Ethylcellulose Solution Research Articles

Molecular Dynamics in Dilute Aqueous Solutions of Ethyl(hydroxyethyl)cellulose and Sodium Dodecyl Sulfate As Investigated by Proton NMR Relaxation

Dilute aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) and sodium dodecyl sulfate (SDS) have been investigated by 1H NMR shift and relaxation measurements. The shift measurements indicate no presence of EHEC at the core of the SDS micelles but at and just inside the micellar surface. Both the spin−lattice relaxation time (T1) and the spin−spin relaxation time (T2) imply that molecular motions slow as the system aggregates. T1 measured at both 270 and 400 MHz indicates nonextreme narrowing conditions with molecular motions on the nanosecond time scale. T2 monitors slower dynamics of the EHEC/SDS/water as compared to both of the systems polyethylene oxide (PEO)/SDS/water and SDS/water, attributed to the rigid EHEC backbone as compared to the more flexible PEO chain. An important observation is that the NMR relaxation data correlate well with the microviscosity in the EHEC/SDS/water system as measured by intramolecular excimer formation of the fluorescent probe 1,3-di(1-pyrenyl)propane (P3P).

A Surface Force, Light Scattering, and Osmotic Pressure Study of Semidilute Aqueous Solutions of Ethyl(hydroxyethyl)celluloseLong-Range Attractive Force between Two Polymer-Coated Surfaces

Semidilute (above the overlap concentration, c*) aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) as a function of concentration were investigated with the surface force apparatus (SFA), and by static light scattering (SLS) and osmotic pressure measurements. The anomalous excess in scattering intensity observed in SLS experiments at small angles indicates concentration inhomogeneities in the samples, probably as a result of association of the EHEC chains. The light scattering and osmotic pressure results show that EHEC in aqueous soluttion does not behave as expected for a polymer in a good solvent. The results from the SFA experiments show that EHEC adsorbs strongly on mica. These adsorbed layers give rise to a short-range steric repulsion when the two EHEC-coated mica surfaces are brought into close contact. The most remarkable result, however, is the very long-range attractive force observed at larger surface separations. This attractive force features oscillations with a periodicity that decreases when the polymer concentration increases. The periodicity corresponded to the mesh network size determined by SLS. To our knowledge, this type of long-range attraction has not previously been reported. The origin of the force could not be explained in terms of bridging or classical depletion effects. Rather, this long-range attraction might be induced by segregation of different polymer fractions, with different surface activities, present in the EHEC solutions.

An NMR Self-Diffusion Investigation of Aggregation Phenomena in Solutions of Ethyl(hydroxyethyl)cellulose.

Water solutions of ethyl(hydroxyethyl)cellulose have been investigated with the PFG NMR technique and by means of 1H NMR relaxation measurements. The echo decays in PFG experiments have been recorded for EHEC with concentrations ranging from the dilute (c < c) to the semidilute (c > c). In addition, the temperature dependence of the echo decay was investigated. It is shown that the echo decays deviate substantially from Gaussian diffusion behavior. We discuss this in terms of polydispersity, aggregation, and scaling effects. It is argued that the observed deviations are too large to be caused by polydispersity effects alone. We base this conclusion on the observation that the molar mass scaling of the polymer diffusion coefficient goes roughly as M-4. We focus on using a log-normal distribution of diffusion coefficients in the evaluation procedure of the PFG data. It is found that by comparing the diffusion coefficients extracted from this type of procedure with "Dmean" as extracted from a "stretched exponential" approach, there is a difference in the evaluated diffusion constant by up to 1 order of magnitude. The difference depends on the degree of deviation from linear behavior in the echo decay when represented in a logarithmic plot vs the relevant experimental parameter.

