Phase behavior and morphology of SAN/PMMA under high flow rates

The effect of shear flow on phase behavior of styrene acrylonitrile copolymer (SAN)/poly(methyl methacrylate) (PMMA) blend at industrially realistic shear rate was investigated. The effect of shear flow on miscibility of SAN/PMMA was also investigated indirectly through the morphology of injection-molded specimens by using optical and transmission electron microscopy.; The shear-induced phase separation of SAN/PMMA was observed on-line at moderate shear rate and viscous shear heating was found to be the cause of phase separation at very high shear rate. Viscous shear heating was also the cause of phase separation in the injection-molded SAN/PMMA specimens processed at one-phase temperature. Two-phase opaque layered structures were found in the gate section of injection-molded specimens. Transparent skin and alternating translucent opaque concentric elliptical layers were found in specimens processed at two-phase temperatures. The structures in the specimens processed by ram injection molding are symmetrical while those processed by conventional injection molding are asymmetric. Asymmetrical morphology between left and right of the conventional injection-molded samples is caused by asymmetric flow history complicated by a number of abrupt turns that the flowing polymer melt undergoes while passing through junctions and curves in the runner system. The major variables affecting these structures are injection speed and barrel temperature. The result shows that the formations of these structures are controlled by the competition between mechanisms of viscous shear heating and shear-induced mixing.; The concentration fluctuations from skin to core of the injection-molded specimens were investigated by micro-Raman spectroscopy technique. This shows that the processing conditions have only slight effect on the composition uniformity of this blend.