13C NMR assignments of regenerated cellulose from solid-state 2D NMR spectroscopy

Elucidating the structural changes of cellulose molecules and dynamics of Na ions during the crystal transition from cellulose I to II in low temperature and low concentration NaOH solution

Low-concentration alkali treatments at low temperatures facilitate the crystal transition of cellulose I to II. However, the transition mechanism remains unclear. Hence, in this study, we traced the transition using in situ solid-state 13C CP/MAS NMR, WAXS, and 23Na NMR relaxation measurements. In situ solid-state 13C CP/MAS NMR and WAXS measurements revealed that soaking cellulose in NaOH at low temperatures disrupts the intramolecular hydrogen bonds and lowers the crystallinity of cellulose. The dynamics of Na ions (NaOH) play a crucial role in causing these phenomena. 23Na NMR relaxation measurements indicated that the Na-ion correlation time becomes longer during the crystal transition. This transition requires the penetration of Na ions (NaOH) into the cellulose crystal and a reduction in Na-ion mobility, which occurs at low temperatures or high NaOH concentrations. The interactions between cellulose and NaOH disrupt intramolecular hydrogen bonds, inducing a conformational change in the cellulose molecules into a more stable arrangement. This weakens the hydrophobic interactions of cellulose, and facilitates the penetration of NaOH and water into the crystal, leading to the formation of alkali cellulose. Our findings suggest that a strategy to control NaOH dynamics could lead to the discovery of a novel preparation method for cellulose II.

Oxidation with potassium ferrate for the one-pot preparation of carboxylated cellulose II nanocrystals

Cellulose II nanocrystals (CNC II) possess a higher thermal stability and improved emulsifying capability than cellulose I nanocrystals (CNC I) owing to the higher density of their hydrogen bonds and more larger surface areas. Therefore, CNC II exhibit substantial advantages for value-added nanocomposite materials. Current CNC II preparation methods are mainly based on a two-pot reaction involving acid hydrolysis and crystal transformation. In this study, considering the oxidative nature of potassium ferrate (K2FeO4) in an alkaline environment containing a small amount of sodium hypochlorite (NaClO), a one-step and efficient approach was developed for the preparation of carboxyl-bearing CNC II from cotton pulp, affording a maximum CNC II yield of 45.14 %. Atomic force microscopy analysis revealed that the prepared CNCs exhibited a "rod-like" shape with a width of ~7 nm and a length of ~269 nm. The resulting CNC II also exhibited excellent thermal stability (Tonset = 311.4 °C). Furthermore, high-internal-phase Pickering emulsions (HIPPEs) stabilized by CNC II were prepared to stabilize liquid paraffin in the absence of surfactant. The results revealed that CNC II could be used as an effective emulsifier to fabricate the stable and gel-like HIPPEs, and are promising for the preparation of high value-added nanocomposite materials.

Cellulose nanocrystals extracted from rice husk using the formic/peroxyformic acid process: isolation and structural characterization

Cellulose derived from biomass is a renewable resource with numerous applications. Using formic/peroxyformic acid at atmospheric pressure, cellulose nanocrystals (CNC) were isolated from rice husk (RH) in this study. This method was an excellent way to get rid of lignin and hemicelluloses from RH. The cellulose was subsequently acid hydrolyzed by H2SO4 (64%) for 30 minutes at 45 °C. The chemical and microstructure analysis showed that the lignin and hemicellulose contents of raw RH had been eliminated, and the crystallinity content of CNC was 67.16%. According to transmission electron microscopy (TEM) morphological analysis, CNC measured 19 ± 3.3 nm in diameter, 195 ± 24 nm in length, and 10.2 ± 6.8 in aspect ratio. The thermal stability of RH and CNC was also investigated using thermogravimetric analysis (TGA). These encouraging findings demonstrated the potential for reusing RH agricultural waste to create CNC and include nanocomposites as a reinforcing material.

Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Combustion is often difficult to spatially direct or tune associated kinetics-hence a run-away reaction. Coupling pyrolytic chemical transformation to mass transport and reaction rates (Damköhler number), however, we spatially directed ignition with concomitant switch from combustion to pyrolysis (low oxidant). A 'surface-then-core' order in ignition, with concomitant change in burning rate,is therefore established. Herein, alkysilanes grafted onto cellulose fibers are pyrolyzed into non-flammable SiO2 terminating surface ignition propagation, hence stalling flame propagating. Sustaining high temperatures, however, triggers ignition in the bulk of the fibers but under restricted gas flow (oxidant and/or waste) hence significantly low rate of ignition propagation and pyrolysis compared to open flame (Liñán's equation). This leads to inside-out thermal degradation and, with felicitous choice of conditions, formation of graphitic tubes. Given the temperature dependence, imbibing fibers with an exothermically oxidizing synthon (MnCl2 ) or a heat sink (KCl) abets or inhibits pyrolysis leading to tuneable wall thickness. We apply this approach to create magnetic, paramagnetic, or oxide containing carbon fibers. Given the surface sensitivity, we illustrate fabrication of nm- and μm-diameter tubes from appropriately sized fibers.

