What Is The Manufacturing Process For Polypropylene (PP) Yarn?

Raw Material Preparation

Raw Material Selection

The primary raw material is polypropylene (PP) chips/pellets, which require high purity and a uniform molecular weight distribution. The melt flow index (MI) is adjusted based on the intended use of the yarn (e.g., the MI for PP yarn used in weaving is typically 10–30 g/10 min).

Functional masterbatches (such as anti-aging, flame-retardant, or color masterbatches) may be added to impart specific properties to the yarn.

Raw Material Drying

Polypropylene has very low hygroscopicity and usually does not require prolonged drying; however, to enhance fiber uniformity, it can be dried at 80–100°C for 2–4 hours to remove trace moisture and volatile substances.

 

Melt Spinning

PP yarn is primarily produced using the melt spinning method, which involves the following steps:

Melt Extrusion

PP chips are heated and melted in a screw extruder-with the temperature controlled between 220°C and 260°C (adjusted according to the raw material's melting point)-to form a uniform melt.

After passing through a filter screen to remove impurities, the melt enters the spinning assembly.

Spinning and Formation

Spinning speed: Typically 1,000–3,000 m/min (conventional spinning) or 3,000–6,000 m/min (high-speed spinning).

Cooling conditions: Cooling air velocity of 0.3–0.8 m/s and temperature of 20–30°C to control fiber crystallinity and orientation.

The melt is extruded through a spinneret (the number of holes is determined by the desired yarn thickness; for instance, multi-hole spinnerets are used for fine yarns) to form fine streams.

The extruded melt streams cool and solidify in the air, forming as-spun fibers (i.e., PP continuous filaments).