On-line measurement of the PVT properties of polymer melts using a gear pump

This paper presents a newly developed experimental apparatus, based on an extrusion system, which can economically and accurately measure the pressure-volume-temperature (PVT) properties of polymeric fluids. The density or specific volume of a polymer melt is determined by measuring the mass and volume flow rates of the melt. A positive displacement gear pump mounted on an extruder is used to measure the volume flow rate of the melt. In order to reduce the leakage across the gear pump, the difference between the upstream and downstream pressures is minimized by using a variable resistance die attached to the downstream outlet of the gear pump. The positive displacement volume of a gear pump was determined in calibration experiments with water and oil with the aid of a syringe pump. Two critical sets of experiments were carried out to measure the specific volumes of polystyrene and polypropylene as case examples. The measured results were compatible with the known PVT data, confirming the validity of the system.