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Bulk moduli from physical aging and stress relaxation data
Author(s) -
Kubát M. J.,
Vernel J.,
Rychwalski R. W.,
Kubát J.
Publication year - 1998
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.10296
Subject(s) - materials science , enthalpy , thermodynamics , volume (thermodynamics) , polystyrene , stress (linguistics) , relaxation (psychology) , polyethylene , stress relaxation , modulus , moduli , composite material , polymer , creep , physics , psychology , social psychology , linguistics , philosophy , quantum mechanics
The process of physical aging is accompanied by a gradual change in a number of physical parameters of the solid under study. In this paper we show that by correlating the excess enthalpy with the excess volume, bulk modulus, K , data of reasonable magnitude are obtained for polystyrene, PS, and poly(vinyl acetate), PVAc. The underlying reasoning is based on standard equilibrium thermodynamics. For PVAc the time dependence of K during the aging process is discussed in terms of corresponding data calculated from dynamic mechanical measurements at varying frequency. Examples are also given of calculations of K from uniaxial stress relaxation data obtained with polyethylene samples where both the volume and the con comitant stress changes were determined. The calculation of K was based on the usual formula relating pressure (1/3rd of the uniaxial stress) to the corresponding volume change. The K data obtained were somewhat lower than those normally reported, an effect likely to be related to the time scale involved.