Supercritical Carbon Dioxide Assisted Modification Of PPO

PPO which is in the nature of good mechanical property, heat resistance and flame resistance has high strength and dimensional stability. What's more, its high-temperature creep resistance is the strongest of all engineering thermoplastics. However, its high glass transition temperature, high melt viscosity, poor mobility and poor processing molding have a serious impact on the application and promotion of PPO. The most important measure to resolve is blending modification to PPO. Because of the presence of the PPO benzene ring, PPO melt rheology behavior is poor. The PPO melting modification can't achieve by just using the twin-screw extruder, which need some aid. For most polymers, the supercritical carbon dioxide (SC-CO2) fluid is a good plasticizer, which can significantly improve the mobility of the polymer melt. Therefore, SC-CO2 is more and more applied in the modification of polymer blends. In this study, the SC-CO2 injection influence on rheology behavior, processability, mechanical property of the blends and the microstructure of the PPO/POE-g-MAH and PPO/HIPS blends was studied. A preliminary analysis has been done about advantages and disadvantages of SC-CO2 assisted PPO blends modification.The rheological behavior of PPO, POE-g-MAH and HIPS was studied with the slit die rheometer and online rheological testing systems. The results show that adding SC-CO2 can reduce shear viscosity. With the increase of SC-CO2 injection, PPO shear viscosity reduction rate increases. Compared with no gas injection, PPO shear viscosity decreased by 36.7% when the SC-CO2 addition was 4wt%, and shear rate was 120s-1. SC-CO2 injection has different effect on the viscosity reduction to the PPO, POE-g-MAH and HIPS, and PPO viscosity reduction effect is the most significant. Therefore, SC-CO2 injection can reduce the viscosity ratio of PPO blends. Compared with no gas injection, PPO/POE-g-MAH blends shear viscosity ratio decreased by 15.7%, and PPO/HIPS blends shear viscosity ratio decreased by 13.2% when the SC-CO2 addition was 2wt%, and shear rate was 120s-1. Viscosity ratio reduction can help to have dispersed mixing.The extruder melt pressure, torque and specific energy consumption changes were collected and analyzed by using self-developed online data acquisition system at the time of SC-CO2 assisted PPO blends modification. The results show that SC-CO2 injection helps to reduce the melt extrusion pressure, torque and specific energy consumption of PPO blends. With the increase of SC-CO2 injection, the decline of melt pressure, torque and specific energy consumption increases. Compared with no gas injection, the maximum reduction of melt pressure was 33.5%, the maximum reduction of extruder torque was 10.77% and the maximum reduction of specific energy consumption was 16.63% when the 4wt% SC-CO2 was injected to PPO/POE-g-MAH blends.There was a mechanical performance test for the sample which was got by SC-CO2 assisted PPO blending modification. The microstructure of the PPO blends was inspected by SEM. The results show that adding SC-CO2 makes the PPO blends impact strength increase, tensile strength of blends decrease and elongation decrease. Compared with no gas injection, PPO/POE-g-MAH blend impact strength which was 79MPa increased by 85.6%. PPO/POE-g-MAH blends tensile strength decreased by 5.3% when the SC-CO2 injection was 2wt%. The addition of SC-CO2 helps to achieve dispersed mixing. The mean grain size of blends dispersed phase declined, particle size distribution width index narrowed down.Compared with no gas injection, PPO/POE-g-MAH (950:50) blends dispersed phase size which was 0.125um increased by 43.8%, and particle size distribution width index decreased by 20.7% when the SC-CO2 injection was 3wt%.There was a simple analysis of the influence about vacuum to extrusion pressure, extruder torque, specific energy consumption, the mechanical properties and microstructure at exhaust section. The results show that compared with non-vacuum, the tensile strength and elongation increases, impact strength slightly declines, the blends melt pressure, torque and specific energy consumption increases, the dispersion average particle size increases, and the size distribution width index increases when there is vacuum in the exhaust section. But compared with no gas injection, impact strength increases, and the disperse phase average particle size declines.