Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and deacetylation of ultrafine cellulose acetate fibers

Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004     

Effect of Molecular Structure on the GasPermeability of Cellulose Aliphatate Esters简

In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.     

Novel cellulose esters derived from the levopimaric acid-maleic anhydride adduct: synthesis,characterization, and properties

Synthesis of maleated pimaric acid (MPA) cellulose esters is first reported in this work. Cellulose esterification was performed by reacting microcrystalline cellulose with monoacid chloride of MPA (MPA-Cl) in presence of pyridine as catalyst and reaction medium. The syntheses were started in a heterogeneous solid–liquid reaction medium, but as the reaction advanced, the reaction mass turned into a homogeneous solution. The effects of MPA-Cl/anhydroglucose unit molar ratio, reaction temperature, and reaction duration on the yield and degree of substitution (DS) of cellulose esters (CEs) were investigated. CEs with DS ranging from 2.6 to 2.8 were achieved at molar ratios of 5.5–6.0 after 12–16 h at 118 °C. The purified products were characterized by elemental analysis, IR and ¹³C-NMR spectroscopy, and thermogravimetric analysis. CEs are soluble or partially soluble in usual organic solvents, depending on DS. Transparent films were prepared using CE-cyclohexanone solutions.     

Relationship between distribution of substituents and water solubility of O-methyl cellulose

The solubility behavior of O-methyl cellulose (MC) in water was investigated in terms of the distribution of substituents along the cellulose chain as well as in the anhydroglucose (AHG) units. For this purpose, three different types of MC samples were prepared by respective homogeneous reaction, i.e.. (i) methylation of cellulose acetate (CA) prepared from cellulose triacetate (CTA), followed by deacetylation, (ii) methylation of CA prepared by direct acetylation of cellulose in a 10% LiCl–dimethylacetamide (DMAc) solution, followed by deacetylation, and (iii) methylation of cellulose with dimethyl sulfate in a 10% LiCl–DMAc solution. Their water solubility was compared with that of MC samples prepared by the alkali cellulose process, i.e., by the heterogeneous reaction, including commercial products. It was found that water-soluble MC samples prepared by the alkali cellulose process exhibit a thermally-reversible sol-gel transition in aqueous solution, but all of the MC samples preapred homogeneous reactions show a normal phase separation in aqueous solution. This result gives a direct support for the consideration that the highly substituted glucose sequences present in the commercial MC act as “crosslinking loci” on warming. The distribution of substituents in the AHG units was estimated by ¹³C-NMR method. The results on the water solubility of MC were also discussed in terms of the distribution of substituents in the AHG units.     

6. Prospects for future applications of cellulose acetate

The prospects for future applications of cellulose acetate (CA) and cellulose esters (CE) were assessed via an analysis of literature data. An examination of more than 50,000 citations in the published literature with relevance to CA and CE has shown that, while the R&D effort continues without discernible slow-down, the emphasis has shifted in favor of D at the expense of R in recent years; more publications now originate in Southeast Asian countries; and most current journal articles deal with specialty products, such as membranes, controlled release agents, and biopolymers. The prospects for future applications are viewed as being related to the ability to add new performance features to CA, particularly thermal processability, water-dispersibility, and the ability to interact with other polymers on the molecular level. This can be achieved by such secondary modifications as the introduction of plasticizing (mixed) ester substituents, carboxyl groups, and the use of (monofunctional) oligomers in block copolymers, respectively. In addition, the adoption of acetylation technology to lower grade pulps and even wood and wood fibers may result in new business opportunities in thermoplastic and soluble wood esters, or in acetylated solid wood products with superior dimensional, biological and light-stability characteristics.     

Synthesis of cellulose benzoates under homogeneous conditions in an ionic liquid

The ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl) as a reaction medium was studied for the synthesis of cellulose benzoates by homogeneous acylation of dissolved cellulose with benzoyl chlorides in the absence of any catalysts. Cellulose benzoates with a degree of substitution (DS) in the range from about 1 to 3.0 were accessible under mild conditions. The DS of cellulose derivatives increased with the increase of the molar ratio of benzoyl chloride/anhydroglucose unit (AGU) in cellulose, reaction time, and reaction temperature. Benzoylation of cellulose with some 4-substituted benzoyl chlorides including 4-toluoyl chloride, 4-chlorobenzoyl chloride and 4-nitrobenzoyl chloride was also readily carried out under mild conditions. Furthermore, regioselectively substituted mixed cellulose esters were synthesized in this work. All products were characterized by means of FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. In addition, at the end of benzoylation of cellulose, the ionic liquid AmimCl was easily recycled. When the recycled AmimCl was used as the reaction media, the cellulose benzoate with a similar DS was obtained under comparable reaction conditions.     

