Impurities Present in Raw Wool

The proportions of the different components of unwashed or greasy wool are:

• Moisture = 4 – 24 %
• Yolk = 12 – 22 %
• Dirt = 3 – 9 %
• Wool Fibers = 60 – 70 %

Raw wool contains three main impurities

• Wool grease
• Suint
• Dirt

These combined make up some 30-40% of the fleece weight. A typical figure of the grease content of crossbred wool is about 6%.

Wool Grease

This is a very complex mixture, consisting mostly of esters of various long-chain fatty acids with long-chain alcohols and sterols. Technically it is a wax, rather than a fat, because glycerol esters are not present. The fatty acids present fall into four main classes:

• A normal paraffin series, with even carbon numbers approximately from C10 to C26.
• An iso-acid series, with the alkyl chain terminating in a [(CH3)2-CH-] group, with even carbon numbers from C10 to C28.
• An anteiso-acid series, with a terminal isobutyl group, with odd numbers of carbons from C9 to C31.
• α-hydroxy normal and iso-acids, like [R-CH(OH)-COOH] with even carbon numbers from about C12 to C32.
• The alcohols are even more complex. There are aliphatic alcohols corresponding to the same series of structures as the acids, i.e.
• Normal alcohols from C18 to C30.
• Iso-alcohols from C18 to C26.
• Anteiso-alcohols from C17 to C27.
• 1,2-diols, i.e., [R-CH(OH)-CH2OH], both normal and iso, C16 to C24.

However, the major part of the alcohol fraction consists of sterols; the most important member is cholesterol, followed by lanosterol and dihydrolanosterol. Smaller amounts of other sterol derivatives are present. Clearly the esters formed from these acids and alcohols form a bewildering variety, especially when one considers that the hydroxy-acids and the diols can form di-esters.

Suint

Suint is the sweat of the sheep and is a complex mixture of water-soluble salts. The predominant cat-ion is potassium; the an-ions include carbonate, bicarbonate, various low molecular weight mono- and di-carboxylic acids (succinic, glycolic, glutaric etc.) and smaller amounts of long chain fatty acid anions which may originate from wool grease. Peptides and other nitrogenous substances are minor components.

Dirt

Dirt consists of all the ill-defined solid fleece contaminants. It includes mineral soil, windblown dust, vegetable matter, faecal matter (dags), skin flakes, discarded cuticle cells, and fragments of fiber broken from brittle photo-oxidized tips. In many respects, in terms of wool properties, it is the very fine mineral material, largely associated with exposed fiber tips, that is the most significant.