ISSN:
0032-3888
Schlagwort(e):
Chemistry
;
Chemical Engineering
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
,
Physik
Notizen:
An important parameter in the various molding techniques used in polymer processing is the rate of cooling the object. The effect of the thermal history on the linear viscoelastic properties was studied, mainly by means of stress relaxation experiments on ABS samples in which the influence of other process variables was eliminated. In agreement with recent literature data, it appeared that the time dependence of the stress can be represented by a universal formula, provided that no perceptible change in temperature or relaxation of volume takes place during the experiment. The position of the momentary relaxation curve along the time scale can therefore be described by one characteristic mechanical relaxation time tr. The value of tr is affected by the temperature T, but even more by the thermal history, i.e., by the rate of cooling, q, and the annealing time, ta, at the measuring temperature previous to recording of the relaxation curve. In the case of very rapidly quenched samples, exact proportionality was found to exist between tr and ta at temperatures below Tg -15°C. In slowly cooled samples tr can be longer by a factor of ten than in quenched samples, at the same T and at annealing times of about 1 h. The difference decreases with increasing ta, but remains substantial up to ta values much longer than the total cooling time.
Zusätzliches Material:
7 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pen.760181008
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