The melt flow index (MFI) of PET (polyester plastics) is usually low because it is prone to degradation at high temperatures. PET is typically used in fibers, bottle flakes, or films rather than conventional melt processing methods such as injection molding. However, certain modified PET grades (e.g., injection molding grades) have specific MFR ranges:

1.Regular PET (unmodified)

Fiber/film grade PET: MFI is usually not measured directly (as its processing methods are mostly melt spinning or extrusion stretching).

Bottle grade PET: MFI is extremely low (around 0.1–1 g/10min, but it is typically measured by intrinsic viscosity [IV], such as 0.70–0.85 dL/g).

2.Injection molding grade PET (modified)

Reinforced PET (e.g., glass fiber-filled): MFI is approximately 10–50 g/10min (tested at 280°C with a 2.16 kg load).

Fast-crystallizing PET (for engineering parts): MFI ranges from 5–30 g/10min.