MFI / MFR (melt flow index)

Melt flow index measures how many grams of molten polymer flow through a standard die in ten minutes under a set load and temperature (190 °C/2.16 kg for PE; 230 °C/2.16 kg for PP). It is the inverse shorthand for molecular weight: high MFI flows easily (injection moulding), low MFI resists (blow moulding, film — where melt strength matters).

Working ranges in this trade: rHDPE blow 0.3–0.7 g/10 min, rHDPE injection 4–8, rLDPE film 0.3–2.0, rPP 4–25 by application. For recyclates, MFI also diagnoses history — degradation from repeated processing usually raises PE and PP flow — so a stable MFI lot-to-lot signals a controlled feedstock. Always quote MFI with its test condition; a number without the temperature and load is not a specification.