Measured in a melt indexer at a set temperature and load, for polypropylene 230 degrees C and 2.16 kg, it is the first number a spunmelt line checks on a new resin lot. Higher values mean lower viscosity: spunbond resins sit around 25 to 40 g/10 min, while meltblown resins run into the hundreds or past 1,000 so the air can draw fibers down to a few micrometers. A lot that drifts off spec changes filament breaks, shot and uniformity.
Melt flow rate on the new lot came in at 1,550, so expect more shot until we drop the die temperature.
Polypropylene breaks down in the extruder, so MFR on the fabric runs higher than on the chips; a big gap means too much heat or residence time.
Also heard as
- MFR
- MFI
- melt index
Related terms
PP
Polypropylene: the most widely used polymer in nonwovens, especially spunbond and meltblown fabrics.
Meltblown
Web of very fine fibers made by blasting molten polymer from a row of tiny die holes with hot, high-speed air.
Spunbond
Nonwoven of continuous filaments extruded, air-drawn and laid on a belt, then usually bonded by a hot calender.
Shot
Small beads or lumps of polymer that failed to form fibers and sit embedded in a meltblown web.