Isothermal crystallization behavior of poly(trimethylene terephthalate) at high undercoolings

Abstract

After successfully being commercialized in the 1990s, poly(trimethylene terephthalate) (PTT) has drawn more and more attention due to its superior characteristics, such as elastic recovery, chemical resistance and resilience in comparison with poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT) [1, 2]. PTT is a typical semicrystalline polymer material and many reports were focused on its crystallization behaviors recently. Huang and Chang [3] investigated the crystallization behavior for PTT from the melt and analyzed the kinetics in the temperature range from 451 K to 483 K, some important parameters for crystallization such as equilibrium melting temperature(Tm 0 = 521 K), lateral surface-free energy (r),work of chain folding (q) were also reported. Crystallization kinetics parameters of PET, PTT and PBT were compared by Chuah [4], it could be concluded that PTT crystallized faster than PET but slower than PBT at the same degree of undercooling. Hong and his coworkers [5] took note of the inaccuracy of Chang and Huang in determining the work of chain folding (q) and gave a more reasonable value of 27.2 kJ mol, they also investigated the regime behaviors of PTT crystallization using the secondary crystallization theory [6] and found the boundaries between the classical regime I fi II and regime II fi III are located at 488 and 468 K, respectively. We also carried out the kinetics analysis of PTT crystallization including the secondary crystallization process using a new mathematical model constructed by us [7]. Much of the above work has concentrated on the measurement of overall rate of crystallization or the measurement of spherulitic growth rate of PTT crystallization from melt at low and moderate degrees of undercooling (DT = Tm –Tc, Tc is crystallization temperature), yet a detailed overall kinetics analysis at high undercoolings (DT > 70 K), especially in the temperature range where the fastest crystallization rate would occur is still lacking. However, study of the behavior of a semicrystalline polymer crystallizing in this temperature range is of great importance from both theoretical and practical view points. Of theoretical importance is the mechanism of nucleation, the growth geometry of crystals and the formation of polymer fine structure during crystallization. The practical importance is that such crystallization data may be very useful to polymer processing such as fiber spinning and injection molding, because most polymer shaping processes need a very fast crystallization rate to shorten the solidifying time. The importance also arises from the effect of final crystallinity on the physical and chemical properties of polymers. In this study, we present the isothermal crystallization behavior of PTT from 356 K to 465 K, the overall crystallization kinetics data in the temperature range 356–450 K was reported for the first time. Poly(trimethylene terephthalate) samples with different molecular weights were obtained by the polycondensation of terephthalic acid in the melt phase with 1,3-propandediol using different reaction time Y. Xu (&) H.-b. Jia Department of Polymer Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China e-mail: njust_xuy@hotmail.com