Effect of humidity and solvent vapor phase on cellulose esters films

In the present study the effect of relative humidity (RH) during spin-coating process on the structural characteristics of cellulose acetate (CA), cellulose acetate phthalate (C-A-P), cellulose acetate butyrate (CAB) and carboxymethyl cellulose acetate butyrate (CMCAB) films was investigated by means of atomic force microscopy (AFM), ellipsometry and contact angle measurements. All polymer solutions were prepared in tetrahydrofuran (THF), which is a good solvent for all cellulose esters, and used for spin-coating at RH of (35 ± 5)%, (55 ± 5)% or (75 ± 5)%. The structural features were correlated with the molecular characteristics of each cellulose ester and with the balance between surface energies of water and THF and interface energy between water and THF. CA, CAB, CMCAB and C-A-P films spin-coated at RH of (55 ± 5)% were exposed to THF vapor during 3, 6, 9, 60 and 720 min. The structural changes on the cellulose esters films due to THF vapor exposition were monitored by means of AFM and ellipsometry. THF vapor enabled the mobility of cellulose esters chains, causing considerable changes in the film morphology. In the case of CA films, which are thermodynamically unstable, dewetting was observed after 6 min exposure to THF vapor. On the other hand, porous structures observed for C-A-P, CAB and CMCAB turned smooth and homogeneous after only 3 min exposure to THF vapor.     

Partial cellulose acetylation in 1-ethyl-3-methylimidazolium acetate induced by dichloromethane

Cellulose acetate (CA) is one on the most important cellulose derivatives. The use of ionic liquids in cellulose processing was recently discovered to not exclusively act as a solvent but also as a reagent. Recent studies showed that bulky chlorides as well as acetyl chloride mixed with ionic liquids can facilitate cellulose acetylation. This work focused on a simple chloro-organic cosolvent, dichloromethane (DCM), and showed the ability of this relatively small molecule, mixed with the ionic liquid, to facilitate homogenous acetylation by displacement of the acetate ion of the ionic liquid with a chloride ion. Maximal acetylation achieved by this method was a degree of substitution (DS) of 1.9, were only a small fraction of DCM was utilized for acetylation, well below even that expected for equimolar reaction. The degree of substitution was controlled by the dichloromethane content, thus controlling its solubility in water. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2458–2462     

Reactive dissolution of cellulose and pulp through acylation in pyridine

The direct acylation of cellulose and different pulps with various acid chlorides was systematically screened. The syntheses were started in a heterogeneous solid–liquid reaction medium in hot pyridine with aliphatic and aromatic acid chlorides. After a few hours, depending on the reagent used, a homogenous solution was obtained. The obtained cellulose esters usually show a high degree of substitution (DS) and polymerization and are soluble in organic solvents. Esterification of softwood dissolving pulp, hardwood kraft pulp and hardwood kraft pulp-hemicellulose poor were also studied. The results show that almost identical DS were obtained for pulp derivatives compared to esters of microcrystalline cellulose. Thermogravimetric analysis and differential scanning calorimetry of the synthesized materials showed an improved thermal stability and various discrete thermal transitions compared to the original cellulose. The scanning electron microscopy images of derivatives showed a relatively flat and smooth surface with an absence of fibrous structure. The reactive dissolution of cellulose or pulp in pyridine is a straightforward and easy route to obtain long-chain aliphatic and aromatic cellulose esters.     

Thermal behavior of cellulose acetate produced from homogeneous acetylation of bacterial cellulose

Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source.     

4.2 Chemical characteristics of cellulose acetate

The chemical structure of cellulose acetates (CA), different synthesis paths, analysis strategies and the correlation of these structural features with properties, especially with the solubility are summarized. Alternative paths, in particular homogeneous procedures, for the synthesis of CA are described focusing on the application of new media and the in situ activation of acetic acid. The preparation of selectively substituted CA is reviewed including the defined hydrolysis under acidic or basic conditions. Strategies for the structure analysis by means of ¹H- and ¹³C-NMR spectroscopy and by means of chromatographic methods are discussed. In addition, the preparation and the application of a variety of mixed CA ethers and esters are described.     

Water-soluble cellulose derivatives prepared by the action of solutions of nitrogen dioxide in dimethylformamide

Cellulose derivatives soluble in water and in dilute alkali were prepared by dissolving a bleached sulfite pulp in solutions of nitrogen dioxide in dimethylformamide (DMF) and heating at 70–90°C for 1–3 hr. No cellulose oxidation was detected. Nitrite esters and apparently also, nitrate esters, were formed with degrees of substitution (DS) ranging from 0.18 to 0.55 and with nitrogen contents ranging from 1.47 to 4.32%. Solution viscosities in water increased with increasing nitrogen content. The degree of polymerization (DP) decreased rapidly in the initial stages of the reaction followed by a slow, gradual decrease with increasing reaction times.     

