ISSN:
0032-3888
Schlagwort(e):
Chemistry
;
Chemical Engineering
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
,
Physik
Notizen:
At a fixed vapor pressure p of the penetrant and constant temperature of the experiment, the sorption S = c/p or concentration c of the ethylacetate vapor in the uniaxially strained low density polyethylene (LDPE) increases most rapidly at low strains. If, however, on the basis of strain relaxation one separates the total strain ∊ into an elastic ∊e, and a plastic ∊pl, deformation, one obtains an almost linear increase of the concentration c or sorption S of the sorbate with elastic strain ∊e. The separation of ∊ = ∊e + ∊pl depends very much on the time th the sample is kept elongated and the vapor pressure p of the sorbate. The elastic component decreases and the complementary plastic fraction increases with th and p. An almost stationary state is reached after th of about 1/2 h. The calculation of the diffusion coefficient Ds1 from the first sorption immediately after the stretching is affected by this slow adjustment in the interval 0 ≤ th ≤ ½h and shows a pseudo maximum at a strain of ∊∼ = 10 percent. The first desorption experiment and all the later sorptions and desorptions yield the same DD = DS 〈 DS1 that is the correctly calculated diffusion coefficient D. The coefficient D decreases with the strain ∊ or ∊e in contrast with the expected increase of Da of the amorphous component. Such an increase of Da is expected as a consequence of the fractional free volume (FFV) increase caused by the elongation. According to the FFV concept, a decrease of the measured apparent diffusion coefficient D = ψDa requires that with increasing ∊, the tortuosity factor ψ decreases faster than the increase in Da.
Zusätzliches Material:
10 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pen.760231308
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