What is unit of MFI?
The melt flow index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the weight of polymer in grams flowing in 10 min through a die of specific diameter and length by a pressure applied by a given weight at a given temperature.
What are the units of melt index?
Originally called Melt Flow Index or Melt Index (typically for polyethylene, but applied to a variety of materials), the standard designation today is Melt Mass-Flow Rate or MFR, which is a mass flow expressed (SI units) in g/10min.
What is the relation between MFI value and viscosity?
MFI values are meant to be inversely proportional to the viscosity of the plastic at the given conditions of the test. The higher the MFI value, the lower the viscosity is supposed to be.
How is melt flow rate calculated?
A weight specified for the material is applied to a plunger and the molten material is forced through the die. A timed extrudate is collected and weighed. Melt flow rate values are calculated in g/10 min. melt flow rate = g/10 min.
What is the difference between melt flow rate and melt index?
The Melt Flow Index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight.
What is the formula of MFI test?
The formula to Calculate MFI: MFI = Weight of sample in grams/ 10 min.
How do you interpret a melt flow index?
Melt Flow Indexer Melt flow indices are often listed on data sheets of thermoplastic materials. In general, a higher MFI indicates a lower material viscosity, and when comparing polymers of the same class, a lower melt flow rate corresponds to a higher molecular weight and/or less branching.
What is melt viscosity?
1 Melt Viscosity. The melt viscosity of a polymer at a given temperature is a measure of the rate at which chains can move relative to each other. This will be controlled by the ease of rotation about the backbone bonds, i.e., the chain flexibility, and on the degree of entanglement.
What is melt mass-flow rate?
The Melt Mass-Flow Rate is a one number indication of the viscosity of a polymer in the melt phase. It is defined as the mass of polymer in grams flowing per 10 minutes through a capillary of specific diameter and length by a pressure applied via a range of standard weights at specified temperature.
What material property significantly affects the melt flow rate?
Flow rate in a polymer is related inversely to viscosity. High-viscosity materials flow with greater resistance and therefore more slowly under any particular set of conditions than low-viscosity materials do. Therefore, higher-MW polymers have lower MFR values and lower-MW polymers have higher MFR.
What is a melt test?
Melt flow testing is simply a measure of the flow of a polymer when melted. The result of a melt flow test, called the melt mass-flow rate (MFR) or melt volume-flow rate (MVR), is defined as the amount of mass or volume of a polymer that flows through a small die at a specified temperature and pressure.
What is melt mass flow rate?
How is the melt flow index related to viscosity?
Melt flow index. At the same time, melt flow rate is a measure of the ability of the material’s melt to flow under pressure. Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, though it should be borne in mind that the viscosity for any such material depends on the applied force.
Is the melt flow index a good measure of the processing window?
However MFI takes no account of the shear, shear rate or shear history and as such is not a good measure of the processing window of a polymer. It is a single-point viscosity measurement at a relatively low shear rate and temperature.
When does viscosity of a polymer melt decrease?
POLYMER MELTS THE VISCOSITY DECREASES AS THE SHEAR RATE (du/dy) INCREASES (due to molecular alignments and disentanglements) A characteristic value is the limiting viscosity for zero shear rate (frequently referred to aszero shear viscosity) usually denoted with η
Why is the melt flow rate test important?
This illustrates the usefulness of the MFR test in providing a relative measurement of the average MW of a polymer. Because the MFR test is performed at relatively low shear rates, the results approximate the zero-shear viscosity, despite the fact that the shear rate is not controlled.