A SIMPLE-MODEL TO PREDICT EXTRUDATE SWELL OF POLYSTYRENE AND LINEAR POLYETHYLENES

In a previous paper (Guillet and Seriai, 1991) we derived a simple ana lytical expression which allows the prediction of extrudate swell of p olystyrene in a wide range of residence time. This was done using the rubberlike elasticity theory and calculation of the elongational strai n recovery of a Lodge fluid. The theoretical extrudate swell ratio mai nly depends on the relaxation modulus, the extension ratio and the rec overable shear strain. The main advantage of this model is to provide good accuracy with short dies in a wide range of shear rate. In this p aper, we examine the validity of the proposed equation with different contraction ratios at the die entrance (ECR) and its ability to predic t extrudate swell of other commodity polymers such as polyethylenes.