The Development Of Plastics Extrusion Foaming Visualization Experimental Apparatus And Research Of PS/supercritical CO₂ Extrusion Foaming

Foamed plastics have already been widely used in many fields because of their high specific strength, light weight good cushioning property and acoustical insulation. When cell diameter of the foamed plastics is within 0.1~10μm and cell density is larger than 109 / cm3 the foamed plastics will be called for microcellular foamed plastics, different from ordinary foamed plastics, microcellular foamed plastics can improve the impact toughness of the material significantly due to the passivation effect of pore size on crack growth. Supercritical fluid physical foaming agent assisted extrusion foaming process is a main industrial production method of foamed plastic for the characteristics of continuity, high production efficiency and environmental benign. In extrusion foaming process, the cell nucleation and growth occur in the channel of extrusion die, but the extrusion process is an invisible "black box".For further understanding of the extrusion foaming theory, this paper first designed a twostage screw which had three sections in each stage for amorphous polymer extrusion foaming process according to Tadmor melting theory. The screw had scraping pins and "pineapple" mixing head, and the strength of the screw was checked; then designed a visualization extrusion die according to the theories of mold design and simulated the flow of polystyrene melt in the die; finally the visualization experiments were carried out with the visualization extrusion system.The experiment captured the nucleation and foaming course within the melt, and the quality of products can be improved effectively according to the principle of cell evolution during the industrial production. Experiment results showed that: In the extrusion foaming die channel, the pressure of foaming onset point was depended on the extrusion backpressure instead of a constant; Under the condition of different screw speed, the variation of cell density and diameter fitted the prediction of classical nucleation theory; The shear stress field in melt can break larger cells and improve the cell density, reduce the cell diameter. Finally the relationship between the visualization results and the structure of the products was established by using scanning electron microscopy to characterize the structure of cell in the extrusion foaming products.