Aqueous Solutions of Ethyl (Hydroxyethyl) Cellulose and Hydrophobic Modified Ethyl (Hydroxyethyl) Cellulose Polymer: Dynamic Surface Tension Measurements

The dynamic surface tension of aqueous solutions of ethyl (hydroxyethyl) cellulose (EHEC) and hydrophobic modified ethyl (hydroxyethyl) cellulose (HM-EHEC) were determined using the maximum bubble pressure method. Values were monitored over surface lifetimes ranging from 0.15 to 2.5 s (after dead time corrections). In the low concentration range (<100 ppm) HM-EHEC was shown to be more surface active, and the presence of salt (0.1M) was shown to increase the surface activity of both polymer systems. The results were compared with surface tension measurements carried out over longer time scales, determined using the du Nouy ring technique. From these results, isotherms were constructed relating surface tension to surface aging time. Although the results could not be directly correlated to interfacial diffusion models, the isotherms were found to be comparable to previous data reported for lower-molecular-weight poly(oxyethylene ether) surfactants and a higher-molecular-weight EHEC polymer determined using the pendant drop technique. Essentially, the isotherms could be divided into distinct regions: induction period, fast fall region where surface coverage occurs fairly rapidly, and finally the meso-equilibrium region. From the Gibbs equation, the number of segments of polymer per unit surface area at saturated adsorption levels was calculated over regions of different aging times, and the results are discussed in terms of configuration changes of the polymer at the interface.

Structural transitions in liquid crystalline solutions of some cellulose derivatives

It was found that the domains of the mesophase of the investigated systems have cylindrical symmetry and a different direction of the maximum polarizability: for ethylcellulose and cellulose diacetate, the polarizability is directed along the axis of the cylinder, while it is at an angle of 45‡ for hydroxypropylcellulose. Formation of liquid-crystalline spherulites in the thermotropic transition of isotropic solutions of ethylcellulose in formic acid to the mesophase was demonstrated. In the liquid crystal—isotropic liquid phase transition, a characteristic extreme of the intensity of light scattering is observed near the region of melting of the liquid crystalline matrix, so that this method can be used for identifying the region of the existence of a two-phase “corridor”.

Association of Ethyl(hydroxyethyl)cellulose Solutions

Ethyl(hydroxyethyl)cellulose (EHEC) forms true molecular solutions in 10 mM aqueous solution NaCl at concentrations equal or less than 0.1%. Less hydrophilic EHEC forms true molecular solution also in methanol/10 mM aqueous NaCl (1:1, v/v) mixture. An associative clustering was observed in this solvent mixture in the case of a more hydrophilic EHEC derivative. The amount and size of clusters increased with EHEC sample concentration. Repulsive forces related to some minute charge of EHEC, evidenced by ion-exclusion chromatography in the absence of salt in the methanol/water (1:1, v/v) mobile phase, became operative in clustering solution without salt; both the amount and size of clusters decreased. EHEC contains a low amount of particle impurities. The light-scattering signal related to these impurities may be misinterpreted as an aggregation when the solutions are not properly filtered.

Spectroscopic behaviour of 8-hydroxy-1,3,6-pyrenetrisulphonate immobilized in ethyl cellulose

The spectroscopic behaviour of 8-hydroxy-1,3,6-pyrenetrisulphonate (HPTS) immobilized in an ethyl cellulose film and in aqueous phosphate pH buffers have been studied using fluorescence and electronic absorption spectra. The absorption, excitation and emission peak maxima of the acidic and basic forms of HPTS in ethyl cellulose and aqueous solution have been determined and compared. The deprotonation of the excited acidic form of HPTS is suppressed in ethyl cellulose but not in aqueous solution condition. HPTS in an aqueous solution is more acidic than in an ethyl cellulose film. Less number of water molecules and salt effect in ethyl cellulose are used to explain this observation. The acid dissociation constants of HPTS in an aqueous phosphate solution and an ethyl cellulose film are 7.31 and 8.43, respectively at 25°C.

