Rate and extent of supercritical fluid extraction of additives from polypropylene: Diffusion, solubility, and matrix effects

Abstract

AbstractAnalytical extraction of additives from polymers using a supercritical fluid (SFE) is a promising alternative to liquid extraction. Factors affecting SFE with carbon dioxide of Irgafos 168 and Irganox 1010 from commercial polypropylene have been studied, with analysis of extracts by capillary supercritical fluid chromatography (SFC). A diffusion limited extraction model was investigated by measuring the rate of SFE as a function of pressure, particle size, flow rate, and temperature. The rate of extraction was found to fit the sum of exponential decays; results were also consistent with an extrapolation procedure to obtain the total mass of additive without exhaustive extraction. Derived diffusion coefficients for the additive in polypropylene differed from literature values by approximately two orders of magnitude apparently because of swelling of the polymer by sorbed carbon dioxide. The variation of extraction rate with pressure and flow rate confirmed the solubility limitation of proposed model. The rate of extraction increased between 20 and 140°C, then fell away at higher temperatures with the onset of melting. © 1993 John Wiley & Sons, Inc.