In-Line NIR Monitoring of Composition and Bubble Formation in Polystyrene/Blowing Agent Mixtures

Abstract

The composition of mixtures of polystyrene (PS) and blowing agent (HCFC 142b) was monitored by means of near infrared (NIR) transmission probes located in the die at the end of an intermeshing co-rotating twin-screw extruder. The PS resin was extruded while the HCFC was injected at high pressure and various concentrations. Using chemometrics techniques like PLS to model the differences in the NIR spectra, the composition of PS/HCFC mixtures could be predicted accurately with a standard error of prediction (SEP) below 0.2 wt%. Accurate composition prediction was still possible in the presence of a small amount (<5% wt) of nucleating agent like talc. In-line NIR spectroscopy was also an effective technique to detect bubble formation in the die as a function of HCFC concentration and pressure.