Research on improved gas‐assisted extrusion of plastic sheets based on time–temperature equivalence principle

Abstract Based on the time–temperature equivalence principle, the relationship between the melt relaxation time (MRT) and melt heating temperature (MHT) in an improved gas‐assisted extrusion (GAE) of a polypropylene (PP) sheet was investigated by numerical simulations. In the simulations, the MRT was varied and the inherent properties of the MHT were controlled using experimental methods. With an increase in MRT, the velocity in all directions, pressure drop, and shear rate of the melt increased; however, increasing the MRT does not always yield a positive effect on the GAE process of the melt. For instance, the melt velocity increased vertically at the die exit with MRT, resulting in an outward extrudate swell. In addition, the extruded product was intact when the melt was heated to 220°C, which verified the principle of time–temperature equivalence.