Effect of the Convergent-Filamentary Die Geometry on Volume Expansion of PS Foams Blown with CO ₂

This paper presents the effects of the convergent-filamentary die geometry on the volume expansion behaviors of extruded PS foams blown with supercritical CO ₂ . Three groups of interchangeable convergent-filamentary dies were designed to thoroughly represent the die parameters. The experimental results reveal that the die geometry affects volume expansion of the extruded foams through its influences on the die pressure, the pressure-drop rate, and the amount of premature cell growth inside a convergent-filamentary die. Compared with the constant pressure-drop rate for a straight die, the pressure-drop rate for a convergent die increases along the die land, which is favorable for promoting cell nucleation and suppressing premature cell growth. Although the convergent shape is favorable for volume expansion, foams with a low expansion ratio were produced for those dies with a low pressure and a low pressure-drop rate because of the promoted premature cell growth.