What a spinneret does
Short answer: The spinneret is a metal plate with thousands of small holes. The liquid cellulose is pressed through, and each jet becomes a thread as it hits the hardening bath. This is where the fibre's form is decided, long before it becomes yarn.
A plate with many holes
A spinneret looks most like a metal shower head, where the holes are very small and sit close together. The liquid is pressed in on one side and comes out as thin jets on the other. Each hole gives one thread, so the number of holes decides how many threads form at the same time.
The holes decide the thickness
The diameter of the hole and the speed at which the liquid is pressed through decide how thick the thread becomes. This is where the fineness of the fibre is set, before it is even solid. Small adjustments to the nozzle can therefore give a fine, soft fibre or a coarser, stronger one, depending on use.
The jet hardens in the bath
The liquid meets an acid solution that makes the cellulose come out as a solid. The thread forms in a few seconds and becomes firm enough to be drawn onward. You could say the nozzle gives the shape and the bath gives the firmness. See bestsellers for men in the finished fabric.
The threads are stretched afterwards
The newly formed threads are drawn out so the molecule chains line up and lie more in parallel. This makes the fibre stronger and less likely to break during spinning and weaving. Without the stretching, the thread would be soft and weak, and hardly usable for anything but filling.
From threads to fibres
After stretching, the threads are gathered into large bundles called tow. They are washed to remove traces of the bath and treated to give the wanted feel. Only then is the material ready to be cut or wound, depending on whether it becomes staple fibre or continuous thread.
Fixed lengths like cotton
The threads are cut to fixed lengths so they behave like staple fibres, just like cotton. That lets them be spun on the same machines and blended with other fibres in the yarn. So there is yarn of pure viscose, but also yarn where it is blended with cotton or other materials.
Continuous threads for smooth fabrics
The threads can also be left continuous. That is called filament, and it is used for smooth fabrics with a cool, silky hand. The difference is not in the chemistry but in what happens after the nozzle. The same process can give two very different materials, depending on how the threads are treated afterwards.
The nozzle is a delicate tool
The holes are so small that they can clog if the liquid is not perfectly clean. So the liquid is filtered thoroughly before the nozzle, and nozzles are cleaned and replaced regularly. It is precision work, where small deviations can give an uneven thread. See JBS of Denmark.
What you feel as a buyer
As a buyer you cannot see the nozzle, but you can feel the result. An even thread gives an even yarn and a fabric without obviously thick and thin spots. Read the content label to see which fibres are included, and see Urban Quest for examples of everyday clothing for men.
Frequently asked questions
How many holes are in a nozzle?
It varies from a few hundred to tens of thousands, depending on the plant and on which type of fibre is being made. More holes give more threads at the same time.
Why are the fibres cut into short pieces?
Because they are meant to be spun as staple fibres, like cotton. Then they can run on the same machines and be blended with other fibres when the yarn is made.
Can the fibres be made as continuous threads?
Yes. That is called filament, and it is used for smooth fabrics, among other things. Here the threads are not cut but stay as long, unbroken threads throughout the process.
