Cellulose Acetate Concentration Research Articles

Effect of preparation variables on morphology and pure water permeation flux through asymmetric cellulose acetate membranes

In this study, cellulose acetate (CA) ultrafiltration (UF) membranes were prepared using the phase inversion method. Effects of CA and polyethylene glycol (PEG) concentrations in the casting solution and coagulation bath temperature (CBT) on morphology of the synthesized membranes were investigated. Based on L 9 orthogonal array of Taguchi experimental design 18 membranes were synthesized (with two replications) and pure water permeation flux through them were measured. It was found out that increasing PEG concentration in the casting solution and CBT, accelerate diffusional exchange rate of solvent 1-methyl-2-pyrrolidone (NMP) and nonsolvent (water) and consequently facilitate formation of macrovoids in the membrane structure. Increasing CA concentration, however, slows down the demixing process. This prevents instantaneous growth of nucleuses in the membrane structure. Hence, a large number of small nucleuses are created and distributed throughout the polymer film and denser membranes are synthesized. Rate of water flux through the synthesized membranes is directly dependent on the size and number of macrovoids in the membrane structure. Thus, maximum value of flux is obtained at the highest levels of PEG concentration and CBT (10 wt.% and 23 °C, respectively) and the lowest level of CA concentration (13.5 wt.%). Analysis of variance (ANOVA) showed that all parameters have significant effects on the response. However, CBT is the less influential factor than CA and PEG concentrations on the response (flux).

Development of cellulose acetate based antimicrobial food packaging materials for controlled release of lysozyme

Antimicrobial packaging materials were obtained by incorporation of lysozyme into cellulose acetate (CA) films. In order to achieve controlled release of lysozyme, the structure of the films was changed from highly asymmetric and porous to dense by modulating the composition of the initial casting solution. The highest release rate, soluble lysozyme activity and antimicrobial activity were obtained with the film prepared from 5% CA solution including 1.5% lysozyme. Increasing CA content in the casting solution decreased the porosity of the films, hence, reduced the release rate, maximum released lysozyme activities and the antimicrobial activities of the films. In contrast, immobilized lysozyme activities and the tensile strength of the films increased. The incorporation of lysozyme did not cause significant reductions in tensile strength and elongation at break values except in films prepared with 15% CA. This study showed the good potential of asymmetric CA films to achieve controlled release in antimicrobial packaging.

Cocontinuous cellulose acetate/polyurethane composite nanofiber fabricated through electrospinning

AbstractCocontinuous cellulose acetate (CA)/polyurethane (PU) composite nanofibers were obtained through electrospinning of partially miscible CA and PU in 2:1 N,N‐dimethylacetamide (DMAc)/acetone mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were affected by component ratio in the binary mixtures. PU component not only facilitated the electrospinning of CA at CA concentration down to 12 wt%, but reinforced the tensile strength of CA/PU nanofibrous mats, while semirigid component CA in the composite nanofibers could greatly improve the rigidity and dimensional stability of CA/PU nanofibrous mats. In a series of nanofibrous mats with varied CA/PU composition ratios, CA/PU 20/80 showed excellent tensile strength and Young's modulus. The residual product after selective removal of any one of the components in CA/PU composite nanofibers by washing with proper solvent maintained the fiber structure but greatly reduced the fiber size, suggesting CA/PU composite fibers showed a cocontinuous nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Investigation on polyacrylonitrile/cellulose acetate blends

The molecular interactions of polyacrylonitrile (PAN) and cellulose acetate (CA) were investigated thoroughly via dilute solution viscometry in dimethylformamide (DMF) as a common solvent at 30°C. The intrinsic viscosities and viscometric interaction parameters were experimentally determined for both binary (polymer/ dimethylformamide) and ternary (PAN/CA/dimethylformamide) systems. As all investigated PAN/CA ternaries evidenced negative viscometric interaction parameter values (δb & δk <0), the existence of repulsive intermolecular interactions was deduced, and PAN/CA blends were assigned as immiscible. Moreover, the results of microscopy photograph analysis indicated that pure PAN film evidences a homophasic structure, and the size of the phase domain increases gradually with increases in CA. In DSC analysis, it was determined that the glass transition temperature of the blend film increased slightly with increases in the CA content of the blend film.

