A simple model to predict extrudate swell of polystyrene and linear polyethylenes

In a previous paper (Guillet and Seriai, 1991) we derived a simple analytical expression which allows the prediction of extrudate swell of polystyrene in a wide range of residence time. This was done using the rubber-like elasticity theory and calculation of the elongational strain recovery of a Lodge fluid. The theoretical extrudate swell ratio mainly depends on the relaxation modulus, the extension ratio and the recoverable 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 paper, we examine the validity of the proposed equation with different contraction ratios at the die entrance (ECR) and its ability to predict extrudate swell of other commodity polymers such as polyethylenes.