Rheology studies of two-phase gas-polymer suspensions during mold filling

In thermoplastic foaming, phase separation (i.e., bubble nucleation and growth) occurs due to a sudden change in pressure during mold filling that has significant effects on the rheology of polymer flow. An instrumented mold cavity has been designed to capture Theological measurements of the eventual two-phase gas-polymer suspensions. Experimental results for low density polyethylene (LDPE) and thermoplastic polyolefin (TPO) with two types of chemical blowing agents indicated that the rheological properties of two-phase gas-polymer suspensions were sensitive to shear rate, blowing agent concentration, melt temperature and mold temperature. The viscosity of gas-polymer suspensions was reduced in the presence of gas bubbles. A model has been proposed that yields good agreement with our experimental results for estimating the viscosity of two-phase flow in the mold cavity of the injection molding machine.