Dewetting and surface properties of ultrathin films of cellulose esters

Surface properties of ultrathin films of cellulose esters deposited onto silicon wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) films adsorbed or spin-coated onto Si wafers were annealed up to one week. Film stability was monitored by AFM. Dewetting has been observed for CA and CAP. Only CAB films with lower degree of esterification presented dewetting, CAB films with high degree of butyrate were stable even after one week annealing. Surface energy of CA, CAP, and CAB was indirectly determined by contact angle measurements using drops of water, formamide and diiodomethane. The surface energy decreased as the size of alkyl ester group or the degree of esterification increased because van der Waals interactions became weaker. Effective Hamaker constant A eff was calculated for CA, CAP, and CAB onto Si wafers in air. Negative values of A eff were found for CA, CAP, and lower butyrate content CAB, which are related to instability and agree with dewetting phenomena observed by AFM. In contrast, a positive A eff was determined for higher butyrate content CAB, corroborating with experimental observations.

Viscoelastic Behavior of Cellulose Acetate in a Mixed Solvent System

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.

Effect of formulation parameters on the release characteristics of propranolol from asymmetric membrane coated tablets

Controlled delivery of drugs has been achieved successfully by use of asymmetric membranes. In our study, we have evaluated the influence of various preparation parameters such as concentration of the polymer, concentration of the pore former and temperature of the precipitation bath on the permeability and the release characteristics of propranolol. Propranolol tablets were prepared by direct compression and were coated with varying concentrations of cellulose acetate and glycerin. The coat was precipitated in water, maintained at various temperatures, followed by air drying of the coat. Scanning Electron Microscopy (SEM) was used to characterize the asymmetric structure of the membrane. The influence of various preparation parameters on the release of propranolol from asymmetric coated tablets was evaluated. SEM confirmed the asymmetric nature of the membrane. A zero order release of propranolol was obtained from the coated tablets of propranolol. Various preparation parameters studied significantly affected ( p < 0.05) the release of propranolol hydrochloride from the asymmetric membrane coated tablets and the release was independent of the pH and the rate of agitation of the dissolution medium ( p > 0.05). Asymmetric membranes can be successfully utilized in the controlled delivery of highly water soluble drugs like propranolol and by modifying preparation parameters like polymer concentration, pore former concentration and temperature of the precipitation bath, desired release rates can be obtained.

Studies on Permeation, Rejection, and Transport of Aqueous Poly(ethylene Glycol) Solutions using Ultrafiltration Membranes

The permeate flux and retention of aqueous solutions of poly(ethylene glycols) (PEG) with different molecular weights ranging from 4000 to 35,000 Da have been investigated using various compositions such as 100/0, 90/10, 80/20, and 70/30 wt% of cellulose acetate (CA)/sulfonated poly(etheretherketone) (SPEEK) ultrafiltration blend membranes. The factors affecting the rejection rate and permeate flux such as molecular weight of PEGs, concentration of the solute, composition of the membranes, and transmembrane pressures have been studied. It is seen that the increase in the concentration of PEG results in the decreased permeate flux and increased rejection for increasing CA content in the membranes. A similar observation in the flux and rejection was made for increasing the molecular weight of PEGs. Further, the mass transfer, diffusion, and true retention coefficients of the solute have been studied with different operating variables like molecular weight and concentration of PEGs. An increase in the molecular weight of PEGs results in the decrease of mass transfer and diffusion coefficients and increase of the true retention coefficient. A reverse trend is observed with increasing concentrations of PEG.

Enzymatic degradation of poly ( ε-caprolactone) and cellulose acetate blends by lipase and α-amylase

Films of poly( ε-caprolactone) (PCL) and cellulose acetate (CA) containing different proportions of PCL/CA (100/0, 80/20, 60/40, 40/60, 20/80 and 0/100, w/w) were prepared by casting, and their degradation by two enzymes (lipase and α-amylase) was monitored by mass loss and light microscopy for 240 days. Significant degradation was seen only in samples digested with lipase. Lipase selectively degraded PCL, with the rate of degradation being inversely proportional to the CA content. Light microscopy indicated some changes in morphology in the samples after digestion with lipase, and a relationship between these changes and the degree of mass retention—the larger the percentage of PCL in blends, the greater the loss of mass. However, there was no difference in the morphology among the samples incubated with α-amylase. The results suggested that lipase acts selectively on PCL, with little effect on CA.

