Heat capacity of poly(trimethylene terephthalate)

Abstract

The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol−1. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol−1. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ1 = 550.5 K and θ2 = θ3 = 51 K, Nskeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: \documentclass{article}\pagestyle{empty}\begin{document}$ C^L_p(exp) $\end{document} = 211.6 + 0.434 T J K−1 mol−1 and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310–315 K with a ΔCp of about 94 J K−1 mol−1. Knowing Cp of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid‐amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499–2511, 1998

Structural variation of melt-crystallized PTT during the heating process revealed by FTIR and SAXS

“…However, for the PTT sample prepared by cooling from melt to room temperature at a rate of 10°C/min, there is little evidence to support the mechanism of melting of crystalline entities with different stability. An ordered exothermal peak between the minor endothermic peak and the major melting peak has been revealed by Pyda et al [10] during the heating process of PTT with high crystallinity. This report seems to support the melting-recrystallization-remelting mechanism.…”

“…In addition, in the enlarged insert of Figure 1(b), an endothermic phenomenon between dash lines is observed just prior to the exothermal peak. Pyda et al [10] explained it by the melting of small and defective crystallites base on their MDSC results. To further disclose the structural changes between glass transition and ultimate melting temperature, the heating process of PTT sample obtained by cooling its melt to room temperature at 10°C/min is studied in detail here via IR technique.…”

“…These disordered and restricted molecules will overcome the restriction and improve the structure if the relatively lower thermal energy is supplied. This explanation differs from the proposal of the pre-melting of imperfect crystals by Pyda et al [10], which may origin from the employed different techniques and molecular weight of PTT. With further increase of temperature, the intensities of all bands in Figure 3(a) and (b) change abruptly.…”

“…The three phase structure of PTT is described as crystalline lamella, mobile amorphous phase (MAP) between lamellae and rigid amorphous phases (RAP) associated with the crystalline-amorphous interface [20][21][22][23][24]. The MDSC results of Pyda et al [10] suggest, however, that there is no or little rigid amorphous PTT when it is cooled down from the melt to room temperature at a rate of 10°C/min. In order to investigate the structural development and the corresponding thermal behavior of PTT cooled from the melt to room temperature at a rate of 10°C/min, techniques includes Fourier transform infrared spectroscopy (FTIR) and X-ray scattering and diffraction were employed in the present work.…”

Preparation and characterization of nanocomposites based on COOH functionalized multi-walled carbon nanotubes and on poly(trimethylene terephthalate)

“…the weight fraction crystallinity) was determined according to Equation (2) as the ratio of the integrated heat of fusion "H m value of the sample over the heat of fusion of fully crystalline PTT, i.e. "H m 0 = 145.6 J/g [3,33]:…”