Determination of scouring/clean fleece yield

SCOURING OF WOOL

  • Scouring is the first process that raw wool goes through, to remove the dirt, grease, and other impurities. The scouring of wool is normally carried out with hot solution of sodium carbonate and non-ionic surfactants.
  • The scouring loss depends on the grease content of wool. Generally, fine wool fibres exhibit 50% weight loss compared to 5-10% in the case of carpet and coarse wools.
  • The grease that is removed (lanolin) from wool is considered as a valuable by-product and can be use in the manufacture of many cosmetics and pharmaceuticals. Lanolin consists of a highly complex mixture of esters, alcohols, and fatty acids.
  • The scouring wool needs large quantities of water and leads to environmental problem. Another problem related to wool scouring is fibre entanglement. These problems have renewed interest in solvent scouring using trichloroethylene.

Carbonising of Wool

  • Scouring does not always eliminate vegetable matter such as burrs and seeds. Heavily contaminated wool must go through a process known as carbonising. If burrs are not removed at this stage, they can cling to the wool fibres and not be noticed until the process is complete. The process of carbonising is the treatment of the vegetable matter with sulphuric acid and heat. The wool is steeped in the sulphuric acid solution, which causes the burrs to break up.
  • The wool is then subjected to heat, which converts the disintegrated material into carbon. The burrs are then finally removed, firstly by crushing and then shaken out of the wool by a machine rotating at high speed. Any remaining impurities are thus blown out of the fibre. Following carbonising, the wool should be rinsed and neutralised by a wet process. Such neutralisation should be carried out immediately after baking; otherwise fibre damage will occur during storage of the wool in such an acidic state.

Bleaching of Wool

  • Wool is generally bleached with an alkaline peroxide solution. However, there are some studies in literature, which shows that wool can be bleached using hydrogen peroxide in acidic condition with Prestogen W, a peroxide stabilizer from BASF containing organic acid salts, as well as a mixture of citric acid and sodium acetate. Hydrogen peroxide and peroxy compounds damage wool fibres, due to progressive oxidation of disulfide bonds ultimately forming cysteic acid.

Dyeing of Wool

  • Acid dyes, metal complex dyes, metal containing acid dyes and reactive dyes are used for dyeing wool. Wool fibre has large number reactive groups due to its heterogeneous side chain. Wool is needed to be dyed at boiling condition because of its higher glass transition temperature. Several research studies are reported in which wool is subjected to enzyme , UV light and plasma treatments in order to dye it in lower temperatures.
  • Chromium either used in metal complex dyes or used as a mordant, is present in the majority of dyed wools. The threat to chrome dyeing systems from environmental legislation appears to have been reduced by the widespread adoption of optimized dyeing methods and, in many cases, the installation of improved dye-house effluent treatment plants.
  • The major dyestuff manufacturers have responded to the concerns over chromium by promoting alternative metal-free dyes. New reactive dyes (e.g. Lanasol CE – Ciba) and optimized ranges of metal-free acid dyes (Sandolan MF – Clariant) have been developed to achieve a balance of economy and performance comparable to chrome dyes in targeted applications such as piece and hank dyeing, especially bright fashion shades.
  • Basolan AS (BASF) inhibits loss of bulk in package dyeing and damage to the dyed wool. This type of technology is finding use in a number of applications, particularly the dyeing of wool-polyester blends at temperatures up to 120˚C where the protective effect is claimed to be better than older style formaldehyde-release agents.
Last modified: Thursday, 12 April 2012, 11:42 AM