SUPERCRITICAL CARBON DIOXIDE ASSISTED POLYMER BLENDING IN TWIN-SCREW EXTRUSION: PHASE INVERSION, MORPHOLOGY, AND MECHANICAL PROPERTIES,

摘要

Supercritical carbon dioxide (scCO_2) was added during compounding of polystyrene (PS)/poly(ethylene-methyl acrylate) copolymer (SP 2207) and poly(methyl methacrylate) (PMMA)/SP 2207 blends and the resulting phase inversion, morphology, and mechanical properties were studied. SP 2207 is a 80 wt.% ethylene-20% methyl acrylate copolymer used to increase the toughness of polystyrene and PMMA. Carbon dioxide was added at 2.0 wt.% based on polymer melt flow rates. Carbon dioxide injected into the extruder sped up the phase inversion of the two components by reducing the glass transition temperature of PMMA and PS. This allowed for an enhanced dispersion of the rubber phase after phase inversion. An earlier extruder location at which phase inversion occurred along with a reduced viscosity ratio greatly improved the dispersion of the rubber copolymer in the polystyrene and PMMA matrix. An increase in impact strength and a reduction in the flexural modulus of blends prepared with CO_2 were measured, indicating that CO_2 aided in dispersing the rubber into the brittle matrices of polystyrene and PMMA. Reprocessing did not result in a loss of morphology for PMMA/SP 2207 blends.