DETERMINATION OF PARTITION-COEFFICIENTS AND RESIDUAL SOLVENT FOR POLYMER DRYING APPLICATIONS

Gas-solid partition coefficients (K) for n-hexane in high density poly ethylene (HDPE) have been measured at conditions applicable to large-s cale drying utilizing a novel headspace method. The method features co nsiderable versatility and simplicity due to the control of experiment al conditions designed to favor full extraction of the analyte into th e headspace. By combining this full extraction technique with a tradit ional static headspace experimental scheme, a method which measures K and residual concentration is achieved. The results show that partitio n coefficients differ significantly between HDPE in its virgin powder and pellet forms, as well as among various HDPE grades. The difference s are shown to be attributable to differences in % crystallinity of th e specific polymer. Data collected over a wide range of hexane concent rations reveals saturation levels (solubilities) which correspond to c rossover from evaporative to diffusion-controlled drying.