Polypropylene fiber and nonwoven resin: MFR by process, from raffia to 1,500 MFR meltblown

MFR windows by fiber process

Almost every fiber process runs PP homopolymer. Random copolymer shows up in soft and high-loft spunbond and some staple, and impact copolymer is rare in fiber. Every melt flow rate (MFR) on this page is at 230°C / 446°F, 2.16 kg, by ASTM D1238 or ISO 1133. A polyethylene melt index at 190°C / 374°F is a different test and does not compare. See what melt flow index means.

Typical published windows from producer fiber and nonwoven selection guides and data sheets. Grades are spaced by line type, denier and speed, so confirm on the data sheet for the grade you run and let a chemist check any equivalent before you switch.

How 1,500 MFR meltblown resin is measured

A standard melt flow test times or weighs the resin that flows through a die with a 2.095 mm (0.0825 in) bore. At 1,000 g/10 min and above, the strand runs out in seconds, so small timing and weighing errors become large ones.

ASTM D1238 handles this with Procedure C, an automatically timed test for polyolefins that uses a “half-die”: half the length and half the bore of the standard die, so the length-to-diameter ratio stays the same. The standard describes it as an alternative to Procedure B (the standard die, generally used up to about 1,500 g/10 min) for resins above about 75 g/10 min. It also says Procedure C results must not be assumed to be half of Procedure B results. In short, a half-die number and a standard-die number on the same resin are different numbers, with no simple factor between them.

Producers report meltblown MFR in different ways: by ASTM D1238 with the standard die, by the half-die procedure, by ISO 1133, and a few as a melt viscosity instead of an MFR. Two sheets that both say 1,500 can describe resins that run differently on your line.

Grades that still carry peroxide add a second question. The MFR rises as the peroxide reacts, in your extruder and also in the heated barrel of the melt flow tester, so the number depends on how the lab handled the sample. Ask how the COA value was measured and whether it is the final MFR the grade is designed to reach.

What to ask for: the standard and procedure (standard die or half die), temperature and load, the lot value and spec range on the COA, and for peroxide grades, whether the value is the final MFR. When you compare a second source, have one lab test both resins the same way.

Reactor, controlled-rheology and peroxide-coated grades

• Reactor grades. The MFR comes straight from the polymerization reactor. Ziegler-Natta reactor PP has a broader molecular weight distribution, which gives the melt strength tape, strapping and coarse staple need. Metallocene catalysts make a very narrow distribution in the reactor, and some meltblown grades reach their high MFR in the reactor rather than with peroxide. See metallocene PP.
• Controlled-rheology (CR) or visbroken grades. A lower-MFR reactor resin is extruded with a small dose of organic peroxide, which cuts the longest chains. MFR goes up and the distribution narrows. Narrow-distribution resin spins finer and more evenly, resists draw resonance and gives fewer breaks at high speed, at the cost of a little tenacity. Most spunbond, CF and BCF grades and many meltblown grades are made this way.
• Peroxide-coated or peroxide-masterbatch meltblown resin. Some meltblown resin is sold as lower-MFR pellets or granules coated with or carrying peroxide, and the visbreaking finishes in your extruder. Final MFR then depends on your melt temperature and residence time, so a change in extruder conditions can show up in the fabric, and peroxide breakdown products can add odor and spinning smoke. Ask for the final MFR at stated conditions, the producer’s storage and shelf-life guidance, and whether the grade suits your line.
• How producers label the distribution. Some selection guides mark grades narrow, medium or broad. Others give a polydispersity (Mw/Mn) or a rheology value. Match like with like, and when a sheet gives only MFR, ask how the grade was made.
• Why it matters in a swap. A reactor grade and a CR grade at the same MFR do not spin the same. The broader grade can break more at fine denier, and the narrower grade can neck in or lose melt strength in tape. Treat a switch between them as a new material, not a lot change. See PP homopolymer grades.

