Wool fibre
The natural qualities and properties of wool give it unique advantages when compared with other fibres. Durability, versatility and the value of spun wool is directly related to the characteristics inherent in the wool fibre.
Wool is:
- Thermal - it can store water vapour up to 35 per cent of its own dry weight yet it remains dry to touch and speeds up the body's own cooling system.
- Water resistant - it is naturally hydrophobic.
- Fire resistant - a fabric made entirely of wool is difficult to ignite, burns slowly, and has limited ability to sustain a flame.
- Durable - the interlocking protein molecules with wool fibres have the power to elongate, stretch and recover, creating an extremely robust fabric that will last for years.
- Static resistant - the retention of moisture within the fabric prevents a build-up of static electricity.
- Dirt resistant - the crimp and the scales prevent dirt from penetrating the surface of the wool fibre and the static resistance also helps to resist dust and lint from the air.
- Noise resistant - wool absorbs sound and reduces noise level considerably. Wool is also an ideal material used in such places as concert halls to attain the best acoustics possible.
- Easy to dye - the scales on the surface of the wool fibre tend to diffuse light giving less reflection and a softer colour and wool holds its colour well as the dye becomes part of the fibre.
- Comfortable - its elasticity means garments fit so well and yield to body movement, it absorbs moisture, allows your body to breathe, yet never feels damp and clammy.
- Versatile - wool fabric, knitwear and carpets are made from a wide range of wool types varying from extrafine for suits and knitwear through to broad fibres that give carpets their strength and character.
- Fashionable - wool comes in a wide choice of textures, weaves and weights, and is suitable for any style required. No fabric drapes like wool fabric. It is alive, flexible and tailors easily.
No other fabric serves so well under such a variety of conditions, nor combines so many natural properties.
Fibre Structure
The chemical structure of wool differentiates it from other fibres and affects texture, elasticity, staple and crimp formation of the wool fibres.
Wool is composed of more than 20 amino acids, which form long chains, or polymers, of protein. It also contains small amounts of fat, calcium and sodium.
Two different types of cells, the para-cortex and the ortho-cortex, develop into a three-dimensional corkscrew pattern, or helical crimp, of great elasticity. The coiled springs of wool's molecular chains contribute to the fibre's resilience. The outer cuticle and epicuticle layers of fibre give wool its ability to shed water yet readily admit water vapour.
As it grows from the sheep's skin, wool naturally groups into staples which each contain many thousands of fibres.
Important Characteristics
The most important characteristics of wool in determining its value are fibre diameter, yield, staple length, colour and staple strength.
Fibre diameter
The mean fibre diameter is the average diameter expressed in micrometres or commonly, microns.
The importance of diameter lies in the fineness of yarns, which may be spun.
Mean fibre diameter is the single most important wool characteristic, accounting for about 75 to 80 per cent of the value of the top.
Most of the fibre diameter variability encountered in wool arises because of differences within single fleeces.
Staple length, staple strength and position of break
These characteristics may be used to predict processing and product properties.
Staple length (mm) is highly correlated with mean fibre length in the top (hauteur).
The effect of staple strength is to modify expected processing behaviour and top properties of wool of a given staple length. Wool with lower staple strength will have more fibre breakage in processing and produce a top with lower hauteur. Staple strength is calculated as the force required to break per unit staple thickness, expressed as newtons per kilotex or N/tex.
The position of the break indicates where fibres are more likely o break first. Only the weakest point is noted. There is a tendency for wools with tip or base breaks to produce higher fibre losses, and for wools with middle breaks to produce tops with slightly shorter hauteur.
Yield
Yield is used to estimate the quantity of useable wool fibre present.
Vegetable matter
Vegetable matter is costly to remove and it may lead to a downgraded product if it is not removed. The level of vegetable matter is expressed as percentage vegetable matter base (vmb%), which is the amount of clean, dry vegetable matter present as a per cent of the greasy wool sample.
Crimp
The cortical structure of the wool fibre is related to crimp in fibres. Wool fibres with little crimp do not bind as well as fibres with crimp and therefore are harder for processors to spin.
Colour
Clean wool colour after scouring varies from near white through shades of cream to yellow and brown. Occasionally bacterial action will lead to unusual shades such as pink or green. It is difficult to predict scoured colour from greasy colour.
Breeding, Genetics and Nutrition
Changes in breeding, genetics and nutrition affect wool quality and ultimately the final product.
The genetic transference of wool quality characteristics is relatively high, enabling wool producers to change the quality of wool produced over time through selective breeding programs.
Wool quality characteristics are also strongly influenced by nutrition and feed supply. The effects of nutrition on wool quality are direct and can be very large and inconsistent.
Comparison with Other Fibres
Comparison of the mean fibre diameter of some available fibres shows that wool used in clothing averages between about 20 and 22 microns - all of wool's major fibre competitors are finer fibres.
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