Emerging Applications of Hydroxypropyl Methylcellulose Acetate Succinate: Different Aspects in Drug Delivery and Its Commercial Potential

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) has multi-disciplinary applications spanning across the development of drug delivery systems, in 3D printing, and in tissue engineering, etc. HPMCAS helps in maintaining the drug in a super-saturated condition by inhibiting its precipitation, thereby increasing the rate and extent of dissolution in the aqueous media. HPMCAS has several distinctive characteristics, such as being amphiphilic in nature, having an ionization pH, and a succinyl and acetyl substitution ratio, all of which are beneficial while developing formulations. This review provides insights regarding the various types of formulations being developed using HPMCAS, including amorphous solid dispersion (ASD), amorphous nanoparticles, dry coating, and 3D printing, along with their applicability in drug delivery and biomedical fields. Furthermore, HPMCAS, compared with other carbohydrate polymers, shows several benefits in drug delivery, including proficiency in imparting stable ASD with a high dissolution rate, being easily processable, and enhancing bioavailability. The various commercially available formulations, regulatory considerations, and key patents containing the HPMCAS have been discussed in this review.

Investigation of cellulose dissolution in morpholinium-based solvents: impact of solvent structural features on cellulose dissolution

A series of N-methylmorpholinium salts with varying N-alkyl chains and Cl-, OAc- and OH- as counter ions have been synthesized and investigated for their ability to dissolve cellulose, aiming at elucidating solvent structural features affecting cellulose dissolution. Synthesis procedures have been developed to, to a high extent, rely on conversions in water and microwave-assisted reactions employing a reduced number of work-up steps and ion-exchange resins that can be regenerated. Water solutions of morpholinium hydroxides proved capable of dissolving cellulose, with those of them possessing alkyl chains longer than ethyl showing surprising dissolution ability at room-temperature. Morpholinium acetates behaved as ionic liquids, and were also capable of dissolving cellulose when combined with DMSO. The obtained cellulose solutions were characterized according to their chemical and colloidal stability using 13C NMR spectroscopy, size exclusion chromatography and flow sweep measurements, while the ethanol coagulates were investigated in terms of crystallinity using solid state NMR. In contrast, the morpholinium chlorides obtained were hygroscopic with high melting points and low solubility in common organic solvents e.g., acetone, DMSO and DMAc, thus lacking the ability to swell or dissolve cellulose.

Structural properties of optically clear bacterial cellulose produced by Komagataeibacter hansenii using arabitol

Bacterial cellulose (BC) exhibits beneficial properties for use in biomedical applications but is limited by its lack of tunable transparency capabilities. To overcome this deficiency, a novel method to synthesize transparent BC materials using an alternative carbon source, namely arabitol, was developed. Characterization of the BC pellicles was performed for yield, transparency, surface morphology, and molecular assembly. Transparent BC was produced using mixtures of glucose and arabitol. Zero percent arabitol pellicles exhibited 25% light transmittance, which increased with increasing arabitol concentration through to 75% light transmittance. While transparency increased, overall BC yield was maintained indicating that the altered transparency may be induced on a micro-scale rather than a macro-scale. Significant differences in fiber diameter and the presence of aromatic signatures were observed. Overall, this research outlines methods for producing BC with tunable optical transparency, while also bringing new insight to insoluble components of exopolymers produced by Komagataeibacter hansenii.

Insights into thermal degradation kinetics and liquid crystalline behavior of cellulose nanocrystals from the waste of Cajanus cajan (pigeon pea)

Cellulose nanocrystals (CNCs) are essential for advancing nanotechnology and modern science. This work used the Cajanus cajan stem, an agricultural waste, as a lignocellulosic mass, which can serve as a supply of CNCs. After extraction from the Cajanus cajan stem, CNCs have been thoroughly characterized. FTIR (Infrared Spectroscopy) and ssNMR (solid-state Nuclear Magnetic Resonance) successfully validated eliminating additional components from the waste stem. The ssNMR and XRD (X-ray diffraction) were utilized to compare the crystallinity index. For structural analysis, the XRD of cellulose I_β was simulated to compare with the extracted CNCs. Various mathematical models inferred thermal stability and its degradation kinetics to ensure its high-end applications. Surface analysis established the rod-like shape of the CNCs. Rheological measurements were performed to gauge the liquid crystalline properties of CNC. The anisotropic liquid crystalline CNCs' birefringence proves that the Cajanus cajan stem is a promising resource for making CNCs for cutting-edge applications.

