What Is the Polymer Melt Flow Index (MFI / MFR) to Viscosity Calculator?
The Melt Flow Index (MFI) measures the mass of molten thermoplastic polymer (in grams) extruded in 10 minutes through a standardized capillary die (diameter 2.095 mm, length 8.0 mm) under a prescribed deadweight load at a specified temperature.
Because MFI is inversely related to molecular weight and melt viscosity, higher MFI indicates lower viscosity and easier flow.
How Does the Polymer Melt Flow Index (MFI / MFR) to Viscosity Calculator Work?
Low MFI (< 1.0 g/10 min): High molecular weight, tough mechanical properties, suitable for blow molding and pipe extrusion.
Medium MFI (2 to 10 g/10 min): Balanced properties for general extrusion and sheet thermoforming.
High MFI (> 15 g/10 min): Low viscosity, ideal for high-speed thin-wall injection molding.
Polymer Melt Flow Index (MFI / MFR) to Viscosity Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Shenoy-Saini rheological correlation converting capillary extrusion rate under constant deadweight into dynamic melt viscosity.
How to Use the Polymer Melt Flow Index (MFI / MFR) to Viscosity Calculator
- Enter the resin manufacturer datasheet MFI value.
- Select the test load (default 2.16 kg) and polymer melt density.
- Read the estimated zero-shear dynamic viscosity in Pa·s.
Step-by-Step Example Calculation
Injection Molding Polypropylene Grade with MFI = 12
Input Values:
Understanding Your Result
Viscosity represents low-shear plateau viscosity; at real processing shear rates (1000+ s⁻¹), shear-thinning further drops viscosity by a factor of 10 to 50.
Factors That Affect the Result
- Temperature: MFI is tested at standard temperatures (e.g. 190°C for PE, 230°C for PP). Comparing MFI across different test temperatures is invalid.
When Should You Use This Calculator?
- Selecting raw resin grades for specific manufacturing processes (extrusion vs. injection molding).
- Quality control screening of recycled post-consumer regrind.
Assumptions & Limitations
- Provides order-of-magnitude estimation; precise mold filling requires capillary rheometer viscosity curves.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Based on empirical Shenoy & Saini polymer correlation.