| Polyproylene is one kind of crystalline polymer, whose suitable processing temperature is limited within narrow zone. What's more, the melt strength is low. All the factors above make it very difficult to form foaming product, though compared with other foaming plastic, even at 120℃, it can still keep its good mechanical properties and service performance, as well as its environment friendly property. So countries across the world attach great importance to polypropylene foaming.Using supercritical fluid carbon dioxide as foaming agent, on the basis of tandem extrusion equipment, the influence of processing conditions on polypropylene/carbon dioxide's foaming performance is studied, as well as the influence of different equipment. Major work includes: establishing two extrusion experiment system, one is twin-screw extruder complied with melt pump, the other is twin-screw extruder complied with single-screw extruder; evaluating the two extrusion system. Experimental results show that compared with twin-screw extruder & melt pump, twin-screw extruder & single-screw extruder is more suitable to polypropylene foaming. What's more, non-isothermal simulation about a section of spiral is performed by FEM Polyflow, and the influence of screw revolution speed,melt flux and barrel temperature on foaming performances of PP/CO2 is studied. Simulation results show that, in order to achieve uniform melt temperature, the revolution speed of sing-twin extruder should be limited with 30rpm～40rpm; barrel temperature should be 150℃; the depth of spiral should be about 2mm, and temperature difference should be about 2℃. At last, the author discusses how to select cooling equipment of barrel when using single-screw extruder as the second part. Temperature of cooling oil,flux of oil temperature controller,temperature difference between inlet and outlet of single-twin extruder are derived by heat transfer theory, which can also be expressed by mathematical equation.
|
PDF Full Text Request