Polyvinyl Acetate Dispersion Research Articles

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.

Compression of pellets coated with various aqueous polymer dispersions

Pellets coated with a new aqueous polyvinyl acetate dispersion, Kollicoat ® SR 30 D, could be compressed into tablets without rupture of the coating providing unchanged release profiles. In contrast, the compression of pellets coated with the ethylcellulose dispersion, Aquacoat ® ECD 30, resulted in rupture of the coating and an increase in drug release. Plasticizer-free Kollicoat ® SR coatings were too brittle and ruptured during compression. The addition of only 10% w/w triethyl citrate as plasticizer improved the flexibility of the films significantly and allowed compaction of the pellets. The drug release was almost independent of the compression force and the pellet content of the tablets. The inclusion of various tabletting excipients slightly affected the drug release, primarily because of a different disintegration rate of the tablets. The core size of the starting pellets had no influence on the drug release. Pellets coated with the enteric polymer dispersion Kollicoat ® 30 D MAE 30 DP [poly(methacrylic acid, ethyl acrylate) 1:1] lost their enteric properties after compression because of the brittle properties of this enteric polymer. Coating of pellets with a mixture of Kollicoat ® MAE 30 DP and Kollicoat ® EMM 30 D [poly(ethyl acrylate, methyl methacrylate) 2:1] at a ratio of 70/30 and compaction of the pellets resulted in sufficient enteric properties.

PH-independent release of a basic drug from pellets coated with the extended release polymer dispersion Kollicoat ® SR 30 D and the enteric polymer dispersion Kollicoat ® MAE 30 DP

The objective of this study was to obtain pH-independent release profiles from coated pellets containing drugs with pH-dependent solubility. pH-independent release of the basic model drug verapamil HCl was achieved by coating with a combination of the neutral polymer dispersions Kollicoat ® SR 30 D (aqueous dispersion of polyvinyl acetate) and the enteric polymer dispersion Kollicoat ® MAE 30 DP (aqueous dispersion of methacrylic acid and ethyl acrylate copolymer; methacrylic acid copolymer type C). The two polymers where applied either as separate layers (enteric polymer+extended release polymer or vice versa) or as a polymer blend. A careful balance of the ratios of the polymers allowed the achievement of a pH-independent release. Higher amounts of the enteric polymer in the polymer blend resulted in a reversal of the pH-dependency, e.g. a faster release at pH 6.8 than in 0.1 N HCl.

Gas-Phase Fluorination of Films and Coatings Based on Polyvinyl Acetate Dispersions with Sulphur Tetrafluoride

Gas-Phase Fluorination of Films and Coatings Based on Polyvinyl Acetate Dispersions with Sulphur Tetrafluoride

Wettability of refractory fibers using water-soluble binders

The wettability of refractory glass fibers of an aluminosilicate composition by watersoluble binders (water glass, silica sol, or a polyvinyl acetate dispersion) has been studied; the critical surface tension of the fibers and the thermodynamic work of adhesion has been determined. It is established that the PVAD and silica sol are almost identical wetting agents for glass fibers and are slightly better than water glass. A direct connection has been established between the adhesion of the binder to the fibers and the bend strength of the thermal-insulating products.

Effect of the type of binding material on the properties of refractory glass-fiber heat-insulation products

The effect of binders (water glass, silica sol, chromium-aluminophosphate binder, bentonite, and polyvinyl-acetate dispersion) on the basic properties of thermal-insulation glass-fiber refractory articles has been studied.

