Research On The Foaming Behaviour Of Polypropylene And The Modificated Materials With Chemical Foaming Agent And Supercritical CO₂

Foamed polypropylene will be used widely in many fields such as packing, automobiles, buildings, communications and other fields, because of its excellent performance, good thermal stability, impact resistance, chemical resistance, oil resistance and higher strength and stiffness, and it can be recycled many times, so it is a kind of environment-friendly foaming material, and it gradually tends to replace the other foamed materials.The foaming of polypropylene is difficult, because temperature increasing beyond the meltpoint, the melt strength of PP sharply declined, the cover ability of melt declined, causing bubble hole collapse, and it’s difficult to produce qualified foam products.Therefore, the modification of PP, and the preparation of the high melt strength polypropylene is the key point of resolution to the technology of PP foam materials.First, in this paper to use polypropylene (T30S) as raw material, and compare the foaming behavior using the conventional chemical foaming agent and batch foaming process with super critical carbon dioxide (scCO2). The morphology, cell structure, cell diameter, and cell density, foaming rate of foam products were determined by Using the scanning electron microscope (SEM) and optical microscope. Without adding any additives in the foaming process, uniform rules, cell structure and appearance of the product integrity, foaming and high cell density, foaming rate remains at3~10times, maximum foam may reach about15times, so it indicated that batch foaming process with super critical carbon dioxide (scCO2) is better than two steps foaming processes with chemical foaming agent. Is discussed on the basis of this infiltration of different temperature, time, processing time, pressure releasing speeds issued expansion ratio and cell structure changes. So as to determine the best conditions of foaming technique:196~204℃temperature and pressure:15~20MPa.Second, using the high melt strength polypropylene (HMSPP) as raw material, under the same process, using batch foaming process with super critical carbon dioxide (scCO2) to get foam products from PP and HMSPP, and comparing them. Results showed that through the naked eye observation, HMSPP foam beads the size of regular, uniform-density and high foaming rate, a maximum of about30times. And its foaming effect is significantly better than the foaming effect of T30S.Finally, in order to improve the melt strength of PP (T30S), mixing Nano-SiO2(granular), mica (sheet), basalt fiber and ABS to modify PP. At the same time, using the batch foaming process with super critical carbon dioxide (scCO2) to study the foaming behavior of the modified product. The melt strength of granular material was modified by RLS melt flow rate tester. Finding that blend improved melt strength, and ABS works best, improving by a factor of about3times. Observing the foam products from batch foaming process with super critical carbon dioxide (scCO2) by SEM, finding that PP foaming materials of foam density, uniformity is significantly improved with the addition of fillers.