How Spinning Creates Modern Man-Made Fibers
Polymer spinning is a vital process in textile manufacturing where polymer solutions transform into fibers. The textile industry uses the term spinning for two different processes: the spinning of a yarn, which incorporates staple fibers in a twisting or spinning process to help the fibers stay together so the yarn can form, a technique rooted in traditional hand-spinning practices but now fully industrialised for large-scale yarn production. This process is distinct from the spinning process used in the manufacture of man-made fibers whereby a polymer solution is melted and pushed through a spinneret to produce filament fibers, a highly controlled engineering method designed for uniformity and precision in synthetic fiber manufacturing.
Spinneret: The Heart of Synthetic Fiber Formation
The term spinneret comes from the tiny holes present on the abdomens of spiders and silkworms from which they produce their fibers for webs or cocoons, showing how modern fiber technology is inspired directly by biological systems. The spinneret used in man-made fiber production resembles a watering can rose or shower head: there are lots of tiny holes, each carefully engineered to determine filament fineness and performance.
The spinneret is usually found at the end of a metered pump that is underneath the vat of molten polymer, where precise pressure control ensures consistent filament thickness. This polymer is pushed through the holes to form the fibers. A spinneret can be monofilament (one hole) or multifilament (many holes), depending upon the fiber size required, with multifilaments commonly used in apparel due to their softness and flexibility. Generally, the holes are round, but other shapes are used, depending upon the end use of the fiber. Trilobal holes create fibers that reflect more light, pentagonal holes show less dirt, flat ribbon holes create an imitation straw weave. Other shapes include the following: oval, octagonal, bean, and star. Ultimately, the shape will affect the strength and hand of the fibers, because the cross-sectional geometry directly influences lustre, bulk, soil resistance and tactile feel.
Each fiber in the production of man-made fibers goes through a number of processes that require a variety of ingredients, including stabilizers, catalysts, and additives chosen to enhance durability and processing efficiency. After conducting the processes, the solution is pushed through the spinneret to form the fiber. This fiber is then set in one of four ways depending upon the type of fiber produced: wet, dry, melt or gel spun, which differ mainly in the type of solidification and the thermal/chemical environment involved.
Major Spinning Methods Used in Fiber Manufacturing
Wet Spinning
The polymer solution passes through a metered pump; this allows a measured amount of the solution to pass through to the spinneret, a key step in maintaining even denier across all filaments. The spinneret is submersed in a coagulating bath to neutralize the filaments and set them, often using acid or salts depending on the fiber chemistry. The filaments are then drawn, which extends the length of the fiber. This lengthening makes the fiber stronger because the atoms inside the fiber become aligned, increasing orientation and crystallinity for improved tensile strength. The filaments are then wound onto bobbins. This process is used on viscose, lyocell, some acrylics, modacrylics and elastanes, all of which cannot be melt-spun because they degrade at high temperature.
Dry Spinning
The polymer solution passes through a metered pump, ensuring accurate control over flow and viscosity. Once through the spinneret, the filaments pass through warm air, which evaporates the solvent and dries the filament, with most modern systems designed to recover and recycle the solvent to reduce waste. The filament is then drawn and wound onto bobbins. This process is used on acetate, triacetate, some acrylics and modacrylics, especially those that dissolve well in volatile organic solvents.
Melt Spinning
The polymer chips are melted in a large hopper and passed through a metered pump before reaching the spinneret, where temperature precision prevents polymer degradation and ensures stable melt flow. The filaments then pass through cold air, which solidifies the filament before it is drawn and wound onto bobbins, making melt spinning one of the fastest and most energy-efficient production methods. This process is used on polyamides, olefins and polyester, the world’s most widely used synthetic fibers.