Rheology of ethyl cellulose solutions

AbstractSteady state flow and dynamic viscoelastic measurements of ethyl cellulose / m‐Cresol solutions reveal the existence of an isotropic and anisotropic phase, as well as a biphasic interval. The effect of the applied shear rate is to shift the anisotropic phase to lower concentrations. The anisotropic phase, which is found from 20 wt.‐% polymer concentration, is characterized by the following features: A) Three flow regions, pseudoplastic, Newtonian and pseudoplastic, respectively, are observed in \documentclass{article}\pagestyle{empty}\begin{document}$ \eta - \dot \gamma _{21} $\end{document} plots but not in η* ‐ ω plots, b) “Grainy” and “thread” textures correspond to regions I and II respectively, c) Activation energies of flow are similar to that of the pure solvent, d) Both dynamic viscoelastic functions G′ and G″ scale with frecuency as ω0.75, a dependence already observed in complex liquids, like heterogeneous block copolymers.On the other hand, dynamic viscoelastic measurements performed with isotropic systems allow to determine the entanglement modulus and the associated molecular weight between entanglement couplings, Me0=7830.

Properties of resistive thick films based on powdered Sn0.9Sb0.1O2 and obtained by heat treatment in nitrogen

Powders of the solid solution Sno.9Sb0.102 with a specific surface of 1.7 m2/g were obtained by the method described in [6]. The glasses used as binders had the chemical and physical properties shown in Tables 1 and 2. The specific surface of the glass powders after grinding was 0.8-1 m2/g. We mixed the solid solution and glass with an organic binder (a 3 % solution of ethyl cellulose) in terpineol to obtain pastes. These pastes were then applied by masking to ceramic substrates placed between previously sintered copper contacts. The films were heat-treated in a stream of nitrogen inside a muffle furnace with a hydraulic seal. Temperature in the furnace was raised from room temperature to the maximum (Tma x = 7001000°C) with holds at 140, 400°C, and Tma x over a period of 15 rain. The thickness of the films was 25-30/zm. Their resistance was measured at room temperature, while the temperature coefficient of resistance (TCR) was measured within the interval 25-125°C. Figure 1 shows the dependence of the resistivity of the films on Tma x. It was established that the glass-based films had a porous, poorly sintered structure up to 900°C, regardless of the grade of glass that was used. This is due to the presence of residual finely dispersed carbon formed as a result of thermal degradation (pyrolysis) of the organic binder and not burned up in the inert medium before the softening glass wet the particles of the current-conducting phase. The interaction of the carbon with oxides of tin and antimony leads to the evolution of gaseous reaction products (CO, CO2), which cause the films to foam.

Studies on the Development of Intragastric Floating and Sustained Release Preparation. I. Application of Calcium Silicate as a Floating Carrier.

We prepared an intragastric floating preparation using porous calcium silicate (Florite[○!R] RE, FLR) as a floating carrier, which has floating ability due to the air included in the pores when they are covered with a polymer, it also has a sustained drug release property. Floating granules were prepared by dropping a 5 or 10% (w/v) ethanol solution of hydroxypropylcellulose (HPC) and ethylcellulose (EC) in 4 different concentration ratios while the FLR was being agitated in a beaker. After the mixture was dried in vacuo and sieved, we regarded the granules obtained as primary coated granules (PCG). After drying, the ethanol solution of the polymer was dropped and dried in vacuo again, and sieving was carried out to obtain secondary coated granules (SCG). The floating property and surface and inner structures of PCG and SCG were studies. Further, we prepared PCG and SCG including diclofenac sodium (DS) (DS-PCG, DS-SCG) as a model drug, and the drug release profile from these granules was observed.The floating property of SCG was better than that of PCG. A longer floating time was observed with a higher polymer concentration and a lower HPC composition ratio. It was observed by a scanning electron microscope (SEM) and the pore size distribution that more pores of FLR in SCG were covered with polymer than those in PCG. DS-SCG showed a smaller release rate than DS-PCG. These results suggest that FLR is a useful floating carrier for the development of floating and sustained release preparations.

Dynamic Surface Tension of Aqueous Polymer Solutions, I: Ethyl(hydroxyethyl)cellulose (BERMOCOLL cst-103)

The dynamic surface tension of aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) was measured using the pendant-drop method and digital-image analysis. The EHEC concentrations studied ranged from 3.2·10−5to 0.28% w/w. The time dependence of surface tension was analyzed using a diffusion-kinetics-controlled theory where the adsorption kinetics depended on the fraction of the total surface coverage. For EHEC concentrations ≤10−3% w/w, the isotherms showing surface tension vs log time follow a sigmoidal pattern. Three consecutive kinetic regions exist: the induction region, the surface-coverage region, and the mesophase region. The process of the adsorption of polymer segments is described in terms of relaxation times and the critical points of time, at the onset and at the end of the region of surface coverage. An extremely slow surface equilibration in the mesophase region indicates a progressive ordering of the polymer segments within the surface layer.