Ash, gels and filterability

Spinneret holes are a fraction of a millimeter wide, so fiber lines catch contamination a molder never notices. One gel or hard particle can break a filament, block a hole or push pack pressure up until the pack has to be changed.

• Ash. Catalyst residue and other inorganic material, by ASTM D5630 or ISO 3451-1. Fiber grades run very low ash. Ask for the ash spec, and a lot value if your line is sensitive.
• Gels and specks. Unmelted or crosslinked particles and black specks. Producers often count gels by size on a cast film strip. Ask how the grade is tested and what the limit is. See gels and fisheyes and black specks.
• Filterability and pressure rise. A filter test pumps melt through a fine screen at a fixed rate and records how fast pressure climbs. For color concentrates, the filter pressure value test (ISO 23900-5) reports the rise per gram of pigment. Results compare only on the same rig, screen and conditions, so your own pack pressure trend and pack life are the real check.
• Volatiles and smoke. Low-molecular-weight material and peroxide breakdown products can smoke at the die, build up on the spinneret face and add odor to hygiene products. Low-volatile grades exist for this reason.
• Pellets and conveying. Fines, streamers and angel hair from conveying lines melt unevenly and cause pressure spikes. Check the bottom of a gaylord before you blame the resin.

Additives: stabilizers, antistat, hydrophilic finish, electret, UV and color

• Process stabilizers. A phenolic antioxidant and a phosphite protect the melt through spinning. Each pass through an extruder uses some up, so reclaimed edge trim lowers what is left.
• Gas fading. Phenolic antioxidants can turn white fiber yellow or pink in storage near gas-fired heaters or engine exhaust, where nitrogen oxides react with them. Many fiber grades carry an anti-gas-fading (AGF) package for this reason. Put it on the RFQ for white and pastel fiber and hygiene nonwovens.
• Antistat. Static on spinning and carding lines is often handled by the spin finish, a topical treatment, rather than by the resin. Melt-added antistats come as masterbatch when needed.
• Hydrophilic finish is not in the resin. PP repels water. The wettable topsheet in a diaper or the absorbent layer in a wipe often gets a surfactant finish sprayed or rolled onto the fiber or fabric after spinning. Melt-additive hydrophilic masterbatches exist for some uses, but the base resin is still a natural fiber grade. Ask your finish or masterbatch supplier, not the resin producer, for wetting performance.
• Electret charge for filtration. Meltblown filter media is charged by corona or by hydrocharging so it traps fine particles at low pressure drop. How long the charge lasts depends on resin purity and on charge-stabilizing additives, which come as an electret masterbatch or, in at least one producer’s meltblown grade, built into the resin. Ask whether the grade is recommended for charging, and qualify charge decay on your own media.
• UV for geotextiles and agriculture. Unprotected PP fiber loses strength in sunlight within months. Geotextiles, silt fence, ground cover, shade cloth, twine and woven sacks need a UV package, most often a hindered amine light stabilizer (HALS) masterbatch, sometimes with carbon black. Highway specs built on AASHTO M 288 ask for at least 50% strength retained after 500 hours by ASTM D4355 (xenon arc) for most geotextiles and 70% for silt fence, and some state DOTs ask for more. See UV-resistant plastics.
• Color masterbatch. Use a fiber-grade concentrate on a PP carrier with an MFR close to your base resin (much higher for meltblown) and pigments that survive your melt temperature. Dispersion matters more than in molding, since agglomerates block screens and break filaments. Dose by weight, commonly about 1–4%, and ask for the concentrate’s filter pressure value. See masterbatch vs. precolored resin and custom color concentrate.