The rheological properties of concentrated polymer dispersions

Abstract Measurements of viscosity have been obtained upon homogenized and unhomogenized polyvinyl acetate dispersions of differing sizes and size distributions. The measurements were obtained at shear rates ranging from 1 sec−1 to 2600 sec−1 for dispersion volume fractions of approximately 0.2 up to 0.5. The electrolyte content of the dispersions was held constant at 0.017 M. The data were analyzed on the basis of a three-component Eyring model for viscosity and the associated molecular parameters were obtained. The results obtained for the unhomogenized dispersions indicate the considerable errors in the derived values which may arise owing to the presence of coarse agglomerates of particles. The data for the homogenized dispersions illustrate a consistent trend in the derived parameters, showing that the relaxation time of the first non-Newtonian component is independent of the concentration and increases with increasing particle size. The relaxation time of the second non-Newtonian component exhibits a strong concentration dependence, decreasing rapidly with decreasing concentration and decreasing with increasing particle size. The Newtonian component ηo — η∞ and ηo — ηo for the homogenized dispersions show a linear dependence on concentration as suggested by the Mooney equation log e n re1 = k 1 k 2 φ/ (1 − k 2 φ) . The values of the associated particle-crowding factor k2 for the three parameters indicate that the second non-Newtonian flow unit which predominates at low rates of shear is associated with very marked particle interaction.

Effects of Plastic and Acrylate Polymers on the Release Profile of Ambroxol Hydrochloride Controlled Release Pellets

The effects of Ammonio Methacrylate copolymer dispersion (Eudragit® NE 30 D) and Polyvinyl Acetate dispersion (Kollicoat® SR 30 D) are compared on the in vitro release of Ambroxol Hydrochloride from coated pellets in the current study. The nuclei pellets were manufactured by Extrusion-Spheronization with the drug, microcrystalline cellulose, lactose, maize starch, and hydroxypropyl methylcellulose followed by fluid bed coating. Dissolution study of coated pellets was performed with USP Type-II apparatus in acidic (0.1N HCl for 1 h) and buffer (phosphate buffer, pH 6.8 for 11 h) media to simulate gastrointestinal environment. The release profile of drug from two types of polymers were distinct and drug release was sustained longer by Polyvinyl Acetate film than Acrylate polymer. Key words: Aqueous coating, Eudragit® NE 30D, Kollicoat® SR 30D, release kinetics, pellets, extrusion-spheronization doi: 10.3329/dujps.v7i2.2176 Dhaka Univ. J. Pharm. Sci. 7(2): 181-186, 2008 (December)

Formulation and Evaluation of Release Kinetics of Diltiazem Hydrochloride from Kollicoat SR 30 D Coated Pellets Prepared by Air Suspension Technique

The purpose of the present study is to investigate the effect of polyvinyl acetate on the release kinetics of diltiazem hydrochloride from coated pellets prepared by solution and suspension layering technique. Kollicoat SR 30 D, an aqueous dispersion of polyvinyl acetate with different weight ratios was chosen to sustain the release of the drug. Drug was loaded with hydroxypropyl methyl cellulose on nonpareil seeds then coated with the Kollicoat SR 30 D. In vitro dissolution studies were carried out using USP dissolution apparatus Type-2. No significant difference was found in drug release from uncoated pellets and the pellets coated with 5% polymer load. With 10% polymer load, the initial release was minimized but from 2nd hour the release was quick-tempered. Better sustaining effect was found from 15- 20% polymer loaded pellets. The mean dissolution time was 2.5h and 4h while the polymer load was 15% and 20% respectively. Also these two cases 80% drug was released at 6h and 9h respectively. The physical parameters of the prepared pellets were also compared in this study. The release of drug from the coated pellets appeared to follow Higuchi's release kinetics.Key words: Diltiazem, Pellets, Kollicoat SR 30 D, Aqueous coating, Physical parameters, Release kinetics.DOI = 10.3329/bjsir.v43i3.1147Bangladesh J. Sci. Ind. Res. 43(3), 321-332, 2008

Development of Salbutamol Sulphate Sustained Release Pellets Using Acrylic Polymer and Polyvinyl Acetate Polymer and Evaluation of <i>In vitro</i> Release Kinetics

