Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter δ, surface tension γ, viscosity η and boiling temperature were used to generate mixtures for electrospinning cellulose acetate (CA) (degree of substitution, DS = 2.45). Although none of these solvents alone enables continuous formation of fibers, mixing DMAc with either acetone or acetic acid produced suitable solvent systems. The 2:1 acetone:DMAc mixture is the most versatile mixture because it allows CA in the 12.5–20% concentration range to be continuously electrospun into fibrous membranes. These CA solutions have η between 1.2 and 10.2 poise and γ around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to ～1 μm. Fiber sizes generally decrease with decreasing CA concentrations. The nature of the collectors affects the morphology as well as packing of fibers. Fibers collected on paper have more uniform sizes, smooth surfaces, and fewer defects, whereas fibers collected on water are more varied in size. Electrically conductive solid collectors, such as Al foil and water, favor more tightly packed and less porous membranes. Porous collectors, like paper and copper mesh, produce highly porous membranes. The pores in membranes collected on the Al foil and paper are much better interconnected in the planar directions than those in membranes collected on water. There is evidence that electrospinning induces order in the fibers. Deacetylation of CA membranes is more efficient and complete in NaOH/ethanol than in aqueous NaOH, producing DS values between 0.15 and 2.33 without altering fiber surfaces, packing, or organization. The fully regenerated cellulose membranes are similarly hydrophilic as commodity cellulose fibrous matrices but absorb nearly 10 times as much water. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119–2129, 2002     

Starch cellulose acetate co-acrylate (SCAA) polymer as a drug carrier

The present study aims to create a controlled-release system through the preparation and characterization of starch cellulose acetate co-acrylate (SCAA) polymer for application as a carrier for cancer drugs. SCA was prepared from maize starch and different ratios of cellulose acetate. The obtained product SCA was reacted with acrylic acid monomer to give cellulose acetate co-acrylate. The best ratio of starch to cellulose acetate was found to be 90:10, giving a stable product with acrylic acid. The cancer drug 8-(2-methoxyphenyl)-3,4-dioxo-6-thioxo-3,4,6,7-tetrahydro-2h-pyrimido[6,1-c]-[1,2,4]triazine-9-carbonitrile was dissolved in dimethylformamide then added gradually at the end of the previous reaction under stirring for 15 min. The prepared polymers with and without the drug were characterized by Fourier-transform infrared spectroscopy. Cuboids discs of the prepared polymer/drug were subjected to drug release in aqueous media at different pH values. The release was measured spectrophotometrically. It was found that the release rate depends on the pH of the aqueous medium as well as on the concentration of the drug loaded onto the polymer carrier. Above pH 12, the polymer containing the drug degraded completely within 1 h after being subjected to alkaline media. Sustained release of drug extended to about 20 days. The amount released depended on the pH of the media in the following order: basic media > acidic media > neutral. According to Higuch’s equation, the diffusion coefficient was found to be 4.2 × 10^?8 and 5.5 × 10^?8 cm s^?1 for the two evaluated concentrations (1.5 and 2 %) of active organic compound (drug).     

Synthesis and characterization of carboxylate waterborne cellulose emulsion based on cellulose acetate

With cellulose acetate (CA) as a base material, a novel environmentally friendly carboxylate waterborne cellulose acetate (CWCA) emulsion was synthesized via the method of self-emulsification. Taking advantage of acrylic acid, hydroxyethyl acrylate as a modifier, and isophorone diisocyanate as a bridging agent, the molecular structural design of CWCA dispersion was completed successfully, and the structure was confirmed by Fourier transform infrared spectroscopy (FTIR). In this work, the particle size and distribution of the stable CWCA dispersion with solid content of 22.6% are 115.6 and 0.158 nm, respectively. It was found that the microstructure of emulsion particles is a core-shell structure containing a hydrophilic carboxylate group as the shell and hydrophobic cellulose acetate molecular as the core. In addition, the hydrophobic behavior of CWCA film is presented as a contact angle of 109.9°. Furthermore, CWCA film provided a higher thermal decomposition temperature of 345.42 °C than that of CA film at the largest mass loss rate.     