Strong, Shape-Memory Lignocellulosic Aerogel via Wood Cell Wall Nanoscale Reassembly

Polymer shape-memory aerogels (PSMAs) are prospects in various fields of application ranging from aerospace to biomedicine, as advanced thermal insulators, actuators, or sensors. However, the fabrication of PSMAs with good mechanical performance is challenging and is currently dominated by fossil-based polymers. In this work, strong, shape-memory bio-aerogels with high specific surface areas (up to 220 m²/g) and low radial thermal conductivity (0.042 W/mK) were prepared through a one-step treatment of native wood using an ionic liquid mixture of [MTBD]⁺[MMP]^-/DMSO. The aerogel showed similar chemical composition similar to native wood. Nanoscale spatial rearrangement of wood biopolymers in the cell wall and lumen was achieved, resulting in flexible hydrogels, offering design freedom for subsequent aerogels with intricate geometries. Shape-memory function under stimuli of water was reported. The chemical composition and distribution, morphology, and mechanical performance of the aerogel were carefully studied using confocal Raman spectroscopy, AFM, SAXS/WAXS, NMR, digital image correlation, etc. With its simplicity, sustainability, and the broad range of applicability, the methodology developed for nanoscale reassembly of wood is an advancement for the design of biobased shape-memory aerogels.

Linear Correlation between True Density and Crystallinity of Regenerated and Mercerized Celluloses

Regenerated and mercerized celluloses are widely used in our daily life and industries. Examples include clothes, medical supplies, and separation membranes. In such applications, the true density is an important derived physical quantity for refining the structural designs of regenerated and mercerized celluloses. Here, we report the true density-crystallinity correlation of regenerated and mercerized celluloses. Seven samples were prepared through either dissolution-regeneration or mercerization, and the true density of each sample was measured by helium gas pycnometry. The crystallinity was evaluated by solid-state ¹³C nuclear magnetic resonance spectroscopy based on the ratio of the carbon atoms in the crystallite core to those at crystallite surfaces and in the surrounding amorphous matrix. We found that the true density of regenerated and mercerized celluloses is directly proportional to crystallinity, irrespective of the preparation process. Additionally, the molecular packing density at the crystallite surfaces was found to be similar to that in the amorphous matrix.

Cellulose from Annual Plants and Its Use for the Production of the Films Hydrophobized with Tetrafluoroethylene Telomers

Cellulose HogC was produced by the modified traditional method with 35% yield from the stem of Sosnovsky hogweed and was characterized by elemental analysis, infrared (IR) spectroscopy, powder X-ray diffractometry, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). For HogC, the degree of crystallinity (approximately 70%) and the glass transition temperature (105–108 °C) were determined. It was found that the whiteness characteristic in the case of HogC was 92% and this significate was obtained without a bleaching procedure using chlorine-containing reagents. In this paper, the possibility of hydrophobization of HogC films by treatment with radiation-synthesized telomers of tetrafluoroethylene is shown. It was found that the contact angle of the telomer-treated cellulose film surface depended on the properties of the telomers (the chemical nature of the solvent, and the initial concentration of tetrafluoroethylene) and could reach 140 degrees.

Effect of Ball-Milling Pretreatment of Cellulose on Its Photoreforming for H2 Production

Photoreforming of cellulose is a promising route for sustainable H₂ production. Herein, ball-milling (BM, with varied treatment times of 0.5-24 h) was employed to pretreat microcrystalline cellulose (MCC) to improve its activity in photoreforming over a Pt/TiO₂ catalyst. It was found that BM treatment reduced the particle size, crystallinity index (CrI), and degree of polymerization (DP) of MCC significantly, as well as produced amorphous celluloses (with >2 h treatment time). Amorphous cellulose water-induced recrystallization to cellulose II (as evidenced by X-ray diffraction (XRD) and solid-state NMR analysis) was observed in aqueous media. Findings of the work showed that the BM treatment was a simple and effective pretreatment strategy to improve photoreforming of MCC for H₂ production, mainly due to the decreased particle size and, specifically in aqueous media, the formation of the cellulose II phase from the recrystallization of amorphous cellulose, the extent of which correlates well with the activity in photoreforming.

Solid State NMR a Powerful Technique for Investigating Sustainable/Renewable Cellulose-Based Materials

Solid state nuclear magnetic resonance (ssNMR) is a powerful and attractive characterization method for obtaining insights into the chemical structure and dynamics of a wide range of materials. Current interest in cellulose-based materials, as sustainable and renewable natural polymer products, requires deep investigation and analysis of the chemical structure, molecular packing, end chain motion, functional modification, and solvent–matrix interactions, which strongly dictate the final product properties and tailor their end applications. In comparison to other spectroscopic techniques, on an atomic level, ssNMR is considered more advanced, especially in the structural analysis of cellulose-based materials; however, due to a dearth in the availability of a broad range of pulse sequences, and time consuming experiments, its capabilities are underestimated. This critical review article presents the comprehensive and up-to-date work done using ssNMR, including the most advanced NMR strategies used to overcome and resolve the structural difficulties present in different types of cellulose-based materials.