Olefin metathesis applied to cellulose derivatives—Synthesis,analysis, and properties of new crosslinked cellulose plastic films

New crosslinked cellulose‐based plastic films were synthesized with olefin metathesis as a crosslinking reaction. Microcrystalline cellulose was first dissolved in a lithium chloride/N,N‐dimethylacetamide solvent system and acylated by ω‐undecenoyl chloride under microwave irradiation with N,N‐dimethyl‐4‐aminopyridine as the catalyst. Cellulose unsaturated fatty acyl esters with a degree of substitution (DS) ranging from 1.4 to 2.0 were then crosslinked by olefin metathesis with a first generation Grubbs catalyst. Crosslinking ratios (T) ranging from 20 to 90% were obtained for low catalyst amounts (<1.2%), but gels appeared when T was too high. To avoid this gel formation, cellulose was acylated with a mixture of lauroyl and ω‐undecenoyl chlorides. This internal dilution allowed us to obtain films of every case and various T (varying from 10 to 80% for a catalyst amount below 3.5%). Plastics were characterized by Fourier transform infrared (FTIR) spectroscopy, and the fatty acid mixture resulting from the hydrolysis of cellulose esters were analyzed by gas chromatography (GC) and NMR spectroscopy. Mechanical properties showed that the elastic modulus and tensile failure stress was higher when the plastic films were crosslinked. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 407–418, 2005     

Solvent impact on esterification and film formation ability of nanofibrillated cellulose

In this study we have manufactured nanofibrillar cellulose and modified the fibre surface with ester groups in order to hydrophobise the surface. Nanofibrillated cellulose was chosen to demonstrate the phenomena, since due to its high surface area the effects at issue are pronounced. The prepared NFC ester derivatives were butyrate, hexanoate, benzoate, naphtoate, diphenyl acetate, stearate and palmitate. X-ray photoelectron spectroscopy, solid state NMR and contact angle measurements were used to demonstrate the chemical changes taking place on the cellulose surface. NFC ester derivatives can be prepared after a careful solvent exchange to a water-free solvent medium has been carried out. Butyl and palmitoyl esters were chosen for film forming tests due to the difference in their carbon chain lengths, and their contact angles and water vapour and oxygen permeation rates were studied. The prepared nanocellulose esters show increased hydrophobicity even at very low levels of substitution and readily form films when the films are prepared from acetone dispersions. The permeation rates suggest a potential use as barrier materials.     

Accurate determination of the degree of substitution of long chain cellulose esters

The determination of the degree of substitution (DS) of fatty acid cellulose esters with alkyl chain lengths from C8 to C18 was performed by direct transesterification with trimethylsulphonium hydroxide (TMSH) using tert-butyl methyl ether (MTBE) as a solvent. Transesterification was demonstrated to be quantitative at 75 °C in 60 min. The quantification of the formed fatty acid methyl esters was performed by gas chromatography (GC). After the optimization of the method, long chain cellulose esters (LCCE) could be analyzed in a wide range of DS. The obtained values were compared to those given by other existing protocols. LCCE with DS-values in a range of 5 × 10⁻⁵ to 3 were analyzed with high accuracy. Reproducibility is weakened for high DS values if the sample has a compact aspect limiting the accessibility of TMSH to the ester functions. This method can also be suitable for the analysis of mixed cellulose esters.     

Microfibrillated cellulose/cellulose acetate composites: Effect of surface treatment

Microfibrillated cellulose (MFC), which consists of a web‐like array of cellulose fibrils having a diameter in the range of 10–100 nm, was incorporated into a cellulose acetate (CA) matrix to form a totally biobased structural composite. Untreated and a 3‐aminopropyltriethoxysilane (APS) surface treated MFC was combined with a CA matrix by film casting from an acetone suspension. The effectiveness of the surface treatment was determined by infrared spectroscopy and X‐ray photoelectron spectroscopy. The Young's moduli of APS treated MFC composite films increase with increasing MFC content from 1.9 GPa for the CA to 4.1 GPa at 7.5 wt % of MFC, which is more than doubled. The tensile strength of the composite film increases to a maximum of 63.5 MPa at 2.5 wt % compared to the CA which has a value of 38 MPa. The thermal stability of composites with treated MFC is also better than the untreated MFC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 153–161, 2010     

