Extrudate swell ratio characteristics of CaCO3 added linear low density polyethylene

Four CaCO3 added LLDPE polymer systems were compounded in a 24 mm diameter, co-rotating, closely intermeshed twin-screw extruder. The compounds differed from each other by the weight percent of CaCO3 added. A laser beam system installed at the die exit of a capillary rheometer was used to determine the diameter of the swollen extrudate. Extrudate swell ratio, B∗, was found to decrease with increasing temperature, L/D ratio of the capillary die and the weight percent of the added CaCO3. Increasing apparent shear rate was, however, seen to cause B∗ to increase. An empirical correlation for predicting extrudate swell ratio was developed at apparent shear rates similar to those found in industrial processing conditions. The validity of this correlation was verified by measuring the extrudate swell ratios of the same polymer systems on a 36 mm diameter twin-screw extruder.