Application of Raw and Chemically Modified Biomasses for Heterogeneous Cu-Catalysed Conversion of Aryl boronic Acids to Phenols Derivatives

This work describes the application of raw and chemically modified cellulose and sugarcane bagasse for ipso-hydroxylation of aryl boronic acids in environmentally friendly reaction conditions. The catalytic efficiency of five support-[Cu] materials was compared in forming phenols from aryl boronic acids. Our investigation highlights that the CEDA-[Cu] material (6-deoxy-6-aminoethyleneamino cellulose loaded with Cu) leads to the best results under very mild reaction conditions. The optimized catalytic sequence, allowing a facile transformation of boronic acids to phenols, required the mandatory and joint presence of the support, Cu2O, and KOH at room temperature. CEDA-[Cu] was characterized using 13C solid-state NMR, ICP, and FTIR. The use of CEDA-[Cu] accounts for the efficacious synthesis of variously substituted phenol derivatives and presents very good recyclability after five catalytic cycles.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

Extracellular matrixes (ECMs), such as the cell walls and biofilms, are important for supporting cell integrity and function and regulating intercellular communication. These biomaterials are also of significant interest to the production of biofuels and the development of antimicrobial treatment. Solid-state nuclear magnetic resonance (ssNMR) and magic-angle spinning-dynamic nuclear polarization (MAS-DNP) are uniquely powerful for understanding the conformational structure, dynamical characteristics, and supramolecular assemblies of carbohydrates and other biomolecules in ECMs. This review highlights the recent high-resolution investigations of intact ECMs and native cells in many organisms spanning across plants, bacteria, fungi, and algae. We spotlight the structural principles identified in ECMs, discuss the current technical limitation and underexplored biochemical topics, and point out the promising opportunities enabled by the recent advances of the rapidly evolving ssNMR technology.

Theoretical study of cellulose II nanocrystals with different exposed facets

Derived from the most abundant natural polymer, cellulose nanocrystal materials have attracted attention in recent decades due to their chemical and mechanical properties. However, still unclear is the influence of different exposed facets of the cellulose nanocrystals on the physicochemical properties. Herein, we first designed cellulose II nanocrystals with different exposed facets, the hydroxymethyl conformations distribution, hydrogen bond (HB) analysis, as well as the relative structural stability of these models (including crystal facets {A, B, O} and Type-A models vary in size) are theoretically investigated. The results reveal that the HB network of terminal anhydroglucose depends on the adjacent chain's contact sites in nanocrystals exposed with different facets. Compared to nanocrystals exposed with inclined facet, these exposed with flat facet tend to be the most stable. Therefore, the strategy of tuning exposed crystal facets will guide the design of novel cellulose nanocrystals with various physicochemical properties.

NMR study on the cellulose dissolution mechanism in CaCl2·6H2O-LiCl molten salt hydrate

As there is a rising interest in upgrading cellulose to high-performance bio-products, the studies on innovative reaction media and processes have been leaping forward. Green solvents in terms of cellulose dissolution and brief processes for upgrading are critical to green chemistry. However, most solvent systems generally exhibit defects in harsh pH operating windows with limited temperature ranges, environmental pollution, long reaction times, complicated processes, etc. In this work, we have provided a novel molten salt hydrate (CaCl₂·6H₂O-LiCl) as a green solvent and investigated the role of hydrated molten salts in the dissolution process via the solid state nuclear magnetic resonance (NMR) technique. The cellulose could be dissolved in CaCl₂·6H₂O-LiCl molten salt hydrated at 120 °C with 3.0% solubility and regenerated in-situ by cooling down to ambient temperature. The regenerated cellulose exhibited a high solubility and excellent stability. From ⁷Li single pulse NMR experiments, it was observed that two types of Li⁺ existed in the cellulose dissolution, and the Li⁺ significantly impacted the dissolving process and the dissolution ability of cellulose. This work would provide an environmental-friendly strategy to prepare cellulose solutions for biocompatible cellulose materials.

A facile method for the phosphorylation of cellulosic fabric via atmospheric pressure plasma

Green chemistry approach for phosphorylation of cellulose, under atmospheric pressure plasma was investigated and compared with conventional thermal method. The attachment of the phosphate groups was evaluated by ³¹P and ¹³C solid state NMR spectroscopy and XPS. The thermal method led to the formation of monophosphate of cellulose along with a side product of polymerized phosphate, whereas the plasma method produced only the monophosphate, without any side products. Unlike with the thermal treatment, the appearance and the mechanical properties of the viscose fabric remained nearly same after the plasma treatment. Also, the dyeability of the plasma modified fabric remained unchanged, whereas it decreased significantly in the thermally modified fabric. The amount of phosphate quantified by phosphomolybdate assay was found to be 2.88 ± 0.06 and 4.09 ± 0.19 % in the plasma and the thermal methods, respectively. This method has the potential to replace the existing methods of phosphorylation of cellulose.

Bottom-up Construction of Xylan Nanocrystals in Dimethyl Sulfoxide

A new type of polysaccharide (hemicellulose) nanocrystal, bearing the shape of an anisotropic nanoflake, emerged from a dimethyl sulfoxide (DMSO) dispersion of wood-based xylan through heat-induced crystallization. The dimensions of these xylan nanocrystals were controlled by the crystallization conditions. Sharp signals in solid-state NMR indicated a well-ordered crystal structure. The unit cell is constituted of two asymmetric xylose residues, and DMSO molecules resided in a host-guest type of arrangement with more than one local environment. This corroborates with the identical ¹H NMR relaxation time between DMSO and xylan, indicative of intimate mixing of the two at the tens of nanometer length scale. X-ray and electron diffraction indicated a 2-fold helical helix along the chain in a monoclinic unit cell with an antiparallel arrangement, with chains placed on the 2-fold helix axes: at the corner and at the center. The 2-fold helical structure is unique for xylan for which only a 3-fold helical form has been reported. The DMSO molecules participated in the crystallization, and they were shown to be vital in stabilizing the crystalline structure. The manipulation of temperature, concentration, and incubation time of the xylan/DMSO dispersion provided pathways for the crystallization to form size-adjustable nanocrystals. As 20-30% of biomass consists of hemicelluloses, this work will serve as a starting point to understand the controlled assembly of hemicelluloses to discover their full application potential.

