Parameters affecting the in-line measurement of gas solubility in thermoplastic melts during foam extrusion

Abstract

The knowledge of gas solubility at processing conditions is of paramount importance for the understanding and optimization of extrusion foaming by gas injection. A recently developed in-line optical method is used to generate data of the solubility of atmospheric gases in PS and PET in single or twin screw extruders with gas injection capabilities. Overall, the in-line data compare favorably with off-line data where Henry's law constants were obtained from the slope of solubility/equilibrium gas pressure plots. Results obtained with the twin-screw extruder configured for improved mixing indicate a) better data consistency, presumably as a result of enhanced homogenization/dissolution and longer residence time and, b) a higher degree of sensitivity in detecting differences in the solubility of different gases.