What Is MFI (Melt Flow Index) and Why Does It Matter?
MFI is a fundamental value showing the flowability of a polymer in its molten state. The correct MFI selection determines quality in your injection and extrusion processes.
MFI (Melt Flow Index) is a value that measures, in grams, how much a thermoplastic flows in 10 minutes under a specific temperature and load. It is usually expressed in g/10 min and provides a quick indicator of a polymer's processability.
What Does MFI Represent?
A high MFI value means the polymer is more fluid (lower viscosity), indicating that the melt spreads easily within the mold. A low MFI means higher molecular weight and a more viscous melt. As molecular weight increases, mechanical strength generally improves but flowability decreases.
Relationship with Process Selection
- Injection molding: High-MFI (fluid) grades are preferred for thin-walled and complex parts.
- Extrusion: Low-MFI (viscous) grades provide melt strength for pipes, profiles and film.
- Blow molding: A medium MFI is ideal for parison strength.
Why Is It Critical?
Incorrect MFI selection can lead to defects such as short shots, flash, sink marks or poor mechanical performance. Additionally, in recycled raw material, MFI consistency is one of the most important indicators of batch quality.
At SNC Plastik, we supply raw material grades with the MFI value suited to your process, along with their technical data sheets, and provide engineering support for the right selection.