The crystallization kinetics and the melting behavior of a random copolyester with equal amounts of ethylene- and trimethylene- terephthalate units were studied by using a modulated differential scanning calorimeter in both conventional mode (DSC) and modulated mode (TMDSC). Polarizing light microscope (PLM) was used to study the spherulite growth rates and spherulite patterns. Isothermal crystallization was performed at temperatures (TC) between 115 and 142¢J. The Avrami exponents, n1, were found to increase from 3.00 to 3.22 with an increasing TC. At the highest TC, it should be a sporadic nucleation with spherical growth, i.e. n1 = 4. The value of n1 less than 4 and the slow rate of crystallization indicate that both primary and secondary crystallization occurs in parallel rather than in series. Triple- and double- melting peaks were observed for the melting behavior of DSC at 10¢J/min and of TMDSC at 2¢J/min. The results of WAXD, DSC and TMDSC indicate the coexistence of two melting mechanisms, i.e., dual morphologies and the recrystallization process. The Hoffman-Weeks plot gave an equilibrium melting temperature of 176.6¢J from the reversing curves of TMDSC. In this study, the regime II¡÷III transition temperature can be estimated from the inverse of the half-time of crystallization as overall growth rate and the growth rate. Meanwhile, a clear change in morphology from negative regular to banded spherulites was also observed around 132¢J by using PLM.
The heat of fusion of polymer is customarily evaluated through the melting point depression measurements with the thermodynamic melting points. Application of the Flory equation to the PET/PTT random copolyesters diluted with di-n-butyl phthalate gave the values of the heat of fusion to be 4.48, 3.43 and 3.07 kcal/mole, respectively, for the random copolyesters containing 28, 38 and 50 mole % of ethylene terephthalate unit. The corresponded values of the interaction energy of mixing at infinite dilution were 3.90, 2.85 and 2.75 cal/cc.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0713104-205543 |
| Date | 13 July 2004 |
| Creators | Chang, Chih-wei |
| Contributors | E. M., Woo, Ming Chen, An-chung Su, Guo-ping Chang-Chien |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0713104-205543 |
| Rights | withheld, Copyright information available at source archive |
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