FDA, hygiene and medical paperwork

• FDA letter. For food-contact and many hygiene uses, ask for the producer’s letter for the exact grade. For PP it often cites 21 CFR 177.1520 (olefin polymers) and states conditions of use. Masterbatch and additives you add need their own letters. See FDA food-contact resin.
• Hygiene nonwovens. Diaper, feminine care and wipes brands often ask for an FDA letter, statements on intentionally added substances such as phthalates (some fiber grades are made on non-phthalate catalysts), and heavy metals, REACH and California Prop 65 statements. Collect these before the trial, since a brand owner’s approval can take longer than the trial itself.
• Medical nonwovens. Gowns, drapes, sterilization wrap and masks are regulated as finished products. Several producers’ data sheets bar medical device use unless the producer approves the application in writing, and bar implants outright. Tell us the end use up front so we only quote grades whose producer allows it. Biocompatibility testing such as ISO 10993 is done on the finished device. See medical and FDA grades.
• Masks and respirators. In the U.S., NIOSH approves N95 respirators as finished products under 42 CFR Part 84, and surgical masks are tested as finished masks to ASTM F2100. The resin supports those results but is not itself approved, so a resin change can mean retesting the mask.
• Change notification. If your customer requires notice of any raw material change, a second-source grade counts, even an equivalent one. Build that notice into the qualification plan.

What moves fiber PP prices, and how it ships

Fiber-grade PP is mostly homopolymer, so it follows the same monthly propylene (PGP) contract settlement and producer margin letters as other PP homopolymer. See polypropylene price per pound for how that works. Fiber grades often carry a premium over general-purpose homopolymer for tighter MFR control, controlled rheology and cleaner additive packages, and meltblown and metallocene grades sit higher again because fewer lines make them. When mask and filter demand jumped in 2020, meltblown grades ran short worldwide before most other PP did, which shows how fast a specialty grade can tighten. See gaylord vs. LTL vs. truckload for how order size changes cost. We do not post prices: every quote is for a specific grade, quantity, package and ship-to city.

We confirm a ship date with every quote. Packaged inventory ships first; a grade made on a producer’s schedule waits for its next run.

Second-sourcing a fiber grade without line breaks

• Write down what runs now. The grade, its data sheet, three to six recent COAs with lot MFR, your melt temperature profile, throughput per hole, quench and draw settings, pack life, breaks per shift, and the yarn or fabric results you track (tenacity, elongation, denier spread, basis weight, hydrohead, air permeability, filtration efficiency).
• Match on paper first. A polymer chemist compares MFR on the same test method, reactor, CR or metallocene, the distribution, the additive package (AGF, stabilizers, slip), ash and volatiles, and documents, and tells you what differs.
• Check filterability, then blend in. Run a filter or pack-pressure check, then feed the new grade as a blend, for example about 10–25% and then 50%, on one position or one line before running it alone. Stepping in catches a break-rate change before it costs a full shift.
• Watch the right signals. Pack pressure rise, breaks or drips per hour, denier and basis weight spread, die smoke and how often the spinneret needs wiping, and for meltblown, fiber diameter and charge decay.
• Get brand approvals before volume. Hygiene, medical and filtration customers often need notice and samples. Start that paperwork with the trial.
• Keep the second source warm. Buy a small regular volume and trend its COAs so it is ready if the main grade goes on allocation. See how to qualify a second resin source.

What to put on the RFQ

• Process and product. Staple, BCF, CF, tape, monofilament, spunbond or meltblown, and the end product: hygiene, medical, filter media, geotextile, carpet or sacks.
• MFR with the method. Target and range at 230°C / 446°F, 2.16 kg. For meltblown, standard die or half die (ASTM D1238 Procedure C), and whether the value is final after peroxide.
• Type and distribution. Homopolymer or random copolymer; reactor, CR or metallocene; and narrow distribution if your line needs it.
• Additive package. AGF, stabilizer level, slip for softness, and whether you add UV, electret or color masterbatch yourself.
• Cleanliness. The ash, gel and filter-test limits your line holds today.
• Documents. FDA letter, hygiene statements, and the producer’s medical-use policy if the product is medical.
• Package and volume. Bags, gaylords, bulk truck or railcar, this order and yearly use, and the ship-to city.

Common questions

If your grade is not listed, tell us what you run. We source commodity, engineering and specialty resins.