Application of cellulose acetate butyrate-based membrane for osmotic drug delivery

The release rate of drugs from an OROS^® is controlled by semipermeable membranes composed typically of cellulose acetate (CA) with various flux enhancers. Cellulose acetate butyrate (CAB) was identified as a viable alternative. The CAB membrane matched the CA membrane in robustness but had superior drying properties, offering particular advantages for thermolabile formulations. Studies were conducted to characterize CAB membrane properties with respect to performance of OROS^® systems. Four different membrane formulations with varying plasticizer type and concentration were investigated. The CAB based membranes exhibited superior drying characteristics and similar functionality to the CA:polyethylene glycol (PEG) membranes used as a control. A linear relationship was observed between the level of flux enhancer and release rate. The stability of the membrane was evaluated based on release profiles after system storage at various conditions. The CAB membranes appeared to have stability comparable to the standard CA membrane. A linear relationship between membrane weight and release rate as well as the time required to release 90% of a drug from the system [T₉₀] for a model formulation was observed. In conclusion, the newly identified alternative membrane composition allows for the use of thinner membranes, thereby reducing cost of goods, coating time and, most importantly, membrane drying time.     

Zero-order drug release cellulose acetate nanofibers prepared using coaxial electrospinning

Novel drug-loaded cellulose acetate (CA) nanofibres were prepared by a modified coaxial electrospinning process, after which their zero-order drug release profiles were determined. Using 2 % (w/v) unspinnable CA solution as a sheath fluid, coaxial electrospinning can be conducted smoothly to generate ketoprofen (KET)-loaded CA nanofibres coated with a thin layer of blank CA. Scanning electron microscopy images demonstrated that nanofibres obtained from the modified coaxial process have a smaller average diameter, a narrower size distribution, more uniform structures, and smoother surface morphologies than those generated from single-fluid electrospinning. Transmission electron microscopy observations demonstrated that the nanofibres have a thin coating layer of blank CA on their surface with a thickness of ca. 15 nm. X-ray diffraction and differential scanning calorimetry verified that KET molecules in all of the nanofibres presented an amorphous state. Fourier transform infrared spectra demonstrated that CA has good compatibility with KET, which is brought about by hydrogen bonding. In vitro dissolution tests showed that the nanofibres coated with blank CA have no initial burst release effects and can provide a zero-order drug release profile over 96 h via a diffusion mechanism. The modified coaxial electrospinning method can provide new approaches in developing cellulose-based nano products with definite structural characteristics and improved functional performance.     

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.     

Hybrid electrospun nonwovens from chitosan/cellulose acetate

Co-mixtures of chitosan (CS) and cellulose acetate (CA) were electrospun into fibrous webs from a binary co-solvent containing 70:30 trifluoroacetic acid (TFA): methylene chloride (DCM). Fibrous webs were produced from CS/CA in ratios (wt%) of 20:80, 40:60, 50:50 and 60:40. As determined by SEM analysis, 12% polymer solutions of CS/CA 60:40 produced structures with uniform bead free fibre morphologies with an average fibre diameter of 458 nm. FTIR-spectroscopy confirmed the presence of CS in the as-spun fibres in the form of chitosan-amine trifluoroacetate salts (NH₃ ⁺CF₃COO⁻). Uniform mixing of the CS and CA components was confirmed by DSC analyses. Alkaline neutralisation of the chitosan amine salts was explored as a means of increasing wet stability. The as-spun fibres were found to be relatively unstable in aqueous medium due to the solubility of the chitosan amine salts. Alkaline post-neutralisation was evaluated as means of minimising weight loss and maximising retention of fibrous structure.     

Development of an enantioselective membrane from cellulose acetate propionate/cellulose acetate,for the separation of trans-stilbene oxide

This paper reports the characterization of new synthesized chiral polymeric membranes, based on a cellulose acetate propionate polymer. The flux and permselective properties of the membrane were studied using 50 % ethanol solution of (R,S)-trans-stilbene oxide as feed solution. Scanning electron microscopy revealed the asymmetric structure of these membranes. The roughness of the surface was measured by atomic force microscopy. The resolution of over 97 % enantiomeric excess was achieved when the enantioselective membrane was prepared with 18 wt% cellulose acetate and 8 wt% cellulose acetate propionate in the casting solution of dimethyl formamide/N-methyl-2-pyrrolidone/acetone, at 20 °C and 55 % humidity, and a water bath at 10 °C for the gelation of the membrane. The operating pressure and the feed concentration of the trans-stilbene oxide were 275.57, 345.19, and 413.84 kPa and 2.6 mM, respectively.     

Electro-osmosis of water through a cellulose acetate membrane

Experiments on electro-osmosis of water through a cellulose acetate membrane have been reported and the data analyzed in the light of nonequilibrium thermodynamics. The linear phenomenological equations have been found to be valid. Study of the directional dependence of phenomenological coefficients has revealed the anisotropic character of the membrane. Efficiency of energy conversion for both electro-osmosis and streaming potential has been calculated and the results have been analyzed in the light of thermodynamic theories.     

