This test measures the melt flow curve of a PET sample at 3 temperatures and 8 shear rates.
A resin sample is dried overnight to remove residual moisture. The test is run by quickly packing the rheometer melt chamber at a predetermined temperature with the dried PET sample under a stream of nitrogen. After a preset heat soak time, the capillary rheometer is started at a defined speed, causing the resin to be pushed through a small orifice. The force required to make this happen is recorded. Once all the sample has been pushed through the orifice, the melt chamber is cleaned and reloaded from the same sample lot. Eight different shear rates are evaluated for each temperature with at least two replicates completed to verify accuracy at a given temperature. The correlation between the shear rate and viscosity may be used to determine the zero-shear viscosity using the “Modified Cross” relationship.
Additional temperatures may be evaluated by choosing the MFCadd test. For standard testing, only 3 temperatures are evaluated.