DYNAMIC SOLUBILITY OF CARBON DIOXIDE IN POLYPROPYLENE MELT

摘要

A testing method has been developed to measure the dynamic solubility of polymer/gas mixtures at high pressures and a wide range of melt temperatures. This method utilizes tandem extruders equipped with a high- pressure optical slit cell; a camera; a set of pressure transducers; and a metering valve for back-pressure control. This in-line visualization system provides a direct way to investigate the dynamic solubility within a wide range of processing conditions (i.e, melt pressure, melt temperature, gas content, and flow rate). The measurements were carried out for various amounts of CO2 dissolved into branched polypropylene (PP) melt at two different temperatures. The dynamic solubility was estimated based on the degassing pressure when the second phase starts to nucleate. The experimental results showed that the dynamic solubility of carbon dioxide in PP melt increased with system pressure but decreased with melt temperature. It was also found that a higher flow rate, which corresponds to a higher shear rate, decreased the dynamic solubility of CO2 in branched PP.