contact with an interface, followed by a removal of the non-adsorbed layer with a good solvent. While the mechanism of formation has been well established for Guiselin layers, their stability, crucial from the perspective of materials applications, is not. The stability is a trade-off in the entropic penalty between cooperative detachment of the number of segments directly adsorbed on the substrate and consecutively pinned monomers. EXPERIMENTS: Experimental model systems of Guiselin layers of polystyrene (PS) on silicon wafers with native oxide layer on top were employed. The stability of the adsorbed layers was studied as a function of PS molecular weight and polydispersibility by various microscopic and spectroscopic tools as well as quasi-static contact angle measurements. FINDINGS: Adsorbed layers from low molecular weight PS were disrupted with typical spinodal decomposition patterns whereas high molecular weight (>500 kDa) PS resulted in stable, continuous layers. Moreover, we show that Guiselin layers offer an enticing way to modify a surface, as demonstrated by adsorbed PS that imparts a hydrophobic character to initially hydrophilic silicon wafers.

Tuning the Physicochemical Properties of Cellulose Nanocrystals through an In Situ Oligosaccharide Surface Modification Method.

The trend to replace petroleum-based products with sustainable alternatives has shifted research efforts toward plant-based materials such as cellulose nanocrystals (CNCs). CNCs show promise in numerous applications (e.g., composites and rheological modifiers); however, maximizing their performance often requires surface modifications with complex chemistries and purification steps. Presented here is a novel surface modification method with the potential to tune CNC properties through the in situ deposition of cellulose phosphate oligosaccharides during CNC production. This was achieved by leveraging the selective solubility of oligosaccharides, which are soluble at a low pH (during the CNC hydrolysis) yet become insoluble and precipitate onto CNC surfaces upon increasing pH during quenching. Oligosaccharide-coated CNCs demonstrated subtle changes including higher surface charge densities and lower water adsorption capacities and viscosities than their unmodified counterparts. CNC surface coverage was tuned by controlling the oligosaccharide degree of polymerization. Overall, this fundamental study introduces an easily scalable modification route that opens the door for expanded CNC functionality and applications.

Challenges in Synthesis and Analysis of Asymmetrically Grafted Cellulose Nanocrystals via Atom Transfer Radical Polymerization.

When cellulose nanocrystals (CNCs) are isolated from cellulose microfibrils, the parallel arrangement of the cellulose chains in the crystalline domains is retained so that all reducing end-groups (REGs) point to one crystallite end. This permits the selective chemical modification of one end of the CNCs. In this study, two reaction pathways are compared to selectively attach atom-transfer radical polymerization (ATRP) initiators to the REGs of CNCs, using reductive amination. This modification further enabled the site-specific grafting of the anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) from the CNCs. Different analytical methods, including colorimetry and solution-state NMR analysis, were combined to confirm the REG-modification with ATRP-initiators and PSS. The achieved grafting yield was low due to either a limited conversion of the CNC REGs or side reactions on the polymerization initiator during the reductive amination. The end-tethered CNCs were easy to redisperse in water after freeze-drying, and the shear birefringence of colloidal suspensions is maintained after this process.

Directed Assembly of Cellulose Nanocrystals in Their Native Solid-State Template of a Processed Fiber Cell Wall.

Nanoparticle assembly is intensely surveyed because of the numerous applications within fields such as catalysis, batteries, and biomedicine. Here, directed assembly of rod-like, biologically derived cellulose nanocrystals (CNCs) within the template of a processed cotton fiber cell wall, that is, the native origin of CNCs, is reported. It is a system where the assembly takes place in solid state simultaneously with the top-down formation of the CNCs via hydrolysis with HCl vapor. Upon hydrolysis, cellulose microfibrils in the fiber break down to CNCs that then pack together, resulting in reduced pore size distribution of the original fiber. The denser packing is demonstrated by N2 adsorption, water uptake, thermoporometry, and small-angle X-ray scattering, and hypothetically assigned to attractive van der Waals interactions between the CNCs.