5 Must-Have Features in a melt extracted stainless steel fiber

In the past 80 years, melt-spun fibers have become a cornerstone in both the apparel and technical textiles industries, unlocking numerous innovative applications. This review aims to provide a comprehensive overview of the current state of research and development in melt-spun fibers. The technology has consistently advanced, and it is essential to outline these developments from a contemporary perspective. By delving into thermoplastic polymers, extrusion, and bicomponent technologies, this review highlights the principal markets for melt-spun fibers.

Today, chemical fibers are created by drawing a polymer melt or solution from a spinneret into a medium where it solidifies. This medium can be air, gas, water, or a coagulation bath. Drawing methods include using rollers, high-velocity air streams, or even electrostatic or centrifugal forces to produce filaments, staple fibers, and nonwovens.

Man-made fibers have a rich history. Robert Hooke conceptualized silk-like fibers in 1665, and René-Antoine Ferchault de Réaumur succeeded in producing artificial filaments in 1734. The years following saw numerous advances, including Joseph Swan's creation of filaments for light bulbs in 1883 and DuPont's launch of Nylon in 1938. Each innovation paved the way for the diverse array of fibers available today.

2. Raw Materials for Melt-Spinning

2.1. Polymers and Their Spinnability

The most commonly used materials for melt-spinning are polyamides, polyesters, and linear polyolefins. The foundational requirement for melt-spinning is that the polymer must become fusible below its degradation temperature. Thermoplastic polymers should possess several key properties to ensure processability and optimal fiber characteristics:

• Resistence to extrusion temperature and shear strain with minimal degradation and no crosslinking (thermal stability).
• High molecular weight to provide sufficient melt strength and prevent filament breakage under strain.
• Narrow molecular weight distribution to ensure consistent melt flow rheology.
• High molecular chain mobility for disentanglement and orientation under stress.
• Uniformity and purity to prevent processing fluctuations and blockages.

Processing conditions like temperature, moisture, and shear forces can significantly affect molecular weight during extrusion and spinning. Hence, precautions like drying polymers to remove moisture and volatiles are paramount. For instance, polyesters like PET, PBT, and PLA require special attention to avoid hydrolytic degradation in the presence of water.

2.2. Polyamides

Polyamides 6 and 6.6 dominate the market for melt-spun fibers. These polyamides offer outstanding wear and abrasion resistance, high tenacity, and excellent fatigue behavior. They are usually drawn to increase mechanical performance. PA 5.6, a biobased alternative to PA 6 and PA 6.6, also shows potential due to its thermal properties and high heat resistance.

2.3. Polyesters

PET remains the leading polyester for fiber production, owing to its favorable properties and ease of modification. It forms a stable, supercooled melt, and fully drawn fibers exhibit excellent performance in various applications. Other suitable polyesters include PBT and PTT, both offering superior dyeability and elasticity over PET. PEN, known for its high tensile strength and UV resistance, is also beneficial for industrial applications.

2.4. Polyolefins

Polyolefins like PP, LDPE, and HDPE are crucial for melt-spinning, especially in disposable medical and hygiene products. Polyolefin fibers are lightweight and boast a variety of applications in monofilament and multifilament spinning. Although they have limitations like poor dyeability and low resilience, innovations ensure their continued relevance in various fields.

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