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]