RATE AND EXTENT OF SUPERCRITICAL-FLUID EXTRACTION OF ADDITIVES FROM POLYPROPYLENE - DIFFUSION, SOLUBILITY, AND MATRIX EFFECTS

Analytical extraction of additives from polymers using a supercritical fluid (SFE) is a promising alternative to liquid extraction. Factors affecting SFE with carbon dioxide of Irpfos 168 and Irganox 1010 from commercial polypropylene have been studied, with analysis of extracts by capillary supercritical fluid chromatography (SFC). A diffusion lim ited extraction model was investigated by measuring the rate of SFE as a function of pressure, particle size, flow rate, and temperature. Th e rate of extraction was found to fit the sum of exponential decays; r esults were also consistent with an extrapolation procedure to obtain the total mass of additive without exhaustive extraction. Derived diff usion coefficients for the additive in polypropylene differed from lit erature values by approximately two orders of magnitude apparently bec ause of swelling of the polymer by sorbed carbon dioxide. The variatio n of extraction rate with pressure and flow rate confirmed the solubil ity limitation of proposed model. The rate of extraction increased bet ween 20 and 140-degrees-C, then fell away at higher temperatures with the onset of melting.