Rheological and dynamic light-scattering studies on aqueous solutions of a hydrophobically modified nonionic cellulose ether and its unmodified analog

Dynamic light-scattering (DLS) and oscillatory shear experiments have been carried out on aqueous solutions ofethyl(hydroxyethyl)cellulose (EHEC) and of a hydrophobically modified analogue (HM-EHEC) in the presence of various amounts of sodium dodecyl sulfate (SDS). Both the rheological and the DLS measurements revealed significant polymer-surfactant interaction for the EHEC/SDS and HM-EHEC/SDS systems at surfactant concentrations of 8-10 and 4-5 mm, respectively. The observed rheological and hydrodynamic effects for both systems were found to be strongly dependent upon the level of surfactant addition, with at first an increase and then a decrease in the values of parameters such as the dynamic viscosity, the storage and loss moduli, the slow relaxation time from DLS, and the wave vector dependence of the slow inverse relaxation time. The strength of interaction was considerably stronger in solutions of the hydrophobically modified polymer at moderate surfactant concentrations due to enhanced hydrophobic associations. At higher surfactant concentrations, a breakdown of chain associations occurred. The rheological properties of the hydrophobically modified polymer at moderate surfactant concentrations suggest that the elastic response dominates at higher frequencies. The time correlation data obtained from the DLS experiments revealed, for both systems at all surfactant concentrations, the existence of two relaxation modes, one single exponential at short times followed by a stretched exponential at longer times. The values of the slow relaxation time were constantly found to be several orders of magnitude higher than those of the fast relaxation time, with a maximum value observed for the HM-EHEC/SDS system at a surfactant concentration of about 4 mm. The fast mode was always diffusive, while the slow mode exhibited a stronger and more complex wave vector dependence. Under certain polymer-surfactant conditions, the DLS results at low scattering angles indicated the formation of large clusters.

Induced circular dichroism as a probe of handedness in chiral nematic polymer solutions

Abstract Achiral dyes in isotropic (acetyl)(ethyl)cellulose (AEC) solutions display no induced CD signals irrespective of acetyl content, polymer concentration or dye content. When dissolved in anisotropic AEC solutions, the dye molecules show strong induced CD bands that disappear when the phases are heated above the anisotropic/isotropic phase transition temperature. The liquid crystal induced circular dichroism (LCICD) spectra for the dyes in a series of well-characterized AEC mesophases, whose handedness depends on solvent and acetyl content, reveal that the sign of the LCICD signal is determined by the supramolecular structural features of the host matrices. Thus, acridine orange (AO) dissolved in a left-handed liquid crystalline AEC solution displays a negative LCICD whereas a positive LCICD was observed when the AO is dissolved in a right-handed AEC mesophase. The sign and intensity of the LCICD signals change with acetyl degree of substitution, solvent and temperature. In all cases, changes in sig...

Preparation and Characterization of Ethylcellulose-Walled Theophylline Microcapsules Using the Emulsion-Solvent Evaporation Technique

AbstractEthylcellulose microcapsules containing theophylline are prepared by emulsification of a organic ethylcellulose solution in a oil phase containing a surfactant. The preparation is based on dispersion of acetone containing the drug in liquid paraffin. Tween 80 was used as a dispersing agent. Good reproducibility in microcapsule preparation was observed. The microcapsules obtained were uniform and free-flowing particles. The type of the stirring-manner (propella – and magnet – stirring), and the drug to polymer ratios have an important influence on the in vitro dissolution and release of theophylline from microcapsules.

