Morphological and Conformational Changes of Poly(trimethylene terephthalate) during Isothermal Melt Crystallization

Abstract

The isothermal melt crystallization of poly(trimethylene terephthalate) (PTT) has been investigated using differential scanning calorimetry (DSC), optical microscopy, and Fourier transform infrared (FTIR) spectroscopy. Triple-melting endotherms were dominant at crystallization temperatures (T(c)) below 195 °C, while double-melting endotherms were dominant at T(c) above 195 °C. These multiple-melting behaviors were attributed to melting and recrystallization as well as thermal stability of the crystallites. The difference in crystallinity observed between melt-crystallized PTT films before and after cooling to room temperature was attributed to lamellar thickening. The kinetics of isothermal melt crystallization of PTT was analyzed using an Avrami equation, and the rate constant (k) and t(1/2) increased with increasing T(c). An Avrami exponent n = 2-3 was obtained for the PTT melt crystallized from 150 to 205 °C, suggesting two-dimensional to three-dimensional growth with heterogeneous nucleation and was confirmed by polarized optical microscopy. The bands at 1358 and 976 cm(-1) associated with gauche and trans conformations of -OCH(2)CH(2)CH(2)O- were used to determine gauche and trans conformations assuming a two-phase conformational model. The crystalline and the amorphous gauche conformations were separated by combining them with DSC crystallinity. It was shown that the crystalline gauche conformation increased at the expense of the amorphous trans conformation. No significant change in the amorphous gauche conformation was found. On the other hand, the crystalline and amorphous gauche conformations were found to increase with the annealing temperature (T(a)) at the expense of the trans conformations during the annealing of PTT. The difference between melt crystallization and annealing was also discussed.

Effect of clay on melt crystallization, crystallization kinetics and spherulitic morphology of poly(trimethylene terephthalate) nanocomposites

“…The T m shows no significant change with either melt crystallization temperature or clay content. The T m observed for the melt crystallized neat PTT and PTT nanocomposites shows multiple peaks and similar observation was previously made for melt crystallized neat PTT [46]. Multiple melting peaks in the DSC scans was interpreted by either the melting of the recrystallized original crystals of the PTT and PTT nanocomposites or due to the varying lamellar thickness.…”

“…The optical micrographs observed for PTT nanocomposites show relatively well defined spherulitic morphologies with clear maltese cross patterns. It has been previously shown that spherulite size increases with increasing melt crystallization temperatures of neat PTT films [46]. It appears that increasing the melt crystallization temperature of neat PTT from 110 • C (Fig.…”

Crystallization Studies of Poly(trimethylene terephthalate)/Silica Nanocomposites Prepared by Sol–Gel Technique

“…44 The banded spherulites were dominant at crystallization temperature above 195 °C (regime II) and the banded morphology disappears at crystallization temperature below 195 °C, in good agreement with our previous observation. 5 In the present study, banded spherulites were seen for PTT nanocomposites with small amount of SiO 2 at 120 °C. Bands in these spherulites appear to be in regular interval with dark and bright bands.…”

“…Effect of melt crystallization temperature on spherulitic morphology of PTT was studied previously. 5,43,44 It was apparent that spherulite size increased with increasing crystallization temperature for both neat PTT and PTT nanocomposites. Figure 4 displays PTT with 5 wt % TEOS melt crystallized at 120, 150, and 180 °C for 30 min.…”

“…PTT has better elastic recovery and low modulus than PET, PBT, and polyamide 6, and it is an ideal candidate for soft and stretchable fibers. 1−5 PTT was first synthesized in 1941 using propane diol and dimethyl terephthalate. It was not commercially available until 1998 due to the cost of propane diol.…”