The melt flow rate is a measure of the rate of extrusion of molten thermoplastic resins by means of an extrusion plastometer. Knowledge of the melt flow rate of a thermoplastic polymer gives the certainty that the material can be used safely and reliably in the field.
Melt flow rate testing of thermoplastic polymers is particularly useful in quality control to verify in-house materials or to quality check entrance materials. Melt flow rate testing is also a valuable tool to compare new materials in a product development setting (thermal stability and molecular weight comparison), or as part of full failure investigations.
The melt flow rate test moves the molten material at a single flow rate, therefore a single shear rate, and fails to capture the full range of the behavior of a material as a function of changing shear rate. To make matters worse, the shear rate is not even controlled. While the load on the material, or the shear stress, is constant during the course of the test, the shear rate is an output of the test. The MFR itself is a reflection of the shear rate used during the course of the test, but it is a result of the test and not a controlled input.
