However, this test can be conducted practically at room temperature. Performing the IV test is more complicated because of the need for a delicate apparatus and the use of some very noxious chemicals. The greater the difference between these flow rates, the higher the IV of the material and the higher the average MW of the polymer. This test involves creating a dilute solution of the polymer in the appropriate solvent and then comparing the flow rate of this solution to the flow rate of the pure solvent through a piece of glassware of a standardized geometry. But instead of using MFR, the manufacturers of these materials have chosen to use intrinsic viscosity (IV). Amorphous PET, for example, does provide a value that is related to molecular weight (MW). But there are some polymers where the availability of a MFR value is inconsistent across the base of suppliers, and there are a few polymer families where a MFR value is rarely provided by any supplier. Virtually every grade of material within many polymer families provides this data point, and certifications will almost always list the MFR value for every lot. The number of commercial materials that employ a melt flow rate (MFR) value as part of the published property profile attests to the usefulness of the test.
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