| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 102 === In this study, the crystallization and thermal degradation behaviors of poly(ethylene naphthalate) (PEN) were investigated using different instruments. This study contains three parts. In the first part, isothermal crystallization experiments were performed from 190 to 250°C by differential scanning calorimeter (DSC). The crystallization kinetics was analyzed via Avrami equation. The micrographs obtained from polarized light microscope (PLM) showed that α-form crystals were banded spherulites with negative birefringence and β-form crystals were fribril spherulites with positive birefringence. The maximum growth rate was 1.29×10-2 μm/sec at 210°C. Wide angle X-ray diffraction (WAXD) patterns display -form when crystallized below 226°C and β-form formed above 227°C. The melting behavior after isothermal crystallization was investigated by DSC. -form crystals presented melting-recrystallization-remelting behavior and β-form crystals showed dual morphology. Equilibrium melting temperatures were obtained by Hoffman-Weeks linear plots: -form gave 286.2°C, and β-form yielded 295.5°C. The second part focused on the non-isothermal crystallization of PEN. DSC was conducted at a cooling rate of 0.1, 0.5, 1, 3, or 5°C/min. Nonisothermal crystallization kinetics of α- and β-form crystals were analyzed and compared using modified Avrami, Ozawa, and Mo equations. PLM was performed at a cooling rate of 3°C/min that lasted 40 min. Continuously isothermal growth rates of crystals were obtained with a non-bell shape. This non-bell curve was deconvoluted into two curves that correspond to the growth rates of α- and β-form crystals, separately. Regime analysis was then applied to these two curves. TII→III was found around 228°C for α-form crystals and 246°C for β-form crystals. Kissinger equation was used to evaluate the effective activation energy. The value was 127.8 kJ/mol for -form crystal and 220.9 kJ/mol for β-form crystal.
The third part was to study the thermal stability of PEN under nitrogen at heating rates of 1, 3, 5, and 10°C/min via thermogravimetric analyzer (TGA). The model-free methods of Friedman and Ozawa equations were adopted to evaluate the activation energy of thermal degradation in each period of mass loss. The average activation energy, 194 kJ/mol, was then used to fit the mass loss using the nth-order and autocatalysis nth-order model-fitting mechanisms. Additionally, TGA-FTIR under nitrogen was used to monitor the thermal degradation products of PEN at 5ºC/min. FTIR spectra revealed that the major gas products had CO2 and aldehydes, and β- hydrogen scission occurred before α-hydrogen bond scission. Thermal degradation products may contain ethanedial, 2-naphthaldehyde, ethenone, 2,6-naphthalene dicarboxaldehyde and 2,6-naphthalene dicarboxylic acid.
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