Modulated differential scanning calorimetry in the glass transition region. V. Activation energies and relaxation times of poly(ethylene terephthalate)s
✍ Scribed by Iwao Okazaki; Bernhard Wunderlich
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 972 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
Temperature-modulated differential scanning calorimetry is used to evaluate the kinetics of the glass transition from measurement of the first harmonic of the apparent, reversing heat capacity. The data are taken from quasi-isothermal experiments with negligible instrument lag, extrapolated to zero modulation amplitude. Equations based on irreversible thermodynamics that can be understood in terms of the hole theory of liquids are applied to measurements on amorphous, semicrystalline, and biaxially drawn poly(ethy1ene tere-phtha1ate)s (PET). The activation energy of amorphous PET decreases from 328 to 153 kJ/mol on crystallization and to 111 kJ/mol on orientation, and is correlated with an increase in the preexponential factor. After annealing of the crystallized samples below the glass transition temperature, the activation energy of the semicrystalline PET can recover beyond the level of amorphous PET, to 387 kJ/mol. The earlier observed decrease in enthalpy relaxation on crystallization is linked to this sharp decrease in activation energy. 0