GENERAL - The most frequent cause of damage to wool is contact with moisture (fresh or salt water). It has been ascertained that in a humidity of 95 hygrometric degrees, wool will charge itself up to 25% to 30%. Wool has a high tendency to absorb moisture, which varies with its different physical states. With washed wool 17% is taken as a basis, carded wool 18% to 25% and wool not thoroughly washed 18%.
The tendency of wool to absorb atmospheric humidity provokes an increase in the temperature of a mass of fiber due to the transition of the moisture from its gaseous form to a liquid state. Wool when packed must not be excessively compressed in the bale for, in consequence of the hygroscopic property of the fiber, a considerable rise of temperature in the interior of the mass may take place, causing the fiber to deteriorate and enervate. It is known that water even when cold makes the wool fiber turgid, provoking an enlargement of the diameter of the transversal section, which increase may reach 16%. Excessive humidity affects the external stratum of the fiber, destroying it rapidly, causing it to take a yellowish shade, and lowering its resistance to strain.
Greasy raw wool in its original state and fibers which have not been de-fatted are liable to be affected by microphytes at a lower humidity degree than that at which they have appeared on washed wool. This is because of the hair of dirty wool being covered with fatty substances and with nitrogenic secretions which in a humid state constitute a good nourishing substratum for the life of both molds and bacteria. These bacteria first destroy the superficial cells of the fiber and then penetrate the wall of the surface cells and finally disintegrate the cohesive texture. Wool affected by bacteria presents a higher affinity for acid and direct coloring matter, which it absorbs in a non-uniform manner. It gets more rapidly wet than a sound fiber and suffers a higher loss of weight when subjected to washing, dyeing and bleaching.
Bacteria causing discoloration and deterioration are likely to develop when the wool is wet and exposed to air, as on the sheep's back in rainy weather, or during an interval between wet processing.
So far as is known there is no chemical treatment as protection against bacteria and mold which does not result in discoloration of the wool. As to the action of chloride of sodium on wool, it is known that, where there has been contact with salt as a result of damping with seawater, subsequent immersion in a water solution will provoke a greater swelling of the fiber than in the case of rain water damage.
In the event of moisture in the bales and in the coverings having been ascertained, an analysis of samples and wrappings will determine whether the moisture and stains evident in the same parts of the covering have been caused by rain water or by salt water. Research into the existence of marine salts must not be carried out by processing the liquid that results from washing the coverings and the wool by aid of distilled water, but by analyzing the preparation obtained by previously reducing the fiber and coverings to ashes in a refractory receptacle.
Wools, after contamination by salt water, must be opened up and washed or scoured with fresh water. Unless this is done, the wool will never dry out properly and is always liable to collect moisture from the air. Wool which has been wetted by fresh water should also be opened up for drying. All wool, more especially greasy wool, remaining in bales in a wet condition will heat in a few days and become moldy and discolored (brown stained tips of staples). This discoloration, if bad, cannot be eradicated. In all cases of water damage, speed in treatment is essential.
All burned or charred wools should be warm water washed and dried only, not scoured with hot water and harsh soaps.
In respect of changes in the fiber caused by self-heating or by various fermentative agents latent at the time of examination of the consignment, besides particular attention as to the colors and resistance of the fiber, it will be necessary to find, by chemical research, the components responsible for the degeneration of the keratin, and a careful examination of the fiber under a microscope will reveal the condition of the scales and of the walls of the cortical cells and connecting texture.
Some variation of weight arises in shipments of wool due to a natural drying out during transit.
Wool (sheep's wool), a protein fiber, is the highest value textile fiber. The value of raw wool, or more precisely greasy wool, is assessed on the basis of its content of 5 main constituents, e.g. Merino wool contains:
- 49% fibers
- 19% wool grease (lanolin)
- 6% suint
- 16% dirt (sand, dust, excrement, plant particles)
- 10% water
The main factor in determining the value of a fleece is its pure wool content. Depending on cleanness, a distinction is drawn between the following types:
- greasy wool, unscoured wool
- scoured wool
- snow white wool
Grease or unwashed wool or wool in the suint is the unscoured raw wool with a fiber content of only around 50%, in contrast to scoured wool.
Wool fibers consist of a cellular structure of keratin covered with scales. A schematic cross-section through a wool fiber reveals the following structure:
The scale layer consisting of keratinized protein cells protects the inside of the fiber and is one of the factors responsible for wool's felting property and thus for its good warmth retention properties. The fine, resilient intermediate membrane (basal membrane) allows both dyes and moisture to penetrate into the wool fiber. The cortical cell layer (cortex) forms the body of the fiber. It influences important characteristics such as strength, stretch, elasticity and crimp. The medulla is responsible for feeding the wool fiber and does not contribute in any way to its strength.
Wool is classified by:
- breed and wool quality
- recovery method
- body part and fineness
- hair type
- gender and age
- production purpose
See also IMDG Code & US CFR.
- Commodity Name: