Test EquipmentShear viscosity measurements of polymer melts using injection molding machine with adjustable slit die

Rheological properties of polymer melts were studied using a slit die attached to an injection molding machine. The die has three exchangeable inserts to set the slit height to 0.75, 1.0, or 1.5 mm. The modular design eases the die cleaning, and measurements with variable slit heights enable the detection of possible wall slip. Two grades of polypropylene and two grades of polystyrene were studied using the slit die and the results were compared to those obtained using a capillary rheometer and a rotational rheometer in steady and dynamic modes. The examination of the selected polymers with different slits gave essentially the same results at each slit height, verifying the absence of wall slip. The agreement with the conventional off-line rheometer results was very good for all polymers studied. This suggests that a simple slit die construction can be used as an inexpensive rheometer to measure rheological properties of polymer melts for processing purposes. The thermo-mechanical history of the investigated melt in the in-line slit die experiments resembles that in actual melt processing and, therefore, determination of rheological properties under true processing conditions is possible.