NMR characterization of cellulose acetate: Mole fraction of monomers in cellulose acetate determined from carbonyl carbon resonances

Cellulose, cellulose nanofibers, and cellulose acetate from Butia fruits (Butia odorata): Chemical, morphological, structural, and thermal properties

Cellulose possesses numerous advantageous properties and is a precursor to compounds and derivatives. The objective of this study was to isolate and characterize cellulose from Butia fruits and simultaneously produce cellulose nanofibers and cellulose acetate from the isolated cellulose. Cellulose extraction was performed using a combination of alkaline and bleaching treatments, while the production of cellulose nanofibers and cellulose acetate was achieved through acid hydrolysis and acetylation, respectively. The materials were characterized by their chemical composition, size distribution, zeta potential, morphology, relative crystallinity (XRD), functional groups (FTIR), molecular structure (NMR), and thermal stability (TGA). The Butia crude fibers presented 49.4 % cellulose, 4.5 % hemicellulose, 25.4 % lignin, and 1.3 % ash. The cellulose nanofibers presented an average diameter ranging from 13.7 to 93.1 nm and exhibited a high degree of crystallinity (63.3 %). FTIR, XRD, 13C, and 1H NMR analyses confirmed that the isolation processes effectively removed amorphous regions from the cellulose nanofibers and confirmed the cellulose acetylation process. As demonstrated, cellulosic materials derived from Butia fruit exhibit promise for various applications, including their potential use as reinforcing agents in polymer matrices, due to their high extraction yield, thermal properties, and crystallinity.

Structural Characterization of 6-Halo-6-Deoxycelluloses by Direct-Dissolution Solution-State NMR Spectroscopy

Regioselective modifications of cellulose using activated cellulose derivatives such as 6-halo-6-deoxycelluloses provide a convenient approach for developing sustainable products with properties tailored to specific applications. However, maintaining precise regiochemical control of substituent distribution in 6-halo-6-deoxycelluloses is challenging due to their insolubility in most common solvents and the resulting difficulties in precise structure elucidation by modern instrumental analytical techniques. Herein, an accessible NMR-based approach toward detailed characterization of 6-halo-6-deoxycelluloses, including the determination of the degrees of substitution at carbon 6 (DS6), is presented. It is shown that the direct-dissolution cellulose solvent, tetrabutylphosphonium acetate:DMSO-d6, converts 6-halo-6-deoxycelluloses to 6-monoacetylcellulose, enabling in situ solution-state NMR measurements. A range of 1D and 2D NMR experiments is used to demonstrate the quantitivity of the conversion and provide optimum dissolution conditions. In comparison with other NMR-based derivatization protocols for elucidating the structure of 6-halo-6-deoxycelluloses, the presented approach offers major advantages in terms of accuracy, speed, and simplicity of analysis, and minimal requirements for reagents or NMR instrumentation.

Di-aldehyde tunicate cellulose nanocrystal (D-tCNC) aerogels for drug delivery: Effect of D-tCNC composition on aerogel structure and release properties

Aerogels as drug carriers have the characteristics of a large specific surface area, high porosity and an elastic skeleton structure. Compared with traditional drug carriers, the use of aerogels as drug carriers can avoid the complexity of drug delivery and improve the efficiency of drug loading. In this work, the oxidation of tunicate cellulose nanocrystals (tCNCs) with NaIO4 was used to prepare di-aldehyde tunicate cellulose nanocrystals (D-tCNCs). Tetracycline (TC) was used as a drug model and pH-responsive drug-loaded aerogels were prepared by the Schiff base reaction between TC and the aldehyde group on D-tCNCs. The chemical structure, crystallinity, morphology, compression properties, porosity, swelling rate and drug loading properties were investigated by FT-IR, XRD, SEM and universal testing machines. The results showed that the porosity and equilibrium swelling ratio of the D-tCNC-TC aerogels were 95.87 % and 17.52 g/g, respectively. The stress of the D-tCNC-TC aerogel at 15 % compression was 0.07 MPa. Moreover, the analysis of drug-loaded aerogels indicated that the drug loading and encapsulation rates of D-tCNC-TC aerogels were 16.86 % and 78.75 %, respectively. In in vitro release experiments, the cumulative release rate of drug-loaded aerogel at pH = 1.2 and pH = 7.4 was 87.5 % and 79.3 %, respectively. These results indicated that D-tCNC-TC aerogels have good drug loading capacity and are pH-responsive in the pH range of 1.2 to 7.4. The prepared D-tCNC-TC aerogels are expected to be applied in drug delivery systems.

