Abstract
The interplay of screw speed and residence time during polymer blend extrusion profoundly influences blend properties. Herein, blends of styrene-ethylene-butylene-styrene (SEBS) and polystyrene (PS) containing 30% by weight PS were prepared at a constant feed rate but different screw speeds (50, 100, 200 and 300 min−1). The blend produced at 100 min−1 (B100) possessed a finer morphology, better mechanical and rheological properties, attributed to suitability of residence time and viscosity ratio. When batch foamed with carbon dioxide at 110°C and 100°C, all blends produced stable foams. B100 foams exhibited higher volume expansion ratio (VE) due to higher complex viscosity and storage modulus. When foaming was conducted at 35°C, all foams shrank. B100 foams possessed higher cell density, lower VE and showed faster shrinkage due to increased nucleation and hindered expansion by the finely dispersed stiff PS aggregates during selective foaming of the elastomeric phase.
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