Chemical Characteristics of Wool Fiber:
Whereas cotton, flax and the other plant fibers re basically cellulose, wool is protein. Keratin, the substance of wool is similar in its essential structure to the other proteins from which much of the animal body is built. The chemical structure of wool fiber differs only slightly from that of feathers, hair ad horn.
In their chemical behavior, proteins are quite different from cellulose. They are more easily degraded and attacked by chemicals, particularly of certain types. They do not, in general, have the resistance to environmental conditions that is so characteristic of cellulose.
Effect of Acids:
Wool is attacked by hot concentrated sulphuric acid and decomposes completely. It is in general resistant to other mineral acids of all strengths, even at high temperature, though nitric acid tends to cause damage by oxidization. Dilute acids are used for removing cotton from mixtures of the two fibers; sulphuric acid is used to remove vegetable matter in the carbonizing process.
Effect of Alkalis:
The chemical nature of wool keratin is such that it is particularly sensitive to alkaline substances. Wool will dissolve in caustic soda solutions that would have little effect on cotton. The scouring and processing of wool is carried out under conditions of low alkalinity. Even weakly alkaline substances such as soap or soda are used with care. Soda will tender wool and turn it yellow if used in too concentrated a solution, particularly if the solution is too hot. Ammonium carbonate, borax and sodium phosphate are mild alkalis that have a minimum effect on wool. Ammonia, carefully used, will not cause damage.
Effect of Organic Solvents:
Wool has a good resistance to dry-cleaning and other common solvents.
Wool is attacked by moth-grubs and by other insects.
Wool has a poor resistance to mildews and bacteria and it is not advisable to leave wool for too long in a damp condition.
Uses of Wool Fiber:
One of the first things we meet on entering the world is wool. And, although it is no longer compulsory by law, wool is still very often our closest companion where we leave. Woolies are worn by babies because they are warm and airy. Wool clothes are healthy and hard wearing. The have many other properties- some desirable, some not. All are in one way or another direct consequence of the properties of the fiber itself.
The wool fiber has excellent spinning characteristics. Its crimp enables the fibers to cling tenaciously together when they are spun. Because of this, it is possible to make a relatively strong yarn from wool fibers without twisting them very tightly. Knitting wool, for example, can be spun very loosely and yet is quite coherent.