Crystallization of poly(ethylene terephthalate) induced by carbon dioxide sorption at elevated pressures

✍ Scribed by S.M. Lambert; M.E. Paulaitis

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 896 KB
• Volume: 4
• Category: Article
• ISSN: 0896-8446
• DOI: 10.1016/0896-8446(91)90026-3

✦ Synopsis

Experimental results are reported for the crystallization and sorption kinetics of poly(ethylene terephthalate) in the presence of CO2 at 35 "C and pressures of 40,50, and 60 atm. The results show that the time scale for crystallization is significantly greater than the time scale for CO2 sorption at these conditions. Crystallization occurs uniformly throughout the polymer film in this kinetic regime, and the sorption isotherm is characterized by a maximum in CO2 solubility as a function of time.

The effect of increasing CO2 pressure over the pressure range studied is to enhance both the sorption and crystallization kinetics, although larger rate enhancements are obtained for crystallization. These results suggest that crystallization may occur on a time scale less than that for sorption at even higher CO2 pressures. Crystallization would not occur uniformly throughout the polymer in this kinetic regime, but would move as a front through the polymer film. The morphology of thin polymer films which undergo crystallization at higher pressure may therefore be substantially different from the morphology obtained by crystallization at the CO2 pressures studied here.

This work has general significance for dense gas or supercritical fluid extractions of low molecular weight components from polymeric materials. Our results show that the effect of pressure on the extraction can involve more than the solvent properties of the dense gas or supercritical fluid; the effect of pressure on the relative rates of crystallization and sorption, and on polymer morphology must also be considered. The results of this study also suggest that CO2 pressure may be used to control the kinetics of crystallization and sorption in thin films of poly(ethylene terephthalate) and thereby provides the means to manipulate the morphology of this semi-crystalline polymer.