Solution-state nuclear magnetic resonance spectroscopy of crystalline cellulosic materials using a direct dissolution ionic liquid electrolyte

Owing to its high sustainable production capacity, cellulose represents a valuable feedstock for the development of more sustainable alternatives to currently used fossil fuel-based materials. Chemical analysis of cellulose remains challenging, and analytical techniques have not advanced as fast as the development of the proposed materials science applications. Crystalline cellulosic materials are insoluble in most solvents, which restricts direct analytical techniques to lower-resolution solid-state spectroscopy, destructive indirect procedures or to 'old-school' derivatization protocols. While investigating their use for biomass valorization, tetralkylphosphonium ionic liquids (ILs) exhibited advantageous properties for direct solution-state nuclear magnetic resonance (NMR) analysis of crystalline cellulose. After screening and optimization, the IL tetra-n-butylphosphonium acetate [P₄₄₄₄][OAc], diluted with dimethyl sulfoxide-d₆, was found to be the most promising partly deuterated solvent system for high-resolution solution-state NMR. The solvent system has been used for the measurement of both 1D and 2D experiments for a wide substrate scope, with excellent spectral quality and signal-to-noise, all with modest collection times. The procedure initially describes the scalable syntheses of an IL, in 24-72 h, of sufficient purity, yielding a stock electrolyte solution. The dissolution of cellulosic materials and preparation of NMR samples is presented, with pretreatment, concentration and dissolution time recommendations for different sample types. Also included is a set of recommended 1D and 2D NMR experiments with parameters optimized for an in-depth structural characterization of cellulosic materials. The time required for full characterization varies between a few hours and several days.

Polyurethane films formation from microcrystalline cellulose as a polyol and cellulose nanocrystals as additive: Reactions favored by the low viscosity of the source of isocyanate groups used

To simultaneously form films while synthesizing solvent-free and catalyst-free bio-based polyurethanes, hexamethylene diisocyanate trimer was selected as an isocyanate group source to produce a low-viscosity reaction medium for dispersing high contents of microcrystalline cellulose (MCC, polyol) and cellulose nanocrystals (CNC). Castor oil was used as an additional polyol source. Up to 80 % of the MCC was dispersed, producing a film exhibiting the highest T_g (72 °C), tensile strength (18 MPa), and Young's modulus (522.4 MPa). 12.5 % (30 % MCC) and 7.5 % (50 % MCC) of CNC dispersed in the reaction medium formed films stiffer than their counterparts. All the films exhibited transparency and high crystallinity. The contact angle/zeta potential (ζ) indicated hydrophobic film surfaces. At pH 7.4, ζ suggested that the films interacted with physiological fluids favorably. The films were non-cytotoxic, and the composites exhibited cell growth compared with the control. The reported results, as far as it is known, are unprecedented.

Spatioselective surface chemistry for the production of functional and chemically anisotropic nanocellulose colloids

Maximizing the benefits of nanomaterials from biomass requires unique considerations associated with their native chemical and physical structure. Both cellulose nanofibrils and nanocrystals are extracted from cellulose fibers via a top-down approach and have significantly advanced materials chemistry and set new benchmarks in the last decade. One major challenge has been to prepare defined and selectively modified nanocelluloses, which would, e.g., allow optimal particle interactions and thereby further improve the properties of processed materials. At the molecular and crystallite level, the surface of nanocelluloses offers an alternating chemical structure and functional groups of different reactivity, enabling straightforward avenues towards chemically anisotropic and molecularly patterned nanoparticles via spatioselective chemical modification. In this review, we will explain the influence and role of the multiscale hierarchy of cellulose fibers in chemical modifications, and critically discuss recent advances in selective surface chemistry of nanocelluloses. Finally, we will demonstrate the potential of those chemically anisotropic nanocelluloses in materials science and discuss challenges and opportunities in this field.

A zwitterionic polymer-inspired material mediated efficient CRISPR-Cas9 gene editing

The type II prokaryotic CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR/Cas9) adaptive immune system is a cutting-edge genome-editing toolbox. However, its applications are still limited by its inefficient transduction. Herein, we present a novel gene vector, the zwitterionic polymer-inspired material with branched structure (ZEBRA) for efficient CRISPR/Cas9 delivery. Polo-like kinase 1 (PLK1) acts as a master regulator of mitosis and overexpresses in multiple tumor cells. The Cas9 and single guide sgRNA (sgRNA)-encoded plasmid was transduced to knockout Plk1 gene, which was expected to inhibit the expression of PLK1. Our studies demonstrated that ZEBRA enabled to transduce the CRISPR/Cas9 system with large size into the cells efficiently. The transduction with ZEBRA was cell line dependent, which showed ∼10-fold higher in CD44-positive cancer cell lines compared with CD44-negative ones. Furthermore, ZEBRA induced high-level expression of Cas9 proteins by the delivery of CRISPR/Cas9 and efficient gene editing of Plk1 gene, and inhibited the tumor cell growth significantly. This zwitterionic polymer-inspired material is an effective and targeted gene delivery vector and further studies are required to explore its potential in gene delivery applications.

