(136e) Microcellular Foaming of Pp/Pe Blends with Different Viscosity and Elasticity

Plastics foam is used in many engineering fields because of its low density and high impact resistance. There are still many difficulties in the foaming process, especially in controlling the cell morphology. It was found that polymer viscoelasticity has a great influence on the foaming process and cell morphology. In this study, the blends of polypropene (PP) and four grade polyethenes (PEs) were selected to investigate the effect of viscoelasticity on the foaming process. Blends were prepared using twin-screw extruder. The shear viscosities of pure polymers and the blends were measured using Haake on-line rheometer, before blending and during blending, respectively. The parison-swell was measured in order to characterize the elasticity of blends. Then, blends were used to foam in the high-pressure vessel with a quick-depressurizing valve. Two foaming pressures, 15 and 19 MPa, were selected to foam for all blends. The microstructures of the foamed blends were investigated using scanning electron microscope (SEM). The volume expansion ratio, average cell diameter, and cell density of foams were calculated. The results showed PEs with both higher and lower melt index had a negative effect on cellular structure and the volume expansion ratio, compared the PEs with moderate melt index. In addition, the higher the foaming pressure, the higher the volume expansion ratio, though cellular structure at higher foaming pressure was not favorable.