Nylon resin for fiber and monofilament: PA6 and PA66 chips by viscosity, luster and stabilizer

PA6 or PA66 for yarn, carpet and monofilament

For the molding side of this choice, see nylon 6 vs. nylon 66. In fiber the same chemistry applies: PA66 melts about 40°C / 72°F higher and holds up better to heat, and PA6 processes over a wider window and dyes deeper.

Typical choices. Grades within each family vary, so confirm on the data sheet.

Relative viscosity windows by use, and which test

Fiber and monofilament nylon is bought on solution viscosity, not melt flow, because water in the sample skews a nylon melt flow test. Three scales are common, and they do not convert one for one:

• Formic acid RV or FAV, ASTM D789. Viscosity of a concentrated nylon solution in 90% formic acid relative to the solvent, at 25°C / 77°F. Common on U.S. sheets. Medium-viscosity PA6 reads about FAV 55–61.
• Sulfuric acid RV. 1 g of nylon per 100 mL of 96% sulfuric acid, which many sheets report under ISO 307. Common on European and Asian chip sheets, with numbers like 2.4 to 4.2.
• Viscosity number (VN), ISO 307. In mL/g, often 0.5% in 96% sulfuric acid; some producers use 90% formic acid instead.

Pairs from producer sheets help you place a number: one PA6 carpet grade reads FAV 61 and sulfuric RV 2.83; one PA6 grade for monofilament and compounding reads sulfuric RV 2.62–2.83 and VN 142–158; one high-viscosity PA6 film and monofilament grade reads RV 3.89–4.17 and VN 240–260. Ask for the method with every number.

Typical published ranges from producer chip sheets and price-assessment specs, as starting points, not specifications. Compare grades on the same scale and let a chemist check any equivalent before you switch.

Bright, semi-dull and full-dull: what the TiO2 does

• Bright. No titanium dioxide (TiO2), or a trace up to about 0.03% (some producers call that level semi-bright). Highest luster. Many carpet BCF grades and most monofilament are bright.
• Semi-dull. About 0.3% TiO2. A common choice for apparel yarn: softer luster and less see-through.
• Full-dull. About 1.3–1.6% TiO2 on the producer sheets we checked; some run higher. A matte, cotton-like look and high opacity for apparel and linings.
• Side effects. TiO2 is abrasive, so dull yarn wears guides, rolls and cutters faster. Some forms of TiO2 also speed light damage to nylon, so ask about light stability for dull yarn in sunlit uses.
• Check it on the COA. TiO2 or ash content confirms the luster you bought. Bright and semi-dull chips mixed in a silo show up as luster streaks and dye differences.

Heat-stabilized and light-stabilized yarn grades

• Heat-stabilized (HS). Industrial yarn, airbag yarn, tire cord, rope and some monofilament use copper-halide stabilized PA66 or PA6, which protects strength through hot processing and hot service. Copper-halide grades can tint slightly, and some electrical customers avoid halides.
• Light-stabilized. Automotive upholstery, carpet in sunlit rooms and outdoor fabric use light stabilizers such as hindered amines, sometimes built into the polymer chain so they do not wash out. Name the light-fastness test your customer uses, such as an automotive xenon-arc exposure.
• UV for outdoor monofilament. Trimmer line, netting, outdoor brushes and rope often get a UV package or carbon black by masterbatch. Say whether you add it or need it in the chip. See masterbatch vs. precolored resin.
• Match the package, not the letters. Two grades both called HS can age very differently. Compare the stabilizer type and level, and test aged strength if the yarn runs hot. See nylon grades.

End groups and dyeability

Acid dyes, the common dyes for nylon, attach at amine (NH2) end groups, so the amine end level sets how deep a yarn dyes. Producers sell grades by dye level, such as light, medium and deep dye, with deep-dye grades carrying more amine ends. One producer’s PA66 textile grades read about 44 meq/kg. A small shift in amine ends changes the shade, which is why yarn from two chip sources can dye in visible bands (barré) even at the same viscosity.

• Terminated or unterminated. A terminated grade has some chain ends capped, so viscosity holds steadier in the melt and on high-speed lines. Unterminated grades keep reacting in the melt. Treat a switch between them as a material change.
• Acid-dye-resist and cationic-dyeable polymer. Some carpet and apparel polymers block acid-dye sites for stain resistance or cross-dye effects. These are special grades, not interchangeable with regular dye polymer.
• Put it on the RFQ. Amine end groups with a range, the producer’s dye-level name, and whether you dye the yarn, the fabric or the carpet.

Moisture as shipped and dry-to-spin

Fiber and monofilament chips ship dry in sealed moisture-barrier packaging. Producer limits for PA6 spinning, film and monofilament chips often run about 0.10–0.15% maximum on the North American and European sheets we checked. Some PA66 textile chip is packed at a higher, controlled moisture by design, so read the sheet for your grade.

Moisture matters more in spinning than in molding because it changes viscosity in the melt. At melt temperature, water and chain length move toward a balance: chips that are drier than the line was set up for can build viscosity, and wetter chips lose viscosity and can bubble. Many spinners therefore hold chip moisture to a target band rather than as low as possible. Ask what moisture your line was tuned for and hold a new source to it.

If you dry, use a dehumidifying dryer at about 80°C / 176°F, as on our drying chart. Over-drying can yellow nylon and raise melt viscosity. Close liners after every draw, since open pellets take up water within hours.

PA6 also carries extractables, mostly residual caprolactam. Sheets set a maximum, often under 1% for textile chips; one carpet grade we checked allows 1.1%. Extractables affect fumes at the spinneret and dye uptake, so put a limit on the RFQ.

Monofilament: fishing line, bristles, trimmer line and filament

Typical choices; grades vary. PA610, PA612, PA11 and PA12 cost well above PA6, so use them where low moisture uptake earns its place.

What moves fiber nylon prices, and how it ships

PA6 follows caprolactam, which follows benzene, with ammonia and natural gas in the cost. PA66 follows adipic acid and hexamethylenediamine, and so depends on the few plants that make adiponitrile. There is no monthly North American settlement for fiber chips. Large spinners buy on contracts tied to raw materials, and price services publish textile-grade nylon assessments, mostly for Asia. Imported chip competes with domestic resin, so ocean freight, exchange rates and duties move the delivered cost. Long-chain nylons (PA610, PA612, PA11, PA12) sit well above PA6 and PA66 and come from fewer producers. See how nylon prices are set and PA66 shortage alternatives. 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 yarn or monofilament grade, and what to put on the RFQ

• Polymer and end use. PA6, PA66, copolyamide or long-chain nylon, and the product: apparel yarn, BCF, industrial yarn, fishing line, trimmer line, bristles or filament.
• Viscosity with its method and range. FAV or RV by ASTM D789, sulfuric RV, or VN by ISO 307, plus the lot spread your line holds today.
• Luster and color. Bright, semi-dull or full-dull with the TiO2 level, or the color you add by masterbatch.
• Stabilizers. Heat (copper-halide or organic), light and UV.
• End groups and termination. Amine end groups and dye level, terminated or unterminated.
• Moisture and extractables. Moisture as packed, the moisture your line runs at, and the extractables limit.
• Trial the way the line runs. Compare three to six COAs first, then run a blend or one position, watching breaks, pack pressure, draw ratio, denier or diameter spread, tenacity and, for yarn, a dye test against your current chip. See how to qualify a second resin source.
• Package and volume. Bags, gaylords or octabins, 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.