Solvent-free production of thermoplastic lignocellulose from wood pulp by reactive extrusion

A novel acylation approach suited to rapid bulk thermoplasticization of lignocellulose without solvents was previously demonstrated by the authors in benchtop batch studies. The method relies upon a benzethonium chloride/sulfuric acid functionalizing agent at low concentrations to act as a wetting agent for the wood pulp, similar to an ionic liquid, yet binds to the lignocellulose ester as a flow aid in the final thermoplastic. The present investigation evaluates the approach in a residence time-limited (45-90 s) continuous twin-screw reactor, where intensive mixing and heat were found to yield high acylation. The modified lignocellulose exhibited desired thermoplasticity by being melt moldable without the need for plasticizers and maintained much of the excellent stiffness of cellulose, demonstrating a maximum flexural modulus of 5.4 GPa and tensile modulus of 1.8 GPa. The influence of extrusion conditions on thermoplasticity was examined by a Design of Experiments (DOE) analysis.

CO2-assisted catalytic pyrolysis of cellulose acetate using Ni-based catalysts

Cellulose acetate (CA) is one of widely used polymers for chemical and medical applications due to its versatile physico-chemical functionalities. Although its recycle is available after a deacetylation process, the recycle process releases a huge amount of wastewater. Thus, this study investigated a direct disposal process of CA with its valorization to syngas (H₂ and CO) through pyrolysis. To construct more environmentally benign process, CO₂ was used as a co-feedstock with CA to simultaneously convert them into syngas. Pyrolysis of CA in N₂ was performed as a reference study to examine the effectiveness of CO₂ on valorization of CA. Acetic acid and methyl acetate were main volatile pyrolysates (VPs) from CA pyrolysis, and the further thermal cracking of VPs resulted in syngas and CH₄ formations under both N₂ and CO₂ conditions. To expedite syngas formations, multi-stage pyrolysis (two-stage pyrolysis) and catalytic pyrolysis were employed. With the increased thermal energy through two-stage pyrolysis, four times more production of syngas was shown, comparing to the result of a single-stage pyrolysis. With Ni catalysts, the syngas formation was the two orders of magnitude higher than the single-stage pyrolysis, and the significant enhancement of CO formation was shown in the presence of CO₂ due to combined effects of CO₂ and the Ni-based catalysts. This CO enhancement resulted from catalytically expedited gas phase reactions between CO₂ and VPs evolved from CA. In addition, the CO₂ contributed to the suppression of coke deposition on the catalyst, thereby suggesting more technical and environmental benefits of CO₂ as a reactive co-feedstock of pyrolysis in reference to N₂. Therefore, this study proved the direct and versatile technical platform to convert CA and CO₂ into syngas.

Substituent distribution of propyl cellulose studied by nuclear magnetic resonance

A series of propyl cellulose (PC) samples with different degrees of substitution (DS) ranging from 0.34 to 2.02 were prepared by a slurry method using propyl bromide as the etherification reagent. Two-dimensional nuclear magnetic resonance (NMR) studies were performed to identify the ¹H and ¹³C chemical shifts of eight anhydroglucose units (AGUs) in PC chains including un-, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted ones. In addition, the mole fractions (χ) of these AGUs in the studied PC samples and their changes with DS were determined from the quantitative ¹³C NMR spectra. The obtained χ-DS profiles were different from those of methyl and ethyl celluloses prepared by a similar slurry method, indicating that the molecular sizes of the substituent reagents utilized for cellulose ethers strongly affected their substituent distributions.

DFT study of the influence of acetyl groups of cellulose acetate on its intrinsic birefringence and wavelength dependence

The effect of the acetyl groups of cellulose acetate (CA) on its intrinsic birefringence and its wavelength dependence was investigated using density functional theory (DFT). Seven types of CA repeating-unit models that differ in their degree of substitution (DS) and substitution sites were used in the calculations. The results suggested that the intrinsic birefringence (Δn°) and its wavelength dependence significantly depended on the conformations of the acetyl group at C6. Additionally, the intrinsic birefringence of CA films was estimated as the ensemble average of the calculated Δn° values of the conformers. The increase in the DS of CA led to a more negative intrinsic birefringence and a larger wavelength dependence. The computational results were in good qualitative agreement with the experimental results and suggested that conformational variety and/or its control would be important factors for the design of optical films containing CA.

Two-dimensional NMR data of a series of methylcellulose with different degrees of substitution

This article contains two-dimensional (2D) NMR experimental data for a series of methylcellulose (MC) with different substitution degrees (DS), obtained by the Bruker BioSpin 500 MHz NMR spectrometer (Germany). The data facilitated the ¹H and ¹³C chemical shifts of eight anhydroglucose units (AGUs) comprising MC chains-unsubstituted, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted AGUs. Data include analyzed the 2D NMR spectra of the MC samples, which are related to the subject of an article in Carbohydrate Polymers, entitled "NMR characterization of methylcellulose: Chemical shift assignment and mole fraction of monomers in the polymer chains" (Kon et al., 2017) [1]. These data can be very helpful to assign the ¹H and ¹³C chemical shifts of the other cellulose derivatives, especially cellulose ethers.