Experimental Investigation On The Forming Process Of Microcellular PMMA And PP Foams

Microcellular polymer as a new kind of "green" materials possesses excellent performance gaining more and more interests and studies in recent twenty years. Technology of preparation of microcellular polymer by using supercritical fluids has been commercialized. However, many fundamental problems involved in microcellular foaming technique and performance of products still remain undisclosed and indistinct, such as, the nucleation mechanism, the influence factors of cell structure and structure-performance of resulting products.Firstly, this thesis make an experimental investigation on the forming process and the influence of processing parameters on preparation of PMMA microcellular foams by using typical batch foaming process. We compared elevated temperature process and decompressed process by investigating the effects of foaming temperature, foaming time and saturation pressure. The resulting products are characterized from both micro- and macroscopic view point such as cell density, cell diameter, expansion ratio and apparent density.The experimental results indicate that there is an optimized processing window for temperature of elevated temperature process in which the resulting sample with maximum cell density, minimal cell diameter and high expansion ratio can be formed. For decompressed process, the sample with higher cell density and smaller cell diameter should be foamed under the low temperature and high pressure. Further more the pressure release rate should be as quick as possible.Secondly, microcellular PP foams have been studied by batch, extrusion and injection molding process. For batch process, the effect of elastomer content and different components on foaming process has been investigated. The relevant foaming mechanism is also discussed.In our study, we found it is difficult to get microcellular structure by extrusion process. The main reasons are come from processing parameters and rheological properties of material.Microcellular foamed PP has been produced successfully by injection molding process. It is up to the high pressure release rate during injecting process and the strong mixed ability of plasticizing system.