ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
The elongation of polyvinyl alcohol and of formalized polyvinyl alcohol films under constant load for a wide range of conditions of temperature and humidity seems to be affected predominantly by the diffusion of water molecules into these polymeric films, as these films have many water-sensitive bonds. In order to obtain a perspective of the diffusion mechanism of water molecules into these polymer films, the theoretical analysis of creep curves is here worked out. Since the diffusion is a time-dependent, non-Fickian process, the time dependence of the diffusion coefficient is considered into our theoretical treatment. It is also assumed that the elongation is caused only by the breaking of hydrogen bonds due to the absorption of water molecules in amorphous regions of the polymer film.To evaluate theoretical equations for the creep curves in accordance with a simple Voigt model, the parameter α for the rate of diffusion is conveniently substituted for by K, the parameter for the rate of elongation. Experiments were performed at temperatures from 20 to 50°C. at 60% R. H., and also at different relative humidities ranging from 40 to 80% at a constant temperature of 30°C. A series of creep curves for PVA and PVF, the latter having a degree of formal substitution ranging from 6% to 42.5% were obtained.In analyzing the observed creep curves by the present theoretical treatment, we can easily compute the values of K through application of the condition for the characteristic inflection point of each curve, i.e., d2γ/dt2 = 0. By use of the values of K thus obtained and by application of the theory of absolute reaction rates, the activation energy and entropy for the diffusion process of water molecules are duly determined. The values thus obtained are also compared with those calculated by Hauser and McLaren. The activation energy and entropy are highest and lowest, respectively for PVF (6%); this is made adequately explicable by the fact that the proportion of amorphous polymer in these films is found to be maximum when the degree of formalization is between 10 and 20%.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1959.070020411
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