Gel Spinning
This process is also known as dry-wet spinning because the filaments are cooled by passing through cold air first and then into a cooling liquid bath, a combination that preserves extreme molecular orientation. This is a special process used to achieve high strength or special fiber properties. The polymer starts in a partially liquid or gel state, unlike the other three processes which causes the polymer chains to be bound together at intervals in liquid crystal form, which results in very strong, inter-chain forces, making gel-spun fibers suitable for ballistic protection and heavy-duty industrial uses. The polymer chains in the fibers have a high degree of orientation, which vastly increases their tensile strength. This process is used on aramid and polyethylene, notably in high-performance materials such as Kevlar and Dyneema.
Fiber Modifications for Specific End Uses
Number of Holes in the Spinneret
- Monofilament – only one hole to produce a single strand fiber, used in fishing lines, bristles and industrial applications.
Multifilament – a number of holes in the spinneret gives many fibers to the yarn, resulting in softer, more flexible filaments ideal for clothing.
Shape of the Holes in the Spinneret
The chosen cross-sectional shape controls lustre, bulkiness, wicking behaviour and tactile comfort, making it a key design parameter in fiber engineering.
Other Functional Variants Added During Spinning
1. Conductive (Anti-Static):
A substance based on carbon is added to the polymer solution to ensure that the fibers will conduct static electricity, a common requirement in carpets, electronic textiles and cleanrooms.
2. Crimped, Spiral or Looped:
These effects can be created in a number of ways:
- Passing the extruded fiber between cogged wheels and then setting it according to the type of fiber, a traditional mechanical crimping method.
- A bi-component fiber (one made of two variants of the fiber, such as nylon 6 and nylon 12) is fed from within the vat of the polymer solution. The different variants set at different rates causing spiralling, looping or coiling, which gives bulk and elasticity without added chemicals.
- Variations of the chemical in the coagulating bath can cause latent crimping, activated later by heat or moisture.
3. Delustre:
Many of the fibers are bright and highly lustrous after extrusion, so they can be made dull or semi-dull via the addition of a chemical (such as titanium dioxide, barium sulphate, zinc oxide or zinc sulphate) to the polymer solution before extrusion, with titanium dioxide being the most widely used delustrant.
4. High-Tenacity:
Adding strength to the fiber generally imbues it with a thicker skin and a tighter alignment of the molecules within the fiber via high extension or stretch, making these fibers suitable for tire cords, ropes and industrial sewing threads.
5. Hollow Fiber:
Can be created in a number of ways:
- The addition of a chemical, such as sodium carbonate, to the coagulating bath causes a reaction within the fiber e.g. the formation of carbon dioxide inside the fiber, which makes it hollow, reducing weight and improving thermal insulation.
- The spinneret changes shape—a solid pin, needle, or tube is supported in the centre of the circular hole. An inert gas or reactive chemical is injected into the hollow core to prevent the fiber from collapsing until it is heat set or cool set, producing uniform, stable hollow filaments used in filtration and insulation.
6. Optical Whiteners:
A chemical is added to the polymer solution to add permanent whiteness to the fiber, by converting UV light into visible blue light to counteract yellowing.
7. Microfiber:
The holes in the spinneret are so fine that they produce a fiber that is less than one denier, leading to exceptional softness, high surface area, and superior cleaning performance.
Conclusion
Polymer spinning process, particularly solution spinning, is a fascinating transformation from liquid polymers to strong fibers. It involves dissolving polymers, extruding through spinnerets, coagulating to solidify, drawing to strengthen, and finishing for use. This process plays a foundational role in producing synthetic fibers essential to modern textiles.
References
[1] Ashford, B. (2016). Fibres to fabrics. AuthorHouse.
[2] Cassidy, T., & Goswami, P. (2017). Textile and clothing design technology. CRC Press.
[3] Nayak, R. (2019). Sustainable technologies for fashion and textiles. Woodhead Publishing.
[4] Nawab, Y., & Shaker, K. (2023). Textile Engineering: An Introduction. Walter de Gruyter GmbH & Co KG.
[5] Kiron, M. I. (2022, January 30). Manufacturing process of synthetic and regenerated fibers. Textile Learner. https://textilelearner.net/synthetic-and-regenerated-fibers-manufacturing/
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor to Wikipedia.