Synthesis and characterization of cellulose acetate from cellophane industry residues. Application as acetaminophen controlled-release membranes

Journal of Thermal Analysis and Calorimetry - Cellophane film production generates cellulosic residues from scraps, edges, and low-quality films. In this work, cellophane was used as a raw material...     

Synthesis and characterization of hydroxypropyl cellulose from bacterial cellulose

Bacterial cellulose produced by Acetobacter xylinum has been reacted with propyleneoxide to synthesize hydroxypropyl cellulose(HPC) under different reaction conditions while diluted by toluene. The effects of mass ratio of bacterial cellulose to propyleneoxide, dilutability of toluene, reaction temperature(T) and time(t) were investigated by series of experiments. The degree of substitution(DS), hydroxypropyl content(A) and yield(η) were compared. The optimized product exhibited cold-water solubility and hot-water gelatinization in aqueous medium. Further study was carried out with FTIR, TGA, XRD, SEM and 13C-NMR for characterization. The water/air contact angle measurement reveals that it is a good hydrophobic material with good mechanical properties.     

纤维素醋酸酯的均相合成

纤维素的非均相反应取代不均匀、产率低。本文用纤维素在LiCl／DMAc溶液中的均相反应。制得了纤维素三醋酸酯(CTA)、纤维素二醋酸酯(CDA)、纤维素—醋酸酯(CMA),并对产品结构性能进行了表征。     

Photodegradation of cellulose acetate fibers

The photodegradation of cellulose acetate fibers by ultraviolet light in vacuo at 77°K and at ambient temperature was studied. Three kinds of light sources with different wavelengths between 2353 and 6000 Å were employed. ESR studies at 77°K show that several kinds of free radicals are produced from cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers when irradiated with light of wavelength shorter than 2800 Å. Among these methyl radicals formed decayed within 210 min at 77°K. When the temperature was raised above 77°K, radical transformation occurred at 87°K and most of the free radicals decayed at 193°K, whereas the cellulosic radicals were stable at this and even at higher temperatures. Ultraviolet spectroscopy studies revealed that the main chromophores are the carbonyl function of the acetyl group and acetal groups in the polymer. The photodegradation of the polymers at ambient temperature resulted in the formation of gaseous products (mainly CO, CO₂, and CH₄), together with the loss of bound acetic acid content and sample weight. Decreases in viscosity and reduction of tensile strength and elongation were also observed in the irradiated samples, revealing that the overt effects of ultraviolet light on cellulose acetate fibers are interpreted in terms of free-radical reactions ultimately leading to main-chain and side-group scissions, unsaturation, and the formation of small molecule fragments. Among these, main-chain scission took place predominantly in CDA fiber and side-group scission in CTA fiber. The mechanism of the fundamental photochemical degradation processes of cellulose acetate fibers is elucidated.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

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     

Moisture absorption measurement and modelling of a cellulose acetate

Cellulose - With a view toward the application of highly hygroscopic polymers as a humidity responsive self-actuator, the evaluation of the real time moisture concentration in the material becomes...     

Synthesis and characterization of microcrystalline cellulose produced from bacterial cellulose

In this study, microcrystalline cellulose (MCC) was prepared from the acid hydrolysis of bacterial cellulose (BC) produced in culture medium of static Acetobacter xylinum. The MCC-BC produced an average particle size between 70 and 90 μm and a degree of polymerization (DP) of 250. The characterization of samples was performed by thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The MCC shows a lower thermal stability than the pristine cellulose, which was expected due to the decrease in the DP during the hydrolysis process. In addition, from X-ray diffractograms, we observed a change in the crystalline structure. The images of SEM for the BC and MCC show clear differences with modifications of BC fiber structure and production of particles with characteristics similar to commercial MCC.     

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.     

Synthesis and characterization of photosensitive cinnamate-modified cellulose acetate butyrate spin-coated or network derivatives

The photochemical behavior of photosensitive materials obtained by spin-coating or network synthesis of a cellulosic polymer bearing photo-cross-linkable cinnamate groups was investigated. First, cinnamate groups were grafted on a cellulose acetate butyrate polymer, with different grafting densities. The photochemical properties of the polymers were studied in solution by UV–visible and ¹H NMR spectroscopy. Then spin-coated films and networks were prepared and characterized as a function of the number of cinnamate groups per cellulosic unit. The water-wetting properties of both surfaces were studied by dynamic contact angle measurements, before and after photoirradiation, and subsequent heating. The surfaces obtained by the two methods have significantly different behaviors that can be assigned to the distinct photochemical pathways of the cinnamate groups upon irradiation depending on the sample preparation. Indeed, dimerization reaction is evidenced as the main process in the spin-coated films while the expected isomerization is predominant at the surface of the polymer networks.     

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.