The measurement of extrudate swell is best as a qualitative measure of flow behaviour, although attempts to correlate it with fundamental rheological properties have been attempted. The measurement of extrudate swell of polymer melts using capillary extrusion rheometers is specified by the standard ISO 11443. An intercomparison of extrudate swell measurements using a high density polyethylene indicated that the reproducibility of results was poor. This was not entirely unexpected due to the differences in the procedures used by the laboratories, but is an indication of the difficulty of such measurements.

NPL Facility: Measurement of extrudate swell and draw down using either a capillary extrusion rheometer or a melt flow rate instrument.