Propranolol Hydrochloride Osmotic Capsule with Controlled Onset of Release

Hard gelatin capsule was coated by a cellulose acetate as a semipermeable membrane with or without castor oil and filled with propranolol hydrochloride and sorbitol as an osmotic agent. After sealing the capsule with white bees wax plug, the onset of release and dissolution rate of the drug were studied. Water penetration into the capsule from the dissolution medium increases simultaneously the osmotic and hydrostatic pressures of its content. When the hydrostatic pressure is high enough to overweigh the gravity and frictional forces of the plug, the expulsion of the plug occurs and drug release starts. The effects of thicknesses of the membrane and plug as well as the concentrations of cellulose acetate and castor oil on the onset of drug release were presented by a polynomial model. We found that the effect of plug thickness on the onset of release is more important when the membrane is thicker. The results showed that the presence of caster oil in coating formulation (cellulose acetate 10% or 15%) increased the onset of release (to values). The onset of release varied from 0.6 to 10.5 hr among which the onset times of 4.2, 4.8, 5.9, 5.5, 7.5, 5.0, 7.8 and 10.5 hr could be of use for either chronotherapeutic purposes in protection of patients against heart attacks and strokes during early morning hours or reducing daily frequency of dosage.

Electrospinning of Cellulose Acetate in Solvent Mixture N,N-Dimethylacetamide (DMAc)/Acetone

Electrospinning of cellulose acetate (CA) was studied in relation to factors of solvent composition, size of spinnerete orifice, viscosity, and molecular weight. It was found that cellulose acetate nanofibers were obtained from solvent mixture N,N-dimethylacetamide (DMAc)/acetone with volume ratio of 2:1 and 1:2. Beaded nanofibers were more likely formed from solvent 2:1 DMAc/acetone, whereas bead-free CA nanofibers were produced at lower CA concentration in 1:2 DMAc/acetone. The size of spinnerete orifice showed no significant effect on the mean diameter of CA nanofiber, but small size of spinnerete orifice often resulted in nanofibers with large fiber size distribution. With respect to the effect of molecular weight on electrospinning, nanofibers of CA-398-3 (Mw=3.0×104) had wide size distribution of 90–790 nm with large amounts of big spindle-like beads along fibers. The diameters of nanofibers from CA-398-6 (Mw=3.5×104) were in the range of 90–430 nm with a few conical shape beads on fiber. In the case of CA-398-10 (Mw=4.0×104), its nanofiber diameters increased to 90–550 nm without noticeable bead defects. The water contact angles of nanofibers of CA-398-3, CA-398-6 and CA-398-10 were 81°, 50.5° and 40.4°, respectively, suggesting the orientation of hydrophobic and hydrophilic groups on the very outer fiber surface got changed when CA fiber size is down to nanometer range. The interconnected pore volume of CA nanofibrous membranes is tripled with CA molecular weight increasing from 3.0×104 to 4.0×104.

Studies on Performance of Cellulose Acetate and Poly(Ethelene Glycol) Blend Ultrafiltration Membranes Using Mixture Design Concept of Design of Experiments

Cellulose acetate (CA) membranes have several advantages over other membranes due to their moderate flux, high salt rejection properties, renewable source of raw material, etc. Membrane compositions containing different concentrations of CA, polyethylene glycol (PEG 600) as additive and N,N–dimethyl formamide (DMF) as solvent have been prepared using phase inversion technique based on the mixture design concept of design of experiments. The prepared membranes have been characterized for permeate flux, membrane hydraulic resistance, and separation of proteins such as pepsin, egg albumin (EA), and bovine serum albumin (BSA). Using statistical techniques, the experimental data have been analyzed and a suitable model was suggested for predicting the optimal level of response as a function of the input variable. The influence of variation of the CA, DMF, and PEG 600 on the asymmetric membrane properties has also been reported.

