Study On Optimization Of Injection Molding Process And Enhancement Mechanism Of Microcellular Foam Polypropylene

Polypropylene has a low density?about 0.94 g / cm3?,high strength,a certain impact resistance,the advantages of cheap,so that its application is extremely broad.In this essay,we mainly optimize the microcellular foamed polypropylene injection molding process and the enhanced mechanism of the tensile properties of polypropylene foam.?1?The optimal injection molding process of the old injection mold is: 1.The optimal combination of the tensile strength: the nozzle temperature is 180?C,the injection pressure is 30 MPa,the injection speed is 25 mm / min,the packing pressure is 30 MPa,the cooling time For 15 s.2.The optimal combination of impact strength: nozzle temperature of 180?C,injection pressure 40 MPa,injection speed of 15mm/min,packing pressure of 40 MPa,cooling time of 15 s.The tensile strength of PP after foaming is 36.5MPa,the impact strength is 41.4KJ/m2,the tensile strength of pure PP is 37.2MPa,the impact strength is 35.7KJ/m2.?2?Using 5 parts of ultra-fine NaHCO₃ as a blowing agent,the new injection mold in the optimal injection molding process: 1.The optimal combination of tensile strength: the nozzle temperature is 185?C,the injection pressure is 50 MPa,the injection speed is 40 mm / min,the packing pressure is 60 MPa,the packing time is 20 s.The tensile strength of the extruded spline was 43.1 MPa,while the tensile strength of pure PP was 39.8 MPa.2.Impact strength: The nozzle temperature is 185?C,the injection pressure is 50 MPa,the injection speed is 40 mm / min,the packing pressure is 55 MPa,the packing pressure is 25 s.Under this optimized condition,the impact spline is 63.5KJ / m2,while the impact strength of pure PP is 55.1MPa.The tensile strength of the polypropylene under 3 parts of the blowing agent was 43.6MPa,and the tensile strength of the stretched spline reached the maximum height of the universal tensile tester.The maximum impact of the polypropylene under 5 foaming agent Strength 63.4KJ / m2;3 copies of the bending strength of the largest,35.8MPa,9 copies of the bending modulus of the largest,1155 MPa.?3?POM,DSC and XRD showed that ultrafine Na2CO₃ was produced by the decomposition of ultrafine NaHCO₃ after adding 3 parts of blowing agent,which played the role of nucleating agent,which increased the nucleation point of PP.The nucleus generation rate is accelerated,the size of the spherulite decreases,the spherulite size is more regular.In addition,the presence of micropores also hinders the increase of spherulites.SEM revealed changes in the microstructures during the stretching process,and almost no change in the shape of the pores before yield,and did not have any effect on the properties of the PP-3.However,in the necrotic and strain hardening stages,the micropores are gradually oriented,and some microstructures break down to form larger voids.It is clear that they disperse the tensile stress,and the fibers are broken during the stretching process,so that the final breaking strength is improved.While reducing the stress concentration point.?4?There are some shortcomings in this research,adding refined NaHCO₃ for foaming,the apparent density of PP foam is relatively small and the improvement of mechanical properties is not prominent.In addition to the PP after the release of a period of time will turn yellow.