A Study on Physical Aging of Semicrystalline Polyethylene Terephthalate below the Glass Transition Point

 

M. Farhoodi¹, S. M. Mousavi², R. Sotudeh-Gharebagh³, Z. Emam-Djomeh*⁴, A. Oromiehie⁵, H. Mansour⁶

 

^{1 2, 4} Department of Food Science and Technology, Faculty of Agricultural Engineering, University of Tehran, P.O. Box 31587-77871, Karaj, Iran, *emamj@ut.ac.ir.

³ School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11155/4563, Tehran, Iran.

⁵ Iran Polymer and Petrochemical Institute, P.O. Box: 14965/159, Tehran, Iran.

⁶ Iranian Offshore Oil Company, P. O. Box 79781-79717, Lavan, Iran.

 

Abstract

Physical aging of semicrystalline polyethylene terephthalate was studied using differential scanning calorimetry (DSC). PET samples with crystallinity content of 0.28 were aged at two different temperatures, 25 and 45°C. The samples were stored for several days and periodically tested using DSC method. The glass transition temperature for the samples aged at 25°C was about 73-74°C, and the position and intensity of endothermic peaks were approximately constant. Higher glass transition of the samples aged at 45°C, 73-86°C, was attributed to the enthalpy relaxation process of amorphous regions of semicrystalline PET. For the samples aged at 45°C, the endothermic peaks shifted to higher temperatures with increasing aging time. The position of the endothermic peaks determined by the temperature of the maximum, Tmax, tended to increase with aging time for samples aged at 45°C, and the intensity of the peaks continuously increased with time; however, the results showed that the aging of PET samples at 45°C even after 120 days continued the enthalpic relaxation of semicrystalline PET and that the process could be studied by DSC method. The results also showed that the aging process could affect the final degree of crystallinity of c-PET samples and the samples stored at 45°C showed higher degree of crystallinity than the samples aged at 25°C.

Keywords: Enthalpy Relaxation, Glass Transition, Endothermic Peak, Polyethylene Terephthalate, Crystallization.

 

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References

[1] Wunderlich B., Macromolecular Physics, Academic Press, New York, 1976, Vol. 2, Ch.7.         [ Links ]

[2] Struik L. C. E., Physical aging in amorphous polymers and other materials, Elsevier Amsterdam, 1978.         [ Links ]

[3] Struik, L. C. E., The mechanical behaviour and physical ageing of semicrystalline polymers: 2, Polymer, Vol. 28, No. 9, 1987, pp.1534-1542.         [ Links ]

[4] Lu X. & Hay J. N., The effect of physical aging on the rates of cold crystallization of poly(ethylene terephthalate), Polymer, Vol. 41, No. 20, 2000, pp. 7427-7436.         [ Links ]

[5] Ellis A., Gordon D., King S. & Jenkins, M., Physical ageing studies of poly(ethylene terephthalate) using SANS and DSC, Physica B: Condensed Matter, Vol. 385-386, No. I, 2006, pp. 514-516.         [ Links ]

[6] Doulache N., Khemici M. W., Gourari A. & Bendaoud, M., DSC study of polyethylene terephtalate's physical ageing, Proceedings of the 2010 IEEE International Conference on Solid Dielectrics (ICSD 2010), art. no. 5568072.         [ Links ]

[7] Deng M., Allan J. M., Corbett J. T. & Shalaby S. W., Effects of Thermal History and Physical Aging on Thermal Properties of Poly-L-Lactide, ASTM Special Technical Publication, Vol. 1396, 2000, pp. 58-68.         [ Links ]

[8] Zhou H., Lofgren E. A. & Jabarin, S. A. Effects of microcrystallinity and morphology on physical aging of poly (ethylene terephthalate), Journal of Applied Polymer Science, Vol. 106, No. 5, 2007, pp. 3435-3443.         [ Links ]

[9] Zhou H., Lofgren E. A. & Jabarin S. A., Effects of microcrystallinity and morphology on physical aging and its associated effects on tensile mechanical and environmental stress cracking properties of poly (ethylene terephthalate), Journal of Applied Polymer Science, Vol. 112, No. 5, 2009, pp. 2906-2917.         [ Links ]

[10] Starkweather H. W., Zoller P. & Jones G. A., Heat of Fusion of Poly(ethylene terephthalate), Journal of polymer science. Part A-2, Polymer physics, Vol. 21, No. 2, 1983, pp. 295-299.         [ Links ]

[11] Illers K. H. & Breuer, H., Molecular motions in polyethylene terephthalate, Journal of Colloid Science, Vol. 18, No. 1, 1963, pp. 1-31.         [ Links ]

[12] Montserrat S. & Cortes P., Physical ageing studies in semicrystalline poly (ethylene terephthalate), Journal of materials science, Vol. 30, No. 7, 1995, pp. 1790-1793 [         [ Links ]13] Atkinson J., Hay J. & Jenkins M., Enthalpic relaxation in semi-crystalline PEEK, Polymer, Vol. 43, No. 3, 2002, pp. 731-735.         [ Links ]

[14] Karagiannidis P. G., Stergiou A. C. & Karayannidis G. P., Study of crystallinity and thermomechanical analysis of annealed poly (ethylene terephthalate) films, European Polymer Journal, Vol. 44, No. 5, 2008, pp. 1475-1486.         [ Links ]