Zero-order release formulations using a novel cellulose ester

New carboxymethylcellulose esters were developed with useful properties for oral dosage forms in drug delivery. Normally, commercial cellulose esters are used as the major excipients in oral dosage forms as a coating or a membrane. In applications involving compression tablets, cellulose esters are usually mixed with other more hydrophilic matrix components to facilitate dissolution of the active. In the present study, novel cellulose esters were single component matrix resins. Pharmaceutical actives were cryogenically ground as a physical blend or an amorphous blend with the polymer. Subsequently, tablets were made by direct compression using a single tablet press, or capsules were made by filling them with the ground material. Dissolution tests were completed on the solid dosage forms at pH 1.2, 4.5, 6.8 or 7.4 in a United States Pharmacopeia (USP) II device to determine the release profiles for up to 24 h. Carboxymethylcellulose esters provide an excellent matrix for controlling both the rate of release and the pH at which pharmaceutical actives release into the aqueous environment. When used in suitable quantities, dictated by the active of interest, carboxymethylcellulose acetate butyrate provided zero-order release over sustained time up to 24 h.     

Interactions with water of mixed acetic-fatty cellulose esters

Cellulose powder was acylated with mixtures containing acetic, fatty and acetic-fatty anhydrides to form acetic-fatty cellulose esters. The total degree of substitution (DS) of the mixed cellulose esters (MCE) ranged from 2 × 10⁻² to 2.92. MCE were characterized by their interactions with water. Static contact angles with water were measured on a regular smooth surface. The values found were dependent on the fatty acyl content and independent of the acetyl content. In the case of acetic-oleic cellulose esters, the minimum DS of the oleoyl moiety required to obtain permanent water repellency was 3 × 10⁻⁴. The microporosity of the samples may account for this exceptional hydrophobic character. Nevertheless, water vapor adsorption measurements on powder samples revealed only a limited increase in hydrophobicity of the MCE compared to cellulose acetate with the same acetyl content. It was thus demonstrated that water repellency and vapor water adsorption are not correlated.     

Recent advances in molecuar and supermolecuar characterization of cellulose and cellulose derivatives

Recent advances between 1985 and early 1993 in the following topics of the characterization of molecular structure and molecular properties of cellulose and its derivates (CD) made in the authors' laboratories are briefly reviewed: (1) A theoretical basis of the assignment of carbonyl carbon peaks of ¹³C NMR spectra on cellulose acetate (CA) was given, especially when the total degree of substitution <<f>> is below 3. (2) Molar fractions of 8 kinds of unsubstituted and partially or fully substituted anhydroglucopyranose units were successfully determined for CA and sodium cellulose sulfate (NaCS). (3) The sequence distribution of substituted and unsubstituted anhydroglucopyranose units along a water–soluble CA chain was evaluated. (4) C₆-substituted (i.e., 6-O-acetyl) CA and C₂- and C₆-substituted CA were synthesized, and the full assignment of the ¹³C NMR spetrum of the former was given and a new method for evaluating the degree of substitution at C₆ position was proposed. (5) By destructing the intramolecular hydrogen bonding, cellulose becomes soluble in aq. sodium hydroxide. The specific supermolecular structure of aq. sodium hydroxide, dissolving mechanism, dissolved state and molecular parameters of cellulose in aq. sodium hydroxide were discussed. (6) The solubility behavior of CA with a wide range of total degree of substitution in solvents including water, acetone/water and acetone is controlled by the distribution of substitution and the supermolecular structure. (7) The existence of O₃-H … O'₅ intramolecular hydrogen bonds in a water-in soluble cellulose derivative with hydrophilic substituent (NaCEC) was confirmed by CP/MAS ¹³C NMR and deuteration IR method. At a relatively low degree of substitution the solubility of the derivative in water or aqueous alkali was mainly governed by considerable destruction of the intramolecular hydrogen bonds. (8) The persistence length q, evaluated directly by small-angle X-ray scattering (SAXS) on CA with different total degree of substitution <<f>> ranging from 0,8 to 2,9 confirmed definitely the conclusion drawn before by Kamide and Saito on the molecular rigidity of CD, especially the effect of <<f>> on q. (9) C₆-substituted CA shows different solubility towards dimethylacetamide and water at 20°C, as compared with C₂- and C₃-subsituted CA and C₂-, C₃- and C₆- substituted CA, whose <<f>> is ca. 0,6.     

Characteristics of thin cellulose ester films spin-coated from acetone and ethyl acetate solutions

Spin-coated films of cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB) and carboxymethylcellulose acetate butyrate (CMCAB) have been characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The films were spin-coated onto silicon wafers, a polar surface. Mean thickness values were determined by means of ellipsometry and AFM as a function of polymer concentration in solutions prepared either in acetone or in ethyl acetate (EA), both are good solvents for the cellulose esters. The results were discussed in the light of solvent evaporation rate and interaction energy between substrate and solvent. The effects of annealing and type of cellulose ester on film thickness, film morphology, surface roughness and surface wettability were also investigated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.