The nuclei of sustained-release pellets of salbutamol sulphate were prepared using extrusionspheronization technique followed by coating with the aqueous dispersion of methacrylic acid esters (Eudragit RS® 30 D) and commercial aqueous polyvinyl acetate dispersion (30% dispersion) (Kollicoat SR® 30 D). The coating polymers were applied to obtain a theoretical polymer load of 5%, 10%, 15%, 20% & 25 %( w/w) on the nuclei. Invitro dissolution studies of the coated pellets were performed in a USP paddle apparatus (type-2). Dissolution media was distilled water (500 ml), paddle speed was 50 rpm and it was preformed for 8 hours at 37°C (±0.5°C) temperature. Scanning Electron Micrographs (SEMs) of the nuclei & coated pellets were taken to study their surface morphology. The kinetics of the dissolution process was determined by analyzing the dissolution data using zeroorder, first order, Higuchi and Korsmeyer equations. The kinetic modeling of the dissolution profiles revealed that drug release mechanism ranged from diffusion controlled or Fickian transport to anomalous type or non-Fickian transport. T50% (MDT) and T90% values were calculated for each formulation. The higher MDT values were obtained with Eudragit® RS 30D where as Kollicoat® SR 30D showed comparatively low MDT values. MDT values were also increased with increasing polymer load on the nuclei. Key words: Salbutamol sulphate; Pellet; Aqueous dispersion; Eudragit® RS 30 D; Kollicoat® SR 30D; Extrusion spheronization; MDT. DOI: http://dx.doi.org/10.3329/dujps.v9i2.7895 Dhaka Univ. J. Pharm. Sci. 9(2): 109-118, 2010 (December)

The mechanical stability of colloidal dispersions

The coagulation of an aqueous polyvinyl acetate dispersion has been studied under steady shear. This type of dispersion was stable for three years in storage but coagulated in a few seconds when intense shear was applied. Most of the tests were carried out under conditions of laminar flow. Tests were also made in the absence and presence of air-liquid interface, and no difference was detected. Under laminar shear the coagulation was studied (1) by varying the rate of shear and (2) under constant rate of shear. The exact cause of mechanical coagulation could not be determined. Some of the factors are pointed out which may explain the behavior under liquid shear.

Dynamic mechanical properties of polyvinyl acetate

The real and imaginary components of the complex compliance have been measured between 30 and 5100 cycles/sec. at nine temperatures between 50°C. and 90°C. on an unfractionated sample of polyvinyl acetate ( M n = 140,000, M w = 420,000). The results superpose by the method of reduced variables to give composite curves covering the transition from rubberlike to glasslike consistency as a function of frequency at 75°C. From these, the reduced curves for the real and imaginary parts of the complex shear modulus, and the real part of the complex viscosity, have been calculated. Earlier data of Mead and Fuoss on dielectric dispersion and dielectric loss of polyvinyl acetate have been reduced to 75°C. in the same manner, and the mechanical and electrical reduction factors are found to be identical. The apparent activation energy for mechanical and electrical relaxation increases sharply with decreasing temperature, as observed for other polymers. Distribution functions of mechanical relaxation and retardation times, and of electrical relaxation times, have been calculated from both real and imaginary components of modulus, compliance, and dielectric constant, respectively. The results of the approximation formulas of Williams and Ferry and of Schwarzl and Staverman are found to be closely similar. The electrical relaxation spectrum is somewhat flatter, and lies at shorter times, than the mechanical retardation spectrum.

The use of polyvinyl alcohol and its derivatives as microscopical mounting media. Part II. Hydrocarbon-miscible mounting media.

SYNOPSISA mounting medium with a refractive index of 1·474 had been developed from a 23 p.c. dispersion of polyvinyl acetate in “cellosolve” plasticized with 13 p.c. of diamyl phthalate. When heated the medium hardened in 2–3 days to a stable transparent film which did not cause stain‐fading in test mounts stained with either Ehrlich's acid alum haematoxylineosin B or with Mallory's acid fuchsin‐orange G‐aniline blue and exposed for 6 weeks to heat, artificial, or natural lighting.