Supercritical fluid assisted polymer blending

The blending of immiscible polymers offers processors the opportunity to create materials with a wide range of properties that include improved processing and end use capabilities. A method for blending immiscible polymers with the addition of supercritical carbon dioxide has been investigated.; The viscosity ratio of polymer melts is an important parameter influencing polymer blending. It can affect morphology development, phase inversion, mechanical properties, and product quality. It is desirable to blend immiscible polymers that have similar melt viscosities. Carbon dioxide can act to lower the melt viscosity of various polymer melts thus lowering the viscosity ratio.; The blend systems studied in this work were PMMA/polystyrene, polystyrene/SP 2207, and PMMA/SP 2207. An improvement in blend morphology was observed for each blend that was processed with the injection of CO₂ into the twin screw extruder barrel. The injection of CO₂ into the polymer melts lowered the viscosity of PMMA by 80%, polystyrene by 64%, and SP 2207 by 50%. This allowed for the viscosity ratio to become closer to one. The viscosity ratio, ηPMMA/ηpolystyrene, was reduced from 7.3 to 3.4 upon CO₂ injection. The viscosity ratio, ηPMMA/ηSP 2207, was reduced from 15.5 to 3.5 upon CO₂ injection. The viscosity ratio, ηpolystyrene/ηSP 2207, was reduced from 2.53 to 1.3 upon CO₂ injection. As a result, the domain size of the dispersed phase decreased.; The injection of CO₂ into a twin screw extrusion process acted to shorten the length of the machine required for phase inversion. For both, polystyrene/SP 2207 and PMMA/SP 2207 blends with and without the injection of CO₂ the extruder length for phase inversion was shortened by an L/D = 4, or 10% of the total extruder length.; The addition of CO₂ increased the impact strength and lowered the flexural and tensile modulus relative to the same blends prepared without the addition of CO₂. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26.1% by the addition of CO₂. The flexural and tensile modulus were decreased by 42% and 25% respectively upon CO ₂ injection into the extruder. The improvement in impact strength was not as large for blends of PMMA and SP 2207.