Fibre description of wool

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WOOL

Wool is animal hair from the body of sheep (usually). This hair is normally sheared once, or sometimes twice a year and its quality and quantity varies widely, depending on the breed of sheep and its environment. Wool is a member of a group of proteins known as keratin, also found in horns, nails, etc.

In addition to wool fibre, raw wool contains:

  • Natural impurities
  • Wool grease………………………………. 2-25% of greasy wool weight
  • Suint (dried perspiration) ………………….2-12% of greasy wool weight
  • Dirt ………………………………………...5-45% of greasy wool weight
  • Residues of insecticides, acaricides or insect growth regulators used as veterinary medicines to protect sheep from ectoparasites, such as lice, mites, blowfly, etc.

The percentage of the above-mentioned components may vary widely depending on the origin of wool. For example, fine wool from merino sheep, used mainly in apparel, typically contains 13% wool grease, whereas coarser wool of the types used for carpets contains an average of about 5% grease.

The clean fibre content of raw wool usually lies within the 60 to 80% range, but may vary from 40 to 90%.

Wool grease is insoluble in water, but soluble in non-polar solvents such as dichloromethane or hexane. Refined wool grease is a valuable by-product.

Suint is a water-soluble material arising from the secretion of the sweat glands in the skin. Suint is soluble in polar solvent such as water and alcohol.

Dirt can include a variety of materials such as mineral dirt, sands, clay, dust and organic materials.

Ectoparasiticides have important implications for the discharge of raw wool scouring effluent and disposal of the sludge generated by the treatment of the effluent. The chemicals known to be present in raw wool include:

  • Organochlorine insecticides (OCs)
  • γ-Hexachlorocyclohexane (lindane)
  • Dieldrin
  • DDT


  • Organophosphorous insecticides (Ops)
  • Diazinon
  • Propetamphos
  • Chlorfenvinphos
  • Chlorpyriphos
  • Dichlorfenthion


  • Synthetic pyrethroids insecticides (SPs)
  • Cypermethrin
  • Deltamethrin
  • Fenvalerate
  • Flumethrin
  • Cyhalothrin


  • Insect growth regulators (IGRs)
  • Cyromazine
  • Dicyclanil
  • Diflubenzuron
  • Triflumuron

The organochlorines are hazardous due to their persistence and bioaccumulability. They are thus likely to have long-range effects (in terms of both distance from the source and time after release). γ-Hexachlorocyclohexane (also called lindane) is the most toxic (and also the most active as pesticide) of the hexachlorocyclohexane isomers (α- and β-HCH, the β-isomer being the mot persistent. Lindane and DDT compounds are well-studied substances with demonstrated endocrine disrupting capacity.

The synthetic pyrethroid insecticides show high aquatic toxicity (predicted no-effect concentration for cypermethrin is estimated at 0,001 μg/l – UK environmental quality standards expressed as annual average). Organophosphates have lower aquatic toxicity than synthetic pyrethroids and are less persistent than organochlorines. Nevertheless they have high human toxicity (problems may therefore arise for example, for dyers with steam volatile Ops) [279, L. Bettens, 2001].

All major grower countries have banned the use of organochlorine pesticides for sheep treatment, but there is evidence that wool from some former Soviet Union States and South America contain lindane at detectable concentrations. This would suggest that either their grazing is heavily contaminated or that this compound continues to be used occasionally for sheep treatment against ectoparasites.

Wool from the majority of grower nations contains residual sheep treatment medicines which are used legally to control infestations of lice, ticks and mites. These materials may be organophosphates, typically diazinon, propetamphos and trans-chlorfenvinphos, synthetic pyrethroids, typically cypermethrin and insect growth regulators such as cyromazine. The incidence of these materials on wool id variable and depends on the permitted legal use pattern in each country.

Manufacturers can use a database containing quantitative information on the OC, OP and SP content of wool from major producing countries. ENco maintains one such database. Manufacturers use these data to avoid processing wool from suspect sources. The system is of immediate benefit to manufacturers who purchase and process wool from known sources. Commission processors of either loose fibre or yarn may be not aware of the origin of the fibre they are processing and so find it more difficult to control their raw material inputs using this approach.


Literature: BAT for the Textile Industry, July 2003


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