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The Effect of Physical Aging on the Dissolution Rate of Anionic Polyelectrolytes (1990)

Sinko, Christopher M. ; Yee, Albert F. ; Amidon, Gordon L.

Springer

Pharmaceutical research 7 (1990), S. 648-653

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ISSN: 1573-904X

Keywords: physical aging ; dissolution ; enteric coating ; creep compliance ; hydroxypropyl methylcellulose phthalate

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract The effect of physical aging on the dissolution and mechanical properties of hydroxypropyl methyl-cellulose phthalate (HPMCP) was investigated. Dissolution rate measurements were performed on films which, initially above the glass transition temperature, T g, were quenched to a sub-T g storage temperature, aged at that temperature for a period of time and then quenched again to 25°C. Within the time scale of observation, reductions in the dissolution rate to a limiting value were observed. HPMCP was also found to age in the same storage temperature range as determined by a creep compliance technique. These mechanical results indicate a change in glass structure and show that a limiting density was approached. Parallel changes were observed in the dissolution rate studies suggest that dissolution rate is governed in part by glass density. Therefore, mechanical changes of glassy films can yield pharmaceutically relevant information about the extent of physical aging and serve as an indicator of the effect of aging on dissolution rate.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1015882631082

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Effect of cyclic stress on enthalpy relaxation in polycarbonate (1992)

Liu, Liang B. ; Yee, Albert F. ; Gidley, David W.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 221-230

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ISSN: 0887-6266

Keywords: polycarbonate, cyclic stress and aging of ; differential scanning calorimetry (DSC) of polycarbonate under cyclic stress ; craze initiation and fatigue in glassy polymers ; glassy initiation and fatigue in glassy polymers ; glassy polymers, stress and enthalpy relaxation in ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Possible effects of cyclic stress on physical aging in polycarbonate were investigated using differential scanning calorimetry (DSC) measurements. When the enthalpy overshoot by DSC of specimens of different previous thermophysical aging histories is measured as a function of the cyclic stress amplitudes, two characteristic regimes are observed. By correlating with optical microscopic observations, these regimes are identified as the incubation and crazing stages (denoted regimes I and II, respectively). The enthalpy relaxation behavior in Regime I is similar to thermophysical aging, indicating that the glassy structure as a whole is initially shifted to one where molecular mobility is retarded by relatively low amplitude cyclic stress. A strong interaction is also seen between the enthalpy overshoot and previous physical aging. That is, the more the material is previously aged, and the shorter the incubation period, the longer the crazing region is. As a result, brittle failure occurs over a wider load range compared with less aged specimens.

Additional Material: 10 Ill.