Diffusion of ethylene glycol in melt and solid state poly(ethylene terephthalate)

Abstract

Diffusivity of EG in melt and solid state PET was obtained by using the quartz spring sorption apparatus. The quartz spring has a maximum extension of 500mm and its corresponding maximum weight of 1 gram. The change of spring length was measured by Cathetometer with the accuracy of $10^{-4}$cm. The temperature of sorption apparatus was controlled by the silicon oil jacket. Diffusivity of EG was determined by fitting iteratively the experimental data of sorption and desorption with the modeling developed to consider both diffusion and reactions simultaneously. The diffusion coefficient of EG(Deg) in solid state PET is found to be proportional to the volume fraction of amorphous region of PET sample, and Deg is $2.75\times 10^8cm^2/sec$ at 230℃, $X_c$ = 0.373. The activation energy for diffusion in solid state PET is 51.8 kcal/gmol, which is slightly higher than that of melt state. In PET melt, diffusion coefficient of EG in the limit of zero-concentration is found to be $4.47\times 10^{-7}cm^2/sec$, and the activation energy for diffusion is 39.5 kcal/gmol. It is found that the diffusivity of EG for desorption is slightly larger than one for absorption, which results from the concentration effect of diffusivity. The heat of solution for sorption in PET melt is 54.7 kcal/gmol.