Melt Flow Index to Viscosity Calculator
Rheology & polymer processing: Convert ASTM D1238 / ISO 1133 Melt Flow Rate (MFI/MFR) to apparent capillary shear stress, shear rate, zero-shear viscosity, and Mw.
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Frequently Asked Questions
Why is Melt Flow Index (MFI) inversely proportional to molecular weight?
MFI measures how many grams of molten polymer extrude through a standard capillary die in 10 minutes under a fixed load. Longer polymer chains have greater macromolecular entanglement, dramatically increasing melt viscosity (η₀ ∝ Mw³.⁴). Therefore, high molecular weight resins flow sluggishly, resulting in low MFI values.
At what shear rate does the standard melt index test operate?
Under standard 2.16 kg test load conditions, the wall shear rate inside the 2.095 mm capillary die is quite low, typically ranging from 1 to 50 s⁻¹. In contrast, industrial injection molding operates at much higher shear rates (1,000 to 100,000 s⁻¹), where pseudoplastic shear-thinning reduces apparent viscosity by orders of magnitude.
What is the significance of a "fractional melt" resin (MFI < 1.0)?
Polymers with an MFI below 1.0 g/10 min are known as fractional melt resins. They feature high melt strength, high tensile toughness, and excellent Environmental Stress Crack Resistance (ESCR), making them the industry standard for extrusion blow molding of chemical drums and pressure pipes.