- Wool as a textile fibre
|Last update: April 3, 2012 07:22:35 AM|
WOOL AS TEXTILE FIBRE
Assistant Director (Research)
Agricultural Research Institute, Grootfontein
THOUGH vegetable fibres were probably the first to be used for spinning and weaving into cloth, animal fibres in the form of skins and furs were undoubtedly the earliest form of clothing used by primitive man. History produces no record of when wool was first spun and woven.
The oldest evidence of wool comes from Asia Minor, where, according to historians, under a succession of ruined cities at Tell Asmar peals were found indicating an elaborate system of personal ownership of flocks of woolled sheep. The date is given as 4200 B.C. and there is evidence that wool was already being used for trading purposes.
Today, as for many years past, cotton, wool, flax and silk are the most important of our natural textile fibres.
Wool is an expensive fibre compared with cotton as it involves a second step, the animal, in its production. But wool is so different a fibre, so unique and valuable in its properties that there will always be a sustained demand for it by those who can afford it.
The supply of raw wool available to the world every year amounts to about 2 400 million kg of clean or pure wool. This crop of wool is sufficient to meet the world's needs, and the supply is augmented to some extent by re-using wool, which has already been made into yarns and fabrics, and even worn.
CLASSIFICATION OF WOOL
Broadly speaking there are three main classes of wool, namely fine wool (60s and upwards), cross- bred wool (46s – 58s) and carpet wool (28s –44s). The two former cover the apparel class.
Only the Merino breeds produce fleeces, which can be classified under this type. Merino wool is obtained from sheep exhibiting the typical characteristics of the Merino in their wool. These characteristics include length, fineness, colour, crimp, staple formation and handle.
Crossbred sheep produce wool with a fibre fineness of 46s to 58s, but this classification also includes the wool of purebred mutton-wool breeds such as the Corriedale and Romney Marsh.
Carpet wool is obtained mainly from fat-tailed and fat-rumped sheep kept in many parts of the world under primitive conditions. This type of wool, as the name indicates, is largely used in the manufacture of carpets and to a much lesser extent for the manufacture of tweed, coarse cloth, etc.
WOOL IN USE
Wool is an excellent textile fibre, not because of one or two outstanding properties, but on account of the fact that it possesses the best combination of desirable properties.
The wool fibre has excellent spinning properties. Its natural crimp and scaly surface structure enable the fibres to cling tenaciously together when they are spun. Because of this, it is possible to make a relatively strong yarn from wool fibres twisting them very tightly. Knitting wool for example, can be spun very loosely and yet it is quite coherent.
The wavy structure and resilience of the wool fibre and the looseness of the yarn are largely responsible for wool's warmth as a material. The fibre itself is a poor conductor of heat, but the real insulation is provided by the air trapped' inside the fabric. Wool's high natural crimp means that woollen yarns and fabrics tend to be lofty open structures, which hold much heat-insulating air inside them. The high elastic recovery and resilience of wool prevent the fibres from bedding down and the fabric becoming thin during wear.
Wool is an unusually resilient fibre. Its high elongation at break is combined with a high elastic recovery that gives wool unique properties in this respect. The natural crimp of the wool fibre contributes to the overall elasticity, but the property is a fundamental one which is derived from the curled, cross-linked structure of the wool molecules themselves.
The flexibility and elasticity of wool fibres contribute to the high resistance of wool fabrics to crushing and creasing. The fibres can be distorted, but they will tend to return to their normal shape again. Furthermore, wool fibres can be bent backwards and forwards tens of thousands of times without breaking. Elbows and knees of wool suiting can thus stand up to wear that would quickly reduce other materials to holes.
All fibres tend to absorb moisture when in contact with the atmosphere.
In practice, the moisture-absorbing properties of a fibre are described by a figure known as the "regain". This is the weight of moisture present in a textile material expressed as a percentage of its oven-dry weight.
Fibres vary greatly in the amount of moisture they will absorb. Wool, for example, has a regain of 16 percent, cotton of 8,5 percent and Terylene 0,4 percent. A fibre which absorbs moisture readily is often most suitable for use in certain types of clothing fabrics. These fabrics will absorb perspiration from the body and will hold considerable amounts of water.
Wool absorbs moisture to a greater extent than any other fibre and this is one of wool's most important characteristics. The moisture disappears into the fibres and there is no feeling of dampness about the garment, even though it may be holding a large quantity of water.
When wool has absorbed moisture, it will get rid of it again slowly into the surrounding air with the result that there is no sudden cooling to chill the body. Thus, the moisture absorbing properties make it a very hygienic and comfortable fibre to wear.
Synthetic fibres, which often have a very low moisture regain, are easily washed and dried by comparison with fibres which absorb a lot of moisture. On the other hand, they tend to accumulate charges of static electricity much more readily than the moisture absorbing fibres.
The felting of wool which causes the shrinkage of wool fabrics and garments is one of its greatest disadvantages. However, the felting characteristics of wool fibres is used to advantage in the production of "felts". These are simply masses of fibres held together entirely by their natural holding power without being spun or woven. Some types of woollen fabric are woven and then felted deliberately by the process known as "milling" to give them a fluffy, matted texture. Deliberate felting is used in making fabrics such as beavers, meltons, doeskins and velours.
Effect of Heat
In the presence of air, most fibres will burn. The readiness with which they catch fire and support combustion is of immense importance. Many accidents are caused every year by clothing catching fire, and there is an increasing realization of the need for reducing inflammability of textile fibres and fabrics. The fact that wool does not support combustion makes it a very safe fibre for use where there is a possibility of fire.
The challenge facing wool as a textile fibre is to compete with man-made fibre as a modern textile fibre. Wool is the most outstanding textile fibre, but at the same time we must admit that wool also has certain shortcomings.
The consumer of textiles can no longer be satisfied, with the slogan "wool is warm" and "it absorbs moisture" etc.
The attractiveness of colour, design and easy care properties must be part and parcel of the desirable properties that the consumer is looking for in a textile.
It is thus essential that research should be carried out into the shortcomings of wool.
Today there are modern and fully equipped wool textile research laboratories the world over and tremendous progress has already been made in eliminating some of the shortcomings of the wool fibre.
Karoo Agric 1 (1), 19-22