ISSN:
0021-8995
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
,
Physik
Notizen:
As part of a continuing study of nonisothermal rheology (meaning the simultaneous application of strain and temperature changes), we here consider the behavior of polystyrene near the glass transition temperature Tg. In particular, we measured the increase of the apparent Tg as the cooling rate is increased from 0.003 to 4.5°C/sec. This change (up to 16°C increase) has both practical and theoretical implications. For enhancing the mechanical properties of a glassy product, one desires maximum orientation (stress) just prior to quenching; the optimum deformation/temperature strategy for maximizing stress is affected by the level of Tg. By using a nonisothermal strategy we were able to produce higher frozen-in orientations, and thus higher mechanical properties, than have been previously reported. For a theoretical understanding of the rubbery state just prior to quenching, we used the generalized time-temperature superposition of our prior work; we found that a modified shift factor of the form aT(T,TRg), where TRg refers to a rate-dependent Tg, gives an improved fit to data but is not by itself adequate.
Zusätzliches Material:
14 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/app.1980.070250405
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