大腸デリバリー技術 時間制御型大腸デリバリーカプセル

We have tried to exploit a time-controlled drug release system, a colon delivery capsule made of ethylcellulose (EC). Our colon delivery capsule is consisting of four parts, capsule body, cap, swellable substance and drug container. The cap, body and drug container were made of EC, which was water-insoluble polymer. At the bottom of the body, four micropores were made. The cap has different thickness and as adhered to the capsule body with concentrated EC solution. The drug release mechanism from the capsule was as follows. AL first, as the gastrointestinal fluid penetrates through these micropores, the swellable substance such as low substituted hydroxypropylcellulose(L-HPC) swells gradually. When the cap cannot endure the swelling pressure, the cap disintegrates and the drug in the container is released from the capsule. This release time of the drug from the capsule, namely the lag-time, is utilized for the delivery of drug to the colon. The lag-time was evaluated both in vitro and in vivo experiments using fluorescein as a model drug. In the case of an in vitro experiment, changing the cap thickness could control the release time of the drug. A good correlationship was obtained between the EC cap thickness and the release time of the drug. In the in vivo experiment, we administered these kinds of capsules having different cap thickness were administered to fasted beagle dogs. As an index of the release time of the drug from the capsule, the peak time(Tmax) at which plasma fluorescein level reached to its maximum level was determined. There was a good correlationship between the mean Tmax and the cap thickness. Therefore, we may state that this time-controlled release capsule will be useful for the colon delivery of drugs.

Effect of degree of acetylation and solvent on the chiroptical properties of lyotropic (acetyl) (ethyl) cellulose solutions

Abstract(Acetyl) (ethyl) cellulose (AEC) polymers with an ethyl degree of substitution (DS) of 2.5 and acetyl DS ranging from 0 to 0.5 dissolve readily in a wide range of organic solvents and form chiral nematic liquid crystalline phases in concentrated solution. The chiroptical properties of these liquid crystals are strongly influenced by the acetyl content and solvent. In dichloromethane, dibromomethane, chloroform, bromoform, m‐cresol, acetic acid, and aqueous phenol, the AEC lyotropic mesophases all show a handedness inversion as the acetyl DS of the polymers is increased, changing from left‐ to right‐handed supermolecular helicoidal structures. The temperature dependence of the pitch for these mesophases is also reversed from negative to positive with increasing acetyl DS in all the above solvents except aqueous phenol, in which the corresponding AEC mesophases change from positive to negative. The optical microscopic, optical diffraction, and ORD evidence provide a unique indication that the reversal of the handedness and temperature dependence for the AEC mesophases occurs at a compensated degree of acetylation, DA*. The corresponding compensated mesophases show an infinite pitch and behave optically like nematic mesophases. The value of the DA* is dependent on solvent. In dichloroacetic acid, AEC liquid crystals remain right‐handed, independent of the acetyl DS. At given concentration and temperature, the long pitch samples flow much more readily than short pitch samples. © 1994 John Wiley &amp; Sons, Inc.

Effect of addition of cellulose powder on the viscometric behavior of liquid crystalline solutions of ethyl cellulose in m‐cresol

AbstractSteady‐state shear viscosity for the liquid crystalline ethyl cellulose solution filled with cellulose powders was determined using a cone‐plate‐type viscometer and the effects of cellulose powder content, powder aspect ratio and temperature on the viscometric behavior and phase transformation were discussed. The addition of powder increased the viscosity and decreased the activation energy (Ea) for flow, but did not affect the phase transformation. The viscosity and Ea depended on the aspect ratio; with greater aspect ratio, the viscosity enhancement was accelerated and Ea as well as the decrease in Ea with powder content increased. The phase transformation did not depend on the aspect ratio, the dependences of viscosity and of Ea on powder content depended on the solution phase; the dependences for the anisotropic phase were smaller than those for the isotropic one. The findings appeared to originate from the alignments of powders and rod‐like molecules.

Porosity-Controlled Ethylcellulose Film Coating. V. Mechanism of Drug Release from Beads Coated with Porous Ethylcellulose Film.