Biodegradability of PMMA Blends with Some Cellulose Derivatives

High polymer blends of Polymethyl methacrylate (PMMA) with cellulose acetate (CA) and Cellulose acetate phthalate (CAP) of varying blend compositions have been prepared to study their biodegradation behavior and blend miscibility. Films of PMMA–CA, and PMMA–CAP blends have been prepared by solution casting using Acetone and Dimethyl formamide(DMF) as solvents respectively. Biodegradability of these blends has been studied by four different methods namely, soil burial test, enzymatic degradation, and degradation in phosphate buffer and activated sludge degradation followed by water absorption tests to support the degradation studies. Degradation analysis was done by weight loss method. The results of all the tests showed sufficient biodegradability of these blends. Degradability increased with the increase in CA and CAP content in the blend compositions. The miscibility of PMMA–CA and PMMA–CAP blends have been studied by solution viscometric and ultrasonic methods. The results obtained reveal that PMMA forms miscible blends with either CA or CAP in the entire composition range. Miscibility of the blends may be due to the formation of hydrogen bond between the carbonyl group of PMMA and the free hydroxyl group of CA and CAP.

Preparing highly porous chitosan/cellulose acetate blend hollow fibers as adsorptive membranes: Effect of polymer concentrations and coagulant compositions

In this work, we report the study on the effect of fabrication factors influencing the structures and morphologies of the chitosan and cellulose acetate blend hollow fibers as adsorptive membranes to achieve highly porous and macrovoids-free structures with different pore sizes. The factors investigated include chitosan (CS) and cellulose acetate (CA) concentrations in the spinning dope solutions, and the composition of the external and internal coagulants. For CA concentration at 12–18 wt% and CS concentration at up to 4 wt% in the spinning dope solutions, the blend hollow fibers were successfully prepared with outer surface pore sizes, specific surface areas and porosities in the range of 0.54–0.049 μm, 10.4–14.5 m 2/g and 80.6–70.4%, respectively, depending on the CA and CS amounts in the spinning dope solutions and the coagulants used. Water, a weaker coagulant, can be used as both the external and internal coagulants in the fabrication process and the resultant CS/CA blend hollow fibers showed spongy-like, macrovoids-free and relatively uniform porous structures which are desirable for adsorptive membranes. By increasing the alkalinity of the coagulants, the coagulation rate of the blend hollow fibers was increased and the hollow fibers were observed to form relatively denser surface layers and to have smaller surface pore sizes and slightly greater specific surface areas, due to the stronger coagulation effect. Particularly, when NaOH solutions (1–3 wt%) were examined as the internal coagulant, more and larger macrovoids were formed in the blend hollow fibers at the near lumen side with the increase of the NaOH concentrations at low CS concentrations (<3 wt%), indicating the importance of coagulant compositions and polymer concentrations in the fabrication of adsorptive CS/CA blend hollow fibers with uniform porous structures.

Cellulose Acetate/Chitosan Multimicrospheres Preparation and Ranitidine Hydrochloride Release In Vitro

A noval cellulose acetate/chitosan multimicrospheres (CACM) was prepared by the method of w/o/w emulsion. The concentration of cellulose acetate (CA) and the ratio of CA/chitosan (CS) had influence on the CACM size, and appearance. Ranitidine hydrochloride loading, and releasing efficiency in vitro were investigated. The optimal condition for preparation of the microspheres was CA concentration at 2% and the ratio of CA/CS at 3/1. The microspheres size was 200–350 μm. The appearance of microspheres was spherical, porous, and nonaggregated. The highest loading efficiency was 21%. The ranitidine release from the CACM was 40% during 48 hr in buffers.

