Crystallizations of poly(ethylene terephthalate co ethylene isophthalate)

Crystallization behaviors of crystallizable poly(ethylene terephthalate co ethylene isophthalate) with different molar ratios of polyethylene terephth alate (PET) to polyethylene isophthalate: (PEI) were studied both non-isoth ermally and isothermally by differential scanning calorimetry (DSC). Avrami and Ozawa plots were used to describe the non-isothermal crystallizations. However, the Avrami treatment cannot predict the mechanisms of non-isother mal crystallizations for the above copolyesters, while the Ozawa explanatio n can be taken to reveal that the non-isothermal crystallization is dominat ed by heterogeneous nucleation. The activation energies of crystallization were calculated from the Kissinger equation. The copolyester 90/10 shows sy nergistic effects on non-isothermal crystallization, in that it has the low est activation energy of crystallization. Isothermal crystallizations were explained by Avrami plots. From lower degrees of supercooling to higher one s, the crystals of the copolyesters grow from low dimension to multidimensi ons, but the crystallization rates become lower. The percentage of spheruli te growth of the copolyester 100/0 (PET homopolymer) is higher than that of the other copolyesters under the same degree of supercooling. Equilibrium crystallization temperatures (T-c(0)) and melting temperatures (T-m(0)) wer e postulated respectively. T-c(0) and T-m(0) decrease with the increasing c omposition of PEI, indicating that the equilibrium crystals of the copolyes ters become imperfect. With involvement of PEI, the copolyester is not like ly crystallizable perfectly and the crystal becomes less perfect. (C) 1999 Elsevier Science Ltd. All rights reserved.