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Viscoelasticity of ABS samples differing in thermal history
Author(s) -
Booij H. C.,
Palmen J. H. M.
Publication year - 1978
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760181008
Subject(s) - viscoelasticity , materials science , thermodynamics , stress relaxation , annealing (glass) , thermal , relaxation (psychology) , cooling curve , composite material , creep , physics , psychology , social psychology
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 t r . The value of t r 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, t a , 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 t r and t a at temperatures below T g −15°C. In slowly cooled samples t r 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 t a , but remains substantial up to t a values much longer than the total cooling time.