Creep and Stress Relaxation in a Longitudinal Polymer Liquid Crystal:
Prediction of the Temperature Shift Factor
Witold Brostow, Nandika Anne D'Souza, Josef Kubat,
and Robert Maksimov
Departments of Materials Science and Chemistry
University of North Texas
Denton, TX 76203-5310, USA
ABSTRACT
The polymer liquid crystal PLC is the PET/0.6PHB copolymer; PET=poly(ethylene
terephthalate), PHB=hydroxybenzoic acid (LC): 0.6=the mole fraction
of PHB. This is a multiphase system with PHB-rich islands in the
PET-rich matrix. Tensile creep compliance was measured isothermally
from 20 C to 160 C in 10 C intervals. Master curves were determined
using the time-termperature superposition for 20 C and for the glass transition
temperature of the PET-rich phase TgPET=62 C. Experimental values
of the temperature shift factor aT as a function of temperature T agree
in the entire T range with those from Eq. (7) relating aT to the reduced
volume and the Hartmann equation of state Eq. (10). Values of aT(T) calculated
from the Williams-Landel-Ferry (WLF) formula give very large errors below
Tg. A control 14 months creep experiment agrees with the theoretical
predicitions from Eq. (7). Stress relaxation experiments were prerformed
under the constant strain of 0.5% from 20 C to 120 C, again master curves
were determined for 20 C and for TgPET and aT(T) values calculated.
The stress relaxation aT(T) results agree with those from creep and with
those from Eq. (7). Copyright 1999 American Institute of Physics.
[S0021.9606(99)51218-X]
Maintained by Manus Donahue
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