Aqueous Hydroxypropyl Methylcellulose Research Articles

Transition of viscous fingering patterns in polymer solutions

Viscous fingering patterns of aqueous hydroxypropyl methyl cellulose (HPMC) solutions pushed by air in the Hele–Shaw cell were observed as a function of isopropyl alcohol content under a constant pressure of 15 cm H2O. A morphological transition from side branching patterns to tip splitting ones with increasing isopropyl alcohol content, accompanied with a decrease in surface tension and an increase in viscosity is found. The observed morphology transition was correlated with the dimension of the fingering pattern, as well as the average tip velocity in the fingering.

The mechanical and moisture permeability properties of aqueous-based hydroxypropyl methylcellulose coating systems plasticized with polyethylene glycol

The effects of polyethylene glycols (PEG 400, 1500 and 4000) used as plasticizer on the moisture permeability and mechanical properties of aqueous hydroxypropyl methylcellulose (HPMC) films were evaluated with free films. The free films were prepared by using a pneumatic spraying technique similar to that used in fluidized-bed coaters. There was a clear relationship between some physical film properties and the molecular weights and concentrations of the PEGs used as plasticizer. Over the range of concentrations tested, the moisture permeability of the films decreased slightly as compared to unplasticized control films with increasing molecular weight of the plasticizer. The mechanical strength of the films was shown to be more dependent on the concentration than on the molecular weight of the PEGs, while the ductility of the films was mainly dependent on the molecular weight of the PEG. The addition of PEG at a concentration of 10% resulted in relatively hard and strong films with a moderate elongation (ductility), especially when lower molecular weight plasticizers (PEG 400 or 1500) were used. As regards permeability to moisture and mechanical properties, the addition of PEG at a concentration in the range of 10–20% of the polymer weight seems to be beneficial for aqueous-based HPMC film coats.

Effects of polymer adsorption and desorption on rheological properties of silica suspensions

Shear stresses and dynamic moduli of silica suspensions in aqueous hydroxypropyl methyl cellulose (HPMC) solutions were measured by using a cone-plate geometry as functions of the concentrations of silica, HPMC, isopropyl alcohol, acetic acid and pyridine. Isopropyl alcohol and pyridine behaved as displacers and they cause desorption of HPMC from the silica surfaces. The amounts of HPMC adsorbed on the silica surfaces decrease with an increase in the displacer concentration. In plots of steady state shear stress against shear rate, there was a shear rate of about 0.1 s −1 due to aggregation of the silica particles and this did not disappear on addition of isopropyl alcohol or acetic acid. However, the silica suspensions with pyridine must show some stress responses, although these may be outside the measurement range for the instrument. Pyridine increases the pH in the dispersion, leading to stable and unaggregated silica particles. By adding isopropyl alcohol to the silica suspensions, the storage modulus decreases with the amount of HPMC desorbed from the silica surfaces. The larger amounts of HPMC desorbed resulted in no second plateau in the dynamic moduli, showing the weaker aggregated structures in the silica suspensions. In contrast, pyridine had no detectable effect on the dynamic moduli of the silica suspensions.

Plasticization of aqueous poly(vinyl alcohol) and hydroxypropyl methylcellulose with polyethylene glycols and glycerol

The plasticization of aqueous hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) with poly(ethylene glycols) (PEGs) with various molecular weights and with glycerol has been investigated. The plasticizing efficiency in the case of HPMC was: PEG200 > PEG400 > GLYCEROL > PEG6000 and for PVA: GLYCEROL > PEG200 > PEG400 > PEG6000. The plasticizer efficiency rating was explained with the partial solubility parameters of the polymers and the plasticizers in terms of the propensity of each polymer-plasticizer pair to set up polar and hydrogen-bonding interactions. Phase separation of the plasticizers occurred above a critical concentration which, in the case of PEGs, was inversely proportional to molecular weight. Phase separation of the plasticizer was shown to be responsible for deterioration in the plasticizing efficiency.

Phase separation and polymer interactions in aqueous poly(vinyl alcohol)/hydroxypropyl methylcellulose blends

This paper discusses the compatibility of aqueous hydroxypropyl methylcellulose (HPMC)/poly(vinyl alcohol) (PVA) blended systems. Dynamic mechanical analysis and differential scanning calorimetry have provided clear evidence of two phases. Each phase precluded almost completely the other component. The HPMC-rich phase was amorphous with a constant T g while the PVA-rich phase showed a limited level of crystallinity and a constant T g for the amorphous part. Fourier-transform infra-red studies indicated hydrogen-bonding interactions involving the carbonyl and hydroxyl groups of like molecules but no detectable interactions between HPMC and PVA. A new hydrogen-bonding environment of the hydroxyls was observed in the blended system but was not capable of inducing any compatibility. The gross incompatibility was successfully predicted by the total solubility parameters of the two polymers and attributed to significant differences in the polar and hydrogen-bonding contributions. Surface energy analysis corroborated the inability of the two chains to participate in acid-base interactions between unlike molecules due to significant discrepancies in their Lewis acid-base characteristics. Finally, determination of the free energy of polymer-polymer interaction in water allowed approximate calculation of the Flory-Huggins parameters of aqueous PVA and HPMC systems.

Effect of Storage on the Properties of Acetylsalicylic acid Tablets Coated with Aqueous Hydroxypropyl Methyl-Cellulose Dispersion

AbstractThe objective of this study was to investigate whether the properties of acetylsalicylic acid tablets coated with aqueous hydroxypropyl methylcellulose dispersion using glycerol or polyethylene glycol 6000 as plasticizer change during storage at 25° or 40°C. Titanium dioxide was used as pigment. The tablets were coated in a fluid bed apparatus. The disintegration time and the release of acetylsalicylic acid during two hours were determined for both uncoated and coated tablets immediately after their preparation and after different storage periods.When the tablets were stored at room temperature (25°C) the coat protected the core efficiently against changes in the measured parameters as compared with uncoated tablets. However, at higher temperature (40°C) some unfavorable phenomena occurred in the coat and after storage of 48 months, the disintegration time was longer and the dissolution of acetylsalicylic acid slower than from uncoated tablets. Polyethylene glycol was found to be a better protecti...

Photodepolymerization of hydroxypropylmethylcellulose

AbstractThe light‐induced degradation of aqueous hydroxypropylmethylcellulose (HPMC; D.S. 1.9) solutions has been investigated under a variety of conditions. The HPMC was sensitized to short‐wavelength radiation (<500 nm) by the addition of sodium nitrite, the degradation being accompanied by increased acidity and the generation of oxides of nitrogen. Addition of eosin dye increased the sensitivity to visible light (>500 nm), and the effect was considerably more pronounced when strong electron donors were added. Analysis of the shear–viscosity relationship of the solutions, during the degradation, indicated that both chain disentanglement and chain scission occurred but that the primary process was the depolymerization of the cellulose chain. It is proposed that both the dye‐ and nitrite‐induced depolymerizations are a consequence of peroxide attack on the β‐glucosidic ether link. The results indicate that, in the case of sodium nitrite addition, the peroxide was generated by the aqueous photolytic decomposition of the nitrite ion. The peroxide formation in the eosin—TEA system was a consequence of leuco‐dye production, under the influence of the light, followed by the reduction of traces of dissolved oxygen by this activated dye.