Effects of Pressure and Supercritical Fluid on Melt Viscosity of Low Density Polyethylene (LDPE) in Conventional and Microcellular Injection Molding

摘要

In this study, the flow and Theological behaviors of low density polyethylene (LDPE) and single-phase LDPE/N_2 polymer/gas solutions at various gas contents are measured using a high-pressure slit-die rheometer. The resulting rheology data of LDPE and LDPE/N_2 are curve fit using the Cross-WLF model to obtain the seven material model constants, which were then used in simulation of conventional and microcellular injection molding processes. The pressure effect on the shear viscosity of LDPE is also studied. The pressure factor, D3, in the Cross-WLF model was determined by the use of simulation to best fit the experimental results. In addition, a three-dimensional plot of shear viscosity as a function of shear rate and pressure at various temperatures has been constructed. Based on this 3-D viscosity-shear rate-temperature-pressure plot, the increase in viscosity due to the pressure effect is more profound at high pressures, low temperatures, and low shear rates.