Effect of aging time on a glass transition of amorphous polymers at heating
aUniversity Institute, Tomas Bata University in Zlin, Nad Ovcirnou 3685, 760 01 Zlín, bInstitute of Hydrodynamics, Academy of Sciences of the Czech Republic, 166 12 Prague, cCentre of Polymer Systems, University Institute, Tomas Bata University in Zlin, Nad Ovcirnou 3685, 760 01 Zlín, Czech Republic, dChalmers University of Technology, Polymeric Materials and Composites, 412 96 Gothenburg, Sweden, ePolymer Centre, Faculty of Technology, Tomas Bata University in Zlin, nám. T.G. Masaryka 275, 762 72 Zlín, Czech Republic
The relaxation and consolidation processes accompanying the glass transition are linked in this paper with an induction mechanism introducing a cooperative character of relaxation into those processes. The induction mechanism supplements the proposition underlying the internal energy material clock used in a recently developed thermodynamically consistent non-linear viscoelastic theory modeling thermal and mechanical behavior of amorphous polymers in the glass transition range1,2. The mechanism is introduced into the constitutive theory framework where it replaces the stretched exponential relaxation functions. The proposed modification is used to describe the dilatometric behavior of PMMA during heating from the glassy state after varying aging times.
The modified theoretical approach is found to produce a fairly good description of the peaks in thermal expansivity, both with regard to their intensity and position along the temperature axis. The length of the aging period in the glassy state is found to affect the material time scale while the relaxation functions are unchanged.
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