The porous ethylcellulose (EC) film-coating technique was applied to prepare the film-coated (so-called capsule-type) controlled release dosage form of phenylpropanolamine hydrochloride (PPA), which was used as a highly water-soluble model drug. To prepare EC film-coated beads with various film-porosities, the PPA-loaded uncoated beads were spray-coated with an aqueous ethanolic or ethanolic solution of EC, and their drug release behaviors or drug release mechanisms were investigated. Although the amount of coating of the beads was equal, the PPA release rate differed according to the ethanolic concentration in the coating solution, that is, the lower the ethanolic concentration, the faster the release rate. The release profiles were normalized using a reduced time method to compare the profiles of different release rates. It was found that the profiles were well superimposed on the same curve, suggesting that the drug release obeyed the same mechanism. To examine the mechanism of drug release from the EC film-coated beads of PPA, drug release behaviors were investigated under the condition of various osmotic pressure differences. The drug release rate was decreased by decreasing the osmotic pressure difference. The contribution of an osmotic pumping to the drug release was estimated for the EC film-coated beads with different coating porosities. The driving force for drug release from the porous EC film-coated beads was found to be mainly an osmotic pumping mechanism, irrespective of film porosity.

Porosity-Controlled Ethylcellulose Film Coating. III. Application of Porous Ethylcellulose Film Coating to Capsule-Type Controlled Release Preparation of Theophylline.

Porous ethylcellulose (EC) film coating technique was used in preparing a capsule-type controlled release dosage form, in which theophylline (TP) was used as a poorly water-soluble model drug. The TP-loaded uncoated beads were spray-coated with an aqueous ethanolic or ethanolic EC solution, and the drug release characteristics and productivity of each product were examined. When the aqueous ethanol was used as the solvent of the coating solution, a large number of micropores were formed in the coating, and the porosity of coating and drug release rate could be controlled by altering the ethanolic concentration in the coating solution. In addition, few agglomerates were produced in the coating process, even though there was no anti-agglomeration agent in the coating solution. The drug release rate from the coated beads could be changed by film porosity as well as film thickness. Superposition analysis revealed that the EC-coated beads with different film porosities or different coating levels had the same drug release mechanism. It was further found that the drug release behavior of the porous EC film-coated beads was not affected by any simulated physiological conditions such as pH, surface tension, ionic strength or paddle rotation speed, indicating that in vivo drug release should not be affected by such physiological conditions in the gastrointestinal tract.

Neck clipping の困難な“小”脳動脈瘤の治療法

Cerebral aneurysms are difficult to treat by neck clipping if their size is too small, or if they are fusiform or have branches from their dome. What therapeutic methods should we select for such cases? If wrapping or coating is to be done, what material should be selected? In recent years, complications such as granuloma or optochiasmal arachnoiditis following wrapping with gauze have been reported by several investigators. We encountered a case in which a small anterior cerebral artery aneurysm and an infundibular dilatation later enlarged and hemorrhaged when they were left untreated. Recognizing the necessity of treatment of these types of small aneurysms, we have been developing and assessing new wrapping and coating materials.Of the 620 patients who underwent a direct operation on cerebral aneurysms, 10.8% received wrapping or coating independently or after clipping. The reason for the use of wrapping or coating was the presence of a broad neck in 56.7% and small aneurysms in 22.4%.Histologically, the tissue wrapped with gauze showed infiltration of inflammatory cells, accompanied by fragile granulation. Bemsheets were found to form a firm reinforcing wall as a result of a fibrous tissue reaction with little cell infiltration. Thus, Bemsheets appear to be an excellent wrapping material.Conventional coating materials such as cyanoacrylate adhesives have been reported to involve problems such as vasotoxicity, late thrombosis, neurotoxicity and deterioration in vivo. We have developed an ethyl acetate solution of ethyl cellulose as a new coating material, and named it“liquid cellulose.”It has a pH of 7-8, a membrane-forming time of 60 seconds, and distensibility of 2-24%.These physical properties make this material easy to manipulate. It is also very tough (490kg/cm2) and flexible and has a viscosity of 1000-2000 cp, which varies depending on the cellulose consentration and the degree of polymerization.Scanning electron microscopy of this“liquid cellulose”revealed a multiple laminar structure, suggesting formation of flexible and strong walls.The development and assessment of new wrapping and coating materials for the treatment ofsmall cerebral aneurysms is very important. Bemsheets and“liquid cellulose”seem to be excellent wrapping and coating materials.