calculating viscosity from melt flow index

An MFR measurement can be produced within 25 minutes and often considerably less, depending on the polymer. There is good reason for this approach, not least because measuring melt viscosity requires a substantially more complex technique, involving more costly instruments and, probably of most importance, more time. Melt Mass Flow Rate Measurement It is important to appreciate that an MFR value is not a measurement of viscosity but is indicative of it MFR is measured in g/10mins and viscosity in Pas, so MFR is, in fact, a mass flow rate. There are two principal MFR standards ISO 1133 and ASTM D1238.

No mention of MFI is present in the ISO standard consequently, in this article, only the term MFR will be used, and the standard referred to will be the ISO version.

However, for all other materials, the use of melt index or any term other than “flow rate” is discouraged, regardless of the condition used’. The ASTM standard acknowledges this potential confusion in its note 27 thus, ‘It has become customary to refer to the flow rate of polyethylene as “melt index” when obtained under Condition 190/2.16. This seemingly semantic change is important because the term MFI is still widely used today, so any practitioner will encounter it regularly when, in official terms, it should only ever be referred to as MFR. However, both standards have superseded this by melt mass flow rate, or MFR. In the early days of the measurement, the term most often used was melt flow index or simply MFI. The measurement is performed in a standardised manner, with the two recognised incumbents being the European ISO standard and the American ASTM equivalent. Due to its simplicity and accuracy, it forms the basis of many companies' incoming quality control programmes. The method has been in use for many decades, having originated in the ICI laboratories following the commercial development of polyethylene in the 1930s. Melt mass-flow rate is an industry-standard method used to quickly gain a feel for the viscosity of a polymer in its melted state, which is the state in which most thermoplastics are formed into useful products.

Calculating viscosity from melt flow index