ISSN:
0022-3832
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A detailed study has been made of the rate of take-up of vapors of methylene chloride and acetone by thin films of cellulose acetate (37.9% acetyl) as a function of vapor pressure, film thickness, and temperature. It was found that the method of film preparation and conditioning greatly influenced the kinetics of the take-up. Films, which were not completely dry, exhibit a much faster rate of take-up than dry films. Dry films could he obtained by either long treatment in a vacuum oven, or by water leaching followed by vacuum drying for five days. In either case, identical kinetic results are obtained. The mercury cast films used in this work give reproducible results and show a much slower rate of take-up than a comparable glass cast film.It was found that there was no fundamental difference in the rate of take-up for the vapors of methylene chloride and acetone, although in the liquid state the former is a limited swelling agent, while the latter is a solvent. For both these yapors there is a characteristic pressure above which several anomalies appear, which make a complete quantitative explanation of the data rather difficult. The most important of these anomalies is that, if one plots the amount of vapor taken up as a function of time, an inversion of slope is observed. This inversian is very marked and is a function of film thickness. Another anomaly that appears is that the absolute amount of vapor sorbed for thinner films is greater than that for thicker films for an appreciable time interval. The effect of temperature is complex. Above the pressures where the inversion of a slope occurs, the rate is lower a t higher temperatures for a considerable range of the sorption. These effects cannot be explained on the basis of a generalized diffusion equation with the boundary conditions which have been considered so far, i.e., assuming that the outer film surface is always in equilibrium with the vapor.
Zusätzliches Material:
11 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1951.120060406
Permalink