Isothermal Crystallization Kinetics of Poly (Ethylene Terephthalate) ? Cellulose Acetate Blends

The isothermal crystallization exotherm was determined at three temperatures for two blends of bottle regrind Poly(ethylene terephthalate) (PET) with Cellulose Acetate (CA) as derived by an extrusion process, as well as for the pristine PET. It was observed that the addition of 10 weight-percent CA increased the crystallization rate of PET manifold, which resulted in improved moldability with faster cycle times. The crystallization was observed to be very fast with initiation times of the order of a few seconds, perhaps due to the impurities present in the bottle regrind PET and the synergistic effects of the CA particles. The fast rate of crystallization and high melting point of PET (250 C), and the degradation of CA at temperatures higher than 260 C made extrusion of PET – CA blends difficult. However, increasing the CA content in the blend to 30% decreased the rate of crystallization of PET resulting in an improved extrusion process, but slower cycle times.

Formation of micro- and nano-spheric particles (filter dust) during the preparation of cellulose acetate membranes

Membranes were prepared from six samples of cellulose acetate (CA) differing in their average molecular weight (75–260 kg/mole) and molecular weight distribution using methyl acetate as solvent and 2-propanole as precipitant. The routes through the phase diagram and the evaporation times were varied in these experiments. Electron microscopy demonstrates that the amount of filter dust (CA particles deposited on the membrane surface) decreases as the fraction of low molecular weight material in the starting polymer becomes less. For low average molar mass of CA and moderate polymer concentrations in the casting solution the dust consists of individual spheres of relatively uniform size (1–2 μm) which cover the surface in a number of layers. With rising molar mass of the polymer the dust particles consist increasingly of strings of cohering and deformed beads of comparable size. Under these condition, some considerably smaller particles (≤0.1 μm) are also formed. Possible mechanisms of filter dust formation are discussed and measures for its prevention are proposed.

Mass transfer dynamics of the evaporation step in membrane formation by phase inversion

AbstractA ternary diffusion model has been developed for the evaporation step of the phase inversion process. The model is applied to the analysis of mass transfer dynamics of the evaporation step for the methanol–acetone–cellulose acetate (CA) ternary casting system. The combined analysis of quantitatively computational results from the ternary evaporation model and qualitative dynamic results during the quench process has shown that the evaporation step is essentially necessary to prepare the defect‐free, ultrathin skinned asymmetric CA membrane for the separation of CO2/CH4. The skin layer of high CA concentration obtained by evaporation has an ability to suppress liquid–liquid phase separation. And the skin layer with high tensile strength can resist the interfacial tension caused by spinodal decomposition from the substructure. Although the CA concentration in the skin layer increases considerably because of the evaporation step and the following delay time during the quench process, the substructure can still induce the spinodal decomposition because the strong coagulant, methanol, can diffuse rapidly across the ultrathin skin layer. Hence the defect‐free, ultrathin‐skinned asymmetric membrane for gas separation can be prepared from methanol–acetone–CA casting system by evaporation step and the wet phase inversion. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1564–1571, 2002

Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

AbstractThree 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

Diffusional characteristics of sodium chloride in symmetrical cellulose acetate membranes measured by an unsteady-state dialysis method

Unsteady-state dialysis and steady-state reverse osmosis (RO) experiments for aqueous NaCl solutions were carried out with cellulose acetate (CA) symmetrical membranes. The distribution and overall diffusion coefficients of NaCl, K and D were obtained from the unsteady-state dialysis experimental data, taking the effect of osmosis into consideration. D was found to increase with the increase of the solute concentration. The concentration dependency of D can be explained by applying a two-part (perfect or dense and imperfect or porous) model of the membrane. The concentration independent diffusion coefficients of NaCl in the dense part D d and in the porous D p are obtained from the assumption of the two-part model for the membrane. D d does not depend on the water content in the membrane W w , but on dope composition. Contrary to D d , D p increases with the increase of W w and can be correlated only with W w and D p ( W w =0) is found almost equal to the averaged D d for each type of membrane: D p,c = D d exp ( γ × W w ). It seems from these facts that the structure of membrane becomes tight with the decrease of the ratio of formamide to CA and loose with the decrease the concentration of CA in dope solutions. D c(c = 0) at the zero concentration can be calculated as follows: D c (0) ≈ W w D p,c + (1−W w) D d . Solute permeability ω obtained by RO experiments agrees well with ω c = [K · D c (0)] (ℓ · β) , those calculated from D c (0) and distribution coefficient K.