What happens chemically when cellulose is dissolved
Short answer: Cellulose chains are held together by many weak bonds. Chemicals in the process break those bonds, so the chains can slide apart and form a liquid that is later pressed into new threads. Here is what happens, and what does not.
The bonds between the chains
Cellulose consists of long chains lying side by side, held together by hydrogen bonds. Each single bond is weak, but there are extremely many of them, and together they make cellulose solid and insoluble in water. That is why wood and cotton do not simply melt or dissolve when they get wet.
The chemistry breaks them
Treatment with a base and a sulphur-containing substance changes the surface of the chains, so they no longer bind to each other in the same way. The chains get room to slide and mix with the liquid. This step makes cellulose soluble. See bamboo dresses in the finished fabric.
The liquid is not a fibre
Once the chains are dissolved, you have a thick liquid that can be stirred, filtered and pumped. It has none of the properties of a fibre, and it can be neither knitted nor woven. Everything about it shows that it is an intermediate product, which is exactly what it should be before it is shaped.
Why the chains must be ordered again
A fibre gets its strength from chains lying roughly parallel and bonding to one another. Once they are dissolved, that order is lost. So the liquid is pressed through fine holes, and the chains can find each other again as they are drawn out into thin threads.
Afterwards they form again
In the hardening bath the additives are removed from the surface of the chains, and the chains bond to one another anew. The cellulose is chemically the same as before, but the structure is different, because the chains now lie ordered in a thread. That is why the fibre is called regenerated cellulose.
What is left over
The additives do not end up in the fibre. They stay in the bath and in the washing liquids that follow, and go into the factory's wastewater treatment. How well this is handled depends on the plant and the rules it works under, and you cannot read that from a finished garment.
Are there other methods
Yes. Lyocell dissolves the cellulose directly in a solvent that is reused in a closed loop, and so has fewer chemical steps. That route is not without trade-offs, but the principle is the same: the chains must be separated and joined again in a new form before thread can be spun.
What it means for the garment
When you hold a garment, you feel the result of how the chains are arranged in the fibre and how the yarn is spun. You do not feel the dissolving, but the structure that appears afterwards. The chemistry is a means to an even, soft fibre. See offers for women and Boody.
Care for regenerated cellulose
Fibres of regenerated cellulose are often weaker when wet and can wear if wrung out hard. So wash gently, at a low temperature, and let the piece dry flat or hanging. That way it keeps its shape and drape, and you enjoy it for longer.
Frequently asked questions
Are the chemicals still in the fibre?
No. They are washed out in the process, and finished textiles can be tested for residues. A new garment should still be washed before first use, so the last traces of production disappear.
Why are sulphur compounds used?
Because they are the known way to make cellulose soluble in this particular process. The method has been used for a long time, so its strengths and drawbacks are well understood.
Are there other methods?
Yes. Lyocell uses a solvent that is reused in a closed loop, and has fewer chemical steps than viscose. The fibre is usually a little firmer and stronger when wet.
