From Fleece to Grease

Centrifugation process

To speed up and improve the separation of liquid and hydrophobic wax during the first centrifugation, special acids are sometimes added to the scouring solution. These cause a chemical breakdown of the soap that holds the wax in a stable emulsion.

However, modern processing plants generally miss out this step because it releases free fatty acids in the process. This in turn leads to wool wax products with high acid values, which is undesirable.

While only 50% of the available wool grease can be recovered by the centrifugation process, this low yield is compensated by the superior quality of the obtained raw material.

 
Alternative recovery methods

As well as the standard centrifugal technique which is used by most factories, wool grease can be recovered through several alternative methods, such as solvent extraction followed by filtration and distillation.

If the grease is directly washed out of the wool by organic solvents, the yield will be generally higher and the fleece will be protected from adverse alkaline treatment.

Wool grease is a wax

Wool grease, the common term for this substance, is actually a misnomer. Chemically speaking, the greasy raw material is not a fat but a wax, because it lacks the glycerol content typical of body fat.

Wool grease is a complex mixture of esters, di-esters and hydroxy esters formed by condensation of high molecular weight lanolin alcohols with lanolin fatty acids. The overall molecular weight ranges from 790 to 880.

After saponification, scientists have identified in lanolin:

• 69 aliphatic and branched alcohols (C12-36, approx. 7% di-hydroxy alcohols)
• 6 alcohols with steroidal structure (cholesterol, lanosterol, agnosterol and their hydrated derivatives)
• approximately 160 fatty acids (C7-41, ca. 32% bi-functional hydroxy acids).

About 40% of lanolin esters are alpha-hydroxy esters (AHEs). Approximately 1% to 8% of the fatty acids and 6% to 12% of the alcohols are present in their free, unbound form.

Naturally occurring substance

Considering the almost random combinations of the 69 aliphatic alcohols, 6 sterols and the 160 lanolin acids, the estimated number of lanolin mono-ester compounds that are theoretically possible exceeds 10,000 – even if calculated by leaving out di-ester compounds.

The exact number of individual ester ingredients effectively present in the mixture is not known. Crude wool wax contains residues of:

• water
• detergent
• free fatty acids and their metal soaps
• pesticides
• environmental contaminants
• particulate insoluble matters.

Impurities

Environmental contaminants, such as ubiquitous polyaromatic hydrocarbons (PAH) that are present in most natural substances, can be removed from the crude wool wax by sophisticated refining methods.

Other impurities in wool wax are a result of veterinary procedures necessary for the health of the sheep. After the animals are shorn, they are treated with agents to protect them against pests.

Only water soluble and biodegradable organophosphorous compounds are allowed for this purpose. Using persistent pesticides (such as organochlorine preparations) is illegal in all leading sheep wool production countries. In this respect, New Zealand and Australia are leaders in ecologically responsible sheep farming.

State-of-the-art engineering makes it possible for modern refineries to remove traces of contaminants, residues and other impurities almost beyond the detectable limit.