Melt spinning
Also searched as: melt extrusion, melt-spun, spinneret, POY, partially oriented yarn, FDY, draw ratio, drawing
Melt spinning makes synthetic filaments by melting a thermoplastic polymer, extruding it through a spinneret, cooling the jets into solid filaments and drawing them to align the molecules.
In detail
Polymer chips or a continuous melt pass through an extruder and a metering pump, are filtered, and are forced through a spinneret plate with many fine holes. The emerging jets are quenched by cross-flowing air, solidify within a short distance, and are wound up or sent straight to drawing rolls. Because no solvent is needed, the route suits polymers that melt without decomposing, including polyester, nylon and polypropylene. Hole shape sets the cross-section (round, trilobal, hollow), and combining two melt streams in one hole produces bicomponent fibers.
The science and numbers
Flow through the spinneret capillary is a shear flow that partly orients the chains; on exit, stored elastic energy relaxes and the jet swells (die swell) before being drawn down. Orientation and crystallization then develop along the spinline as the filament cools under tension. Mechanical drawing, from about two times upward, is defined by the draw ratio, the fiber speed after drawing divided by the speed after extrusion; it aligns chains along the fiber axis, raising tenacity and modulus and reducing elongation. Winding at high speed gives partially oriented yarn directly. Semicrystalline polymers such as polyamides and polyesters need this oriented structure to reach useful tenacity.
A practical example
Two polyester yarns come from the same polymer. One is wound slowly and drawn afterward to several times its length; the other is wound at high speed as partially oriented yarn for later draw-texturing. In a lab tensile test, the undrawn sample stretches easily and breaks at low load, while the drawn one is strong with little extension: processing, not chemistry, created much of the difference.
What to distinguish
Melt spinning cannot be used for cellulose, acrylic or para-aramid, which degrade before they melt; those need solution spinning. The spinneret hole diameter does not equal the final filament size, because the jet is thinned by draw-down and later drawing. 'Melt-spun' also says nothing about recycled content, dyeing method or fabric performance.
Origins and history
Melt spinning became an industrial fiber route with the synthetic polymers of the mid-twentieth century, beginning with nylon at DuPont, where Wallace Carothers' research group developed polyamides that could be drawn into strong fibers. The spinneret itself was older, having already been used to extrude solutions in early artificial silk production. Polyester and polypropylene fibers later followed the same basic melt route.
Related terms
Sources & further reading
- ScienceDirect Topics: Melt spinning
- Polymers (PMC): Melt-spun fibers for textile applications
- US EPA AP-42 Section 6.9: Synthetic fibers
- Polymer (ScienceDirect): Orientation and structure development in melt-spun nylon-6 fibres
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.