Experimental study and modeling of oscillating flow of high density polyethylenes

The influence of flow rate and die geometry on the observable flow rate/pressure relationship of a linear high density polyethylene is investigated using a capillary rheometer. The experimental results are applied to an adapted version of the relaxation-oscillation model proposed by Molenaar and Koopmans for describing the oscillating flow regime. The current model allows for a quantitative description of the hysteresis cycle in the oscillating flow regime in terms of the main experimental variables, such as imposed flow rate, reservoir (barrel) volume, and material compressibility. (C) 1996 Society of Rheology.