Research On Effect Of Blending On Polypropylene Extrusion Foaming

Polypropylene is linear semi-crystalline polymer, with low melt strength, narrow molecular weight distribution and narrow temperature range. Research on PP extrusion foaming is mainly on how to improve its properties. Crosslinking modification is more used than blending, and research on the effect of resin rheological properties on foaming is rare.First, three linear co-polypropylene with different molecular weight were chosen as matrix resin, marks of which are M02, SP179, RS1684respectively. From the aspects of structure, rheological properties of matrix resin,a preliminary discussion was carried out, which was regarding to the suitable structure features of polypropylene used in extrusion foaming. The results showed that among three types of polypropylene resin, the one with higher molecular weight had higher melt viscoelasticity. So, in the stage of bubble growth, M02was able to bear tensile stress exited in the bubble expanding process, and prevented bubble from rupture and coalescence;furthermore, in the stabilization stage, M02was able to guarantee steady growth of bubbles. At last, foam material with small size and good uniformity was obtained, apparent density was0.08g/cm3, minimum cell diameter was93.7μm, cell density was4.5×106cells/cm3.Second, the effect of HMSPP content on foam sample’s properties was studied. The results showed that apparent density was0.278g/cm3with10%HMSPP content, and apparent density was0.09g/cm3when the content increased to30%.Third, in order to broaden temperature range, M02was modified by addition of LDPE, LLDPE, HDPE, and the crystallization and rheological properties of PP/PE blends were tested. Then, combining with properties of foam material, the influence of PP/PE blends on bubble growth and stabilization was studied. The results showed that temperature range was not broadened, but crystallization temperature was higher and crystallization rate was quicker. And viscosity and elasticity of PP/20%-HDPE blend was higher, and nucleation sites of which were more, so the foam sample of PP/20%-HDPE blend was better. The cell diameter was67μm, apparent density was0.04g/cm3.At last, the influence of die size on the properties of polypropylene foam was studied. The results showed that lower apparent density and cell diameter was obtained with lower hight of die size.