Microfibrillated cellulose from Argania spinosa shells as sustainable solid particles for O/W Pickering emulsions

Microfibrillated cellulose (MFC) from Argan (Argania spinosa) shells was prepared by chemical purification of cellulose, then mechanical disintegration via high pressure homogenization was performed to isolate fibrils of cellulose. Chemical characterization of raw argan shell (AS-R), purified cellulose (AS-C), and argan shell MFC (AS-MFC) included FT-IR, XRD and NMR. Morphological characterization of AS-MFC was assessed using TEM. Next, the use of AS-MFC as oil-in-water (O/W) emulsions stabilizer was investigated. The particle concentration was observed to affect the long-term stability of the emulsions; high concentrations (0.5-1 % w/w) of AS-MFC resulted in emulsions that were thermodynamically stable during 15 days of storage, which was demonstrated by the droplet's size evolution. The suitable oil concentration for a maximum volume of emulsion using 1 % w/w AS-MFC was demonstrated. The results show that AS-MFC is able to stabilize 70 % w/w MCT oil without visual phase separation. Finally, CLSM shows the adsorption of AS-MFC at the oil-water interface and the formation of a 3D network surrounding oil droplets, confirming Pickering emulsion formation and stabilization.

Conversion of Biomasses and Copper into Catalysts for Photocatalytic CO2 Reduction

The rapid increase of CO₂ in the atmosphere has caused serious environmental problems. Burning of biomass wastes increases the content of CO₂ in the environment. Herein, we propose a new strategy to convert biomass into photocatalysts for artificial CO₂ reduction. Using a hydrothermal method, carbohydrates from biomass can be converted into hydrothermal carbonaceous carbon (HTCC). The HTCC consists of plenty of sp²-hybridized structures, which are capable of absorbing solar light for photocatalytic CO₂ reduction. Furthermore, with the addition of Cu cocatalysts, higher activity can be obtained for CO₂ reduction. The activity of Cu-HTCC is 32 and 1.7 times higher than that of commercial TiO₂ and pure HTCC, respectively. This method provides a new strategy of trash to treasure, which converts biomass waste into photocatalysts for CO₂ reduction.

Recent studies on modified cellulose/nanocellulose epoxy composites: A systematic review

Cellulose and its derivatives are widely explored for films and thickening of pharmaceutical solutions, in paints, as reinforcement in composites, among others. This versatility is due to advantages such as renewability, low cost, and environmental friendliness. When used in polymer composites, due to the hydrophilic character of the cellulose, surface chemical modification is highly recommended to improve its compatibility with the polymeric matrix. Hence, this paper presents a systematic review of chemically modified cellulose/epoxy resin composites focusing on the last five years. The investigation followed the PRISMA protocol that delivers a meticulous summary of all available primary research in response to a research question. After including/excluding steps, thirty-six studies were included in the review. The results were presented focusing on thermal, mechanical and dynamic-mechanical properties of the composites. In brief, this methodology helped identifying the main gaps in knowledge in that field.

Solid state nuclear magnetic resonance studies of hydroxypropylmethylcellulose acetyl succinate polymer, a useful carrier in pharmaceutical solid dispersions

Hydroxypropylmethylcellulose (HPMC) acetyl succinate (HPMC-AS) is a key polymer used for the enablement of amorphous solid dispersions (ASDs) in oral solid dosage forms. Choice of the appropriate grade within the material is often made empirically by the manufacturer of small-scale formulations, followed by extensive real time stability. A key factor in understanding and predicting the performance of an ASD is related to the presence of hydrogen (or other) bonds between the polymer and active pharmaceutical ingredient (API), which will increase stability over the parameters captured by miscibility and predicted by the Gordon-Taylor equation. Solid state nuclear magnetic resonance (NMR) is particularly well equipped to probe spatial proximities, for example, between polymer and API; however, in the case of HPMC-AS, these interactions have been sometimes difficult to identity as the carbon-13 NMR spectra assignment is yet to be firmly established. Using feedstock, selectively substituted HPMC polymers, and NMR editing experiments, we propose here a comprehensive understanding of the chemical structure of HPMC-AS and a definitive spectral assignment of the ¹³ C NMR spectra of this polymer. The NMR data also capture the molar ratios of the acetate and succinate moieties present in HPMC-AS of various grades without the need for post treatment required by chromatography methods commonly use in pharmacopoeia. This knowledge will allow the prediction and measurement of interactions between polymers and APIs and therefore a rational choice of polymer grade to enhance the solid state stability of ASDs.

Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM, PTssNMR and DWS

Cellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 °C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.

Coagulation using organic carbonates opens up a sustainable route towards regenerated cellulose films

Due to their biodegradability, biocompatibility and sustainable nature, regenerated cellulose (RC) films are of enormous relevance for green applications including medicinal, environmental and separation technologies. However, the processes used so far are very hazardous to the environment and health. Here, we disclose a simple, fast, environmentally friendly, nontoxic and cost-effective processing method for preparing RC films. High quality non-transparent and transparent RC films and powders can be produced by dissolution with tetrabutylphosphonium hydroxide [TBPH]/[TBP]⁺[OH]^- followed by coagulation with organic carbonates. Investigations on the coagulation mechanism revealed an extremely fast reaction between the carbonates and the hydroxide ions. The high-quality powders and films were fully characterized with respect to structure, surface morphology, permeation and selectivity. This method represents a future-oriented green alternative to known industrial processes.

Purification, Preliminary Structural Characterization, and In Vitro Inhibitory Effect on Digestive Enzymes by β-Glucan from Qingke (Tibetan Hulless Barley)

Background and Objective. Qingke (Tibetan hulless barley, Hordeum vulgare L.) contains a high content of β-glucan among all the cereal varieties. Although β-glucan has multiple physiological functions, the physiological function of qingke β-glucan was few studied. In this study, the β-glucan was isolated, purified, determined the structural characterization, and measured the inhibitory activity to enzymes correlating blood sugar and lipid. Methods. β-Glucan was isolated from enzymatic aqueous extract of qingke by using deproteinization, decolorization, DEAE-52 column chromatography, and sepharose CL-4B agarose gel column chromatography. The structure of the β-glucan was determined using FT-IR and 13C-NMR spectra analysis, and molecular mass by use of HPSEC-dRI-LS. The kinematic viscosity was measured. The inhibitory effects of this β-glucan on four enzymes were investigated. Results. This β-glucan had a uniform molecular weight of 201,000 Da with β-(1⟶4) as the main chain and β-(1⟶3) as a side chain. The β-glucan presented a relatively strong inhibitory activity on α-glucosidase, moderate inhibition on invertase, and a weak inhibition on α-amylase, whereas it did not inhibit lipase. Conclusion. The study indicates that the enzymatic β-glucan from qingke has the potential as natural auxiliary hypoglycemic additives in functional medicine or foods.

Green Gas-Mediated Cross-Linking Generates Biomolecular Hydrogels with Enhanced Strength and Excellent Hemostasis for Wound Healing

Forming biomolecular hydrogels with a combination of high strength and biocompatibility is still a challenge. Herein, we demonstrated a green gas (CO₂)-mediated chemical cross-linking strategy that can produce a double-network cellulose/silk fibroin hydrogel (CSH) with significantly elevated mechanical strength while bypassing the toxicity of routine cross-linking agents. Specifically, cellulose and silk fibroin (SF) were first covalently cross-linked in NaOH/urea solution to create the primary network. Then, CO₂ gas was introduced into the resultant CSH precursor gels to form carbonates to reduce the pH value of the intra-hydrogel environment from basic to neutral conditions. The pH reduction induced the ordered aggregation of cellulose chains and concomitant hydrogen bonding between these chains, leading to the formation of hydrogels with significantly improved mechanical strength. The CSHs could promote the adhesion and proliferation of the mouse fibroblast cell line (L929), and the CSHs proved to be of low hemolysis and could accelerate blood clotting and decrease blood loss. The CSHs with SF content of 1 wt % healed the wound in vivo within only 12 days through the acceleration of re-epithelialization and revascularization. Consequently, our current work not only reported a feasible alternative for wound dressings but also provided a new green gas-mediated cross-linking strategy for generating mechanically strong, hemostatic, and biocompatible hydrogels.

Enhanced phosphate removal using zirconium hydroxide encapsulated in quaternized cellulose

Zirconium-based materials are efficient adsorbent for aqueous phosphate removal. However, current zirconium-based materials still show unsatisfied performance on adsorption capacity and selectivity. Here, we demonstrate a zirconium hydroxide encapsulated in quaternized cellulose (QC-Zr) for the selective phosphate removal. Zirconium hydroxide nanoparticles were simultaneously generated in situ with the QC framework and firmly anchored in the three-dimensional (3D) cross-linked cellulose chains. The maximum P adsorption capacity of QC-Zr was 83.6 mg P/g. Furthermore, the QC-Zr shows high P adsorption performance in a wide pH range, generally due to the electrostatic effects of quaternized cellulose. The enhanced adsorption of P was also achieved in the presence of competing anions (including Cl^-, NO₃^-, SO₄^2-, SO₄^4-) and humic acid (HA) even at a molar ratio up to 20 levels. The column adsorption capacity of QC-Zr reached 4000 bed volumes (BV) at EBCT = 0.5 min as the P concentration decreased from 2.5 to 0.5 mg/L. Mechanism study revealed that both -N⁺(CH₃)₃ groups and zirconium hydroxide were involved in phosphate adsorption via electrostatic interactions between -N⁺(CH₃)₃ and phosphate, and the formation of zirconium hydrogen phosphate (Zr(HPO₄)x). The ³¹P nuclear magnetic resonance (NMR) study implied that P surface-precipitated and inner-sphere complexed with zirconium hydroxide at a ratio of 3:1.

