| In this work, high density polyethylene （HDPE） blending with low density polyethylene （LDPE） in a mass ratio of 7:3 were used as the raw materials, the supercritical carbon dioxide （scCO2） as the physical blowing agent, and the nucleation effect of different nucleating agents was systematically studied by extrusion foaming. The results of foam, the rheology characterization, the solubility and diffusivity of CO2 in composites and the crystal properties of polymer were used to analyze the effect of foam. The composite contained with 1.0wt% PVAc and 1.0wt% talc foamed best with the average cell size of 254 μm, cell density of 6.60×104 cells·cm-3 and expansion ratio 6.02.PE composites was used for extrusion foaming with scCO2. The result showed that the proper die temperature kept the melt in the range of suitable shear viscosity, which helped to get good cell morphology. As the gas inlet increasing, the expansion ratio of PE foams increased linearly, as well as the cell size decreased. When the gas inlet was 0.8 mL·min-1, the cell size was smallest; when the gas inlet was higher than 1.2 mL·min-1, the cells got merged, and the flow was unstable with a much higher gas inlet. The shear viscosity was calculated by capillary rtheometer. It was shown that shear viscosity decreased when temperature and gas inlet increased. And shear thinning was more obvious as shear rate rose. With process optimization, the liner PE foams were produced with the apparent density of 0.163 g·em-3, cell density of 6.17×104 cells·cm-3 and average cell size of 217.5 μm. |
