Melt Flow Index

property

A measure of the ease of flow of thermoplastic materials under standardized conditions, expressed as grams of polymer extruded per 10 minutes through a specific die at controlled temperature and load.

In Simple Terms

Think of MFI as a plastic's 'flowability rating.' Higher MFI means the plastic flows more easily when melted, like thin honey versus thick molasses. This helps processors choose the right resin grade for their specific molding or extrusion application.

Why It Matters

MFI directly impacts processability, cycle times, and part quality. Resin traders use MFI to match customer requirements, while processors rely on it to optimize temperatures, pressures, and speeds. Consistent MFI ensures predictable manufacturing outcomes.

Technical Details

MFI is measured per ASTM D1238 using a melt flow indexer at specified temperature and load conditions. Common test conditions include 190°C/2.16kg for polyethylene and 230°C/2.16kg for polypropylene. The measurement correlates inversely with molecular weight - higher molecular weight resins typically exhibit lower MFI values.

Real-World Examples

HDPE blow molding resin selection

A bottle manufacturer specifies HDPE with MFI 0.3-0.7 g/10min for optimal parison strength and processability in large container production.

Polypropylene injection molding grades

Thin-wall packaging applications require PP with MFI 20-40 g/10min for fast cavity filling, while automotive parts use MFI 8-15 g/10min for balanced flow and strength.

Quality control in resin trading

Colorado Sun Inc verifies each lot's MFI matches the certificate of analysis within ±15% to ensure consistent processing performance for customers.