TV, Huamani-Palomino RG, Baena-Moncada AM. Simultaneous adsorption of a ternary mixture of brilliant green, rhodamine B and methyl orange as artificial wastewater onto biochar from cocoa pod husk waste. Quantification of dyes using the derivative spectrophotometry method

Biochar obtained from cocoa pod husk waste for the simultaneous adsorption of a ternary mixture of brilliant green, rhodamine B and methyl orange.

Investigation of the internal structure and dynamics of cellulose by 13C-NMR relaxometry and 2DPASS-MAS-NMR measurements

Internal structure and dynamics of commercial and natural cellulose were studied by measuring chemical shift anisotropy (CSA) parameters, and spin-lattice relaxation rate (1/T₁) at each and every chemically different carbon nuclear site. CSA parameters were measured by ¹³C two-dimensional phase adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) NMR experiment. Site specific spin-lattice relaxation time was measured by Torchia-CP method. Anisotropy parameters of C4 and C6 regions are higher than C1 and C235 regions and asymmetry of C4 line is lower than any other carbon site. The higher values of CSA parameters of C4 and C6 nuclei arise due to the rotation of O4-C4, C1-O4, O5-C5-C6-O6 and C4-C5-C6-O6 bonds at torsion angles ψ, Φ, χ and χ' respectively and the influence of interchain and intrachain hydrogen bondings. Two distinct peaks are also observed for C4 and C6 resonance line position-one peak arises primarily due to the nuclei in amorphous region and another one arises due to the same nuclei resides in paracrystalline region. The spin-lattice relaxation time and the CSA parameters are different at these two distinct peak positions of C4 and C6 line. Molecular correlation time of each and every chemically different carbon site was calculated with the help of CSA parameters and spin-lattice relaxation time. The molecular correlation time of the amorphous region is one order of magnitude less than the crystalline region. The distinction between amorphous and paracrystalline regions of cellulose is more vividly portrayed by determining spin-lattice relaxation time, CSA parameters, and molecular correlation time at each and every chemically different carbon site. This type of study correlating the structure and dynamics of cellulose will illuminate the path of inventing biomimetic materials.

Designing of a Phosphorus, Nitrogen, and Sulfur Three-Flame Retardant Applied in a Gel Poly-m-phenyleneisophthalamide Nanofiber Membrane for Advanced Safety Lithium-Sulfur Batteries

Based on the urgent demand of non-flammable electrospun nanofiber separators and the strong adsorption to polysulfides through chemical doping in separators for Li-S cell, in this study, a phosphorus, nitrogen, and sulfur three-flame retardant (di-(2-(5,5-dimethyl-2-sulfido-1,3,2-dioxaphosphinan-2-yl)hydrazineyl)-P-ethylphosphinic) was synthesized and a high-performance flame-retarding poly-m-phenyleneisophthalamide (PMIA) membrane was successfully prepared through blend electrospinning with the flame retardant, it is regarded as a promising gel nanofiber membrane with advanced safety for the lithium-sulfur (Li-S) cell, and it was systematically explored and analyzed. It was presented that the modified PMIA electrospun membrane with the synthesized flame retardant possessed excellent flame retardation, outstanding thermal stability, and good mechanical strength. Meanwhile, the prepared membrane showed extraordinarily high uptake and preserving retention of the liquid electrolyte and enhanced ionic conductivity. More importantly, the assembled Li-S cells using the obtained membrane exhibited excellent cycling retention and outstanding rate capability because of its fast ion transportation and good interfacial compatibility. The assembled batteries with the novel membrane exhibited a high first-cycle discharge capacity of 1121.50 mA h g^-1, superior discharge capacity retention of 713.41 mA h g^-1, and high Coulombic efficiency of 98.46% after 600 cycles at the 0.5 C rate. In addition, the limiting oxygen index of the obtained nanofiber membrane with flame retardancy was as high as ∼30.0%, which could greatly enhance the safety of the electrospun nanofiber separator. The excellent electrochemical performances and safety for the battery assembled with the prepared gel PMIA nanofiber membrane were attributed to the significantly prevented "shuttle effect" of lithium polysulfides based on the physical capturing of lithium polysulfides through the obtained jelly-like gel state and chemical binding of polysulfide intermediates through the tridoped phosphorus, nitrogen, and sulfur elements in the PMIA and the flame retardant. All of these excellent properties will promote the great development of the Li-S battery with high performance and satisfactory safety.

