STUDY OF THERMOPLASTIC FOAM SHEET FORMATION

This paper discusses theory and experiments on nonisothermal foam grow th during foam sheet formation in an extrusion process. The extruded f oam sheet expands and cools simultaneously when exposed to ambient tem perature. A viscoelastic cell model in the Literature was modified to include heat transfer and gas loss effects during foam sheet formation . Experiments were conducted using a twin-screw extruder to study the effect of ambient temperature and initial sheet thickness on foam char acteristics. The foam was made using low-density polyethylene with CFC -12 as the blowing agent. The experimental results are compared with t heoretical predictions to check the validity of the model. The results reveal that heat transfer effects become important when sheet thickne ss decreases to the millimeter range. Agreement between theory and exp eriment is good when an appropriate boundary condition, to account for the gas loss, is included in the model.