Set-Up of Bacterial Cellulose Production From the Genus Komagataeibacter and Its Use in a Gluten-Free Bakery Product as a Case Study

The use of bacterial cellulose (BC) in food systems is still limited due to production costs. Nine clones belonging to Komagataeibacter hansenii, Komagataeibacter nataicola, Komagataeibacter rhaeticus, Komagataeibacter swingsii, and Komagataeibacter xylinus species were screened for cellulose productivity in growth tests with five different carbon sources and three nitrogen sources. The water-holding and rehydration capacities of the purified cellulose were determined. The structure of the polymer was investigated through nuclear magnetic resonance (NMR) spectroscopy, attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy and X-ray diffraction (XRD) analysis, and observed by scanning electron microscope (SEM). Natural mutants of K. rhaeticus LMG 22126T and K. swingsii LMG 22125T showed different productivity. The factors "bacterial isolate" and "nitrogen source" significantly affected the production of cellulose (p < 0.01) rather than the factor "carbon source" (p = 0.15). However, on average, the best conditions for increasing yield were found in medium containing glucose and peptone. Water-holding capacity (WHC) values ranged from 10.7 to 42.3 (g water/g cellulose) with significant differences among strains (p < 0.01), while the rehydration capacity varied from 4.2 to 9.3 (g water/g cellulose). A high crystallinity (64-80%) was detected in all samples with Iα fractions corresponding to 67-93%. The ATR-FT-IR spectra and the XRD patterns confirmed the expected structure. BC made by GVP isolate of K. rhaeticus LMG 22126T, which was the strain with the highest yield, was added to a gluten-free bread formulation. Results obtained from measurements of technological parameters in dough leavening and baking trials were promising for implementation in potential novel foods.

Unambiguous Ex Situ and in Cell 2D 13C Solid-State NMR Characterization of Starch and Its Constituents

Starch is the most abundant energy storage molecule in plants and is an essential part of the human diet. This glucose polymer is composed of amorphous and crystalline domains in different forms (A and B types) with specific physicochemical properties that determine its bioavailability for an organism, as well as its value in the food industry. Using two-dimensional (2D) high resolution solid-state nuclear magnetic resonance (SS-NMR) on 13C-labelled starches that were obtained from Chlamydomonas reinhardtii microalgae, we established a complete and unambiguous assignment for starch and its constituents (amylopectin and amylose) in the two crystalline forms and in the amorphous state. We also assigned so far unreported non-reducing end groups and assessed starch chain length, crystallinity and amylose content. Starch was then characterized in situ, i.e., by 13C solid-state NMR of intact microalgal cells. Our in-cell methodology also enabled the identification of the effect of nitrogen starvation on starch metabolism. This work shows how solid-state NMR can enable the identification of starch structure, chemical modifications and biosynthesis in situ in intact microorganisms, eliminating time consuming and potentially altering purification steps.

Preparation and Characterization of Regenerated Cellulose Film from a Solution in Lithium Bromide Molten Salt Hydrate

In this study, the molten salt hydrate of lithium bromide (LiBr) was utilized as a non-derivatizing cellulose dissolution solvent to prepare regenerated cellulose films for kraft pulp. The effects of LiBr concentrations (60, 62, and 65 wt %) and dissolving time (from 5 to 40 min with the interval of 5 min) on the structures and the properties of the films were investigated. Fourier transform infrared (FT-IR) and cross-polarization magic-angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) characterizations verified the breakage of inter- and intra-cellulose hydrogen bonds during the regeneration, resulting in the disruption of the crystalline structure of cellulose. X-ray diffraction (XRD) data indicated that the regeneration converted the polymorphism of cellulose from I to II as well as decreased its crystallinity. Ultraviolet-visible spectra (UV-Vis) and scanning electron microscopy (SEM) analyses revealed the excellent optical transparency of the films to visible light due to the complete dissolution of cellulose fibers as well as the sufficient breaking of the inter- and intra-cellulose hydrogen bonds. In terms of tensile testing, tuning LiBr concentrations and dissolving time could increase the elongation at break and tensile strength of the films. The maximum elongation at break of 26% and tensile strength of 67 MPa were achieved when the films prepared in 65 wt % LiBr for 10 and 15 min, respectively. These results indicated the great potential of the cellulose films for packaging use.

A new approach for bioethanol production from sugarcane bagasse using hydrodynamic cavitation assisted-pretreatment and column reactors

Hydrodynamic cavitation (HC) was adopted to assist alkaline-hydrogen peroxide pretreatment of sugarcane bagasse (SCB). In the following condition: 0.29 M of NaOH, 0.78% (v/v) of H₂O₂, 9.95 min of process time and 3 bar of inlet pressure, 95.4% of digestibility of cellulosic fraction was achieved. To take the best use of the pretreated biomass, the overall process was intensified by way of employing a packed bed flow-through column reactor and thus enabling to handle a high solid loading of 20%, thereby leading to cellulose and hemicellulose conversions to 74.7% and 75%, respectively. In the fermentation step, a bubble column reactor was introduced to maximize ethanol production from the pretreated SCB by Scheffersomyces stipitis NRRL-Y7124, resulting in 31.50 g/L of ethanol, 0.49 g/g of ethanol yield and 0.68 g/L.h of productivity. All this showed that our HC-assisted NaOH-H₂O₂ pretreatment strategy along with the process intensification approach might offer an option for SCB-based biorefineries.