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Preparatory processes for wool

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Preparatory processes for wool

  1. 1. PREPARATORY PROCESSES FOR WOOL R.B.CHAVAN Department of Textile Technology Indian Institute of Technology Hauz-Khas, New Delhi 110016
  2. 2. COMPOSITION OF RAW WOOL <ul><li>Natural protein fibre obtained from hairs of sheep </li></ul><ul><li>Wool protein known as Keratin. Differs from silk protein </li></ul><ul><li>Presence of sulphur in the form of cystine amino acid containing sulphur (-CH2S-SCH2-) cystine linkage. </li></ul><ul><li>Impurities 30-70% depending on species of sheep. </li></ul>
  3. 3. COMPOSITION OF RAW WOOL <ul><li> % </li></ul><ul><li>Keratine 33 </li></ul><ul><li>Dirt 26 </li></ul><ul><li>Suint 28 (Dried perspiration) </li></ul><ul><li>Fat 12 </li></ul><ul><li>Burrs 2-10 (Dried vegetable matter) </li></ul><ul><li>Mineral matter 1 </li></ul><ul><li>Colouring matter 0.5-1 </li></ul>
  4. 4. COMPOSITION OF RAW WOOL <ul><li>Suint </li></ul><ul><li>Dried persiration. Soluble in water. Removed by washing </li></ul><ul><li>Wool Fat or Wool wax </li></ul><ul><li>Complex mixture of esters, diesters and hydroxyesters fatty alcohol like lanoline and fatty acids </li></ul><ul><li>Wool fat is yellowish in colour. Soluble in organic solvents like trichloroethylene or perchloroethylene. </li></ul><ul><li>Can be easily hydrolyzed in presence of mild alkali like ammonia at moderate temperature. </li></ul><ul><li>Wool wax can be isolated and used in preparation of good quality soap and cosmetics. </li></ul>
  5. 5. COMPOSITION OF RAW WOOL <ul><li>Dirt </li></ul><ul><li>It is held by adhesive action of suint and wool fat. Removed during scouring and washing operation. </li></ul><ul><li>Burrs </li></ul><ul><li>Vegetable fragments consisting of dried grass, straw, sticks etc. </li></ul><ul><li>Collected on the body of sheep during grazing and scraching the body against bush or tree to relieve itching. </li></ul>
  6. 6. WOOL CARBONIZATION <ul><li>Wool is resistant to acids </li></ul><ul><li>Burrs being vegetable matter not resistant to acid. </li></ul><ul><li>This property used for the removal of burr. </li></ul><ul><li>Treatment of wool with 5-7% sulphuric acid for 2 hours. </li></ul><ul><li>Hydro extract </li></ul><ul><li>Dry at 80-90 deg. C for 20-30 min. </li></ul><ul><li>Hydrolysis and carbonization of burr takes place </li></ul><ul><li>Carbonized burr removed by washing with maechanical agitation. </li></ul><ul><li>Process known as carbonization. </li></ul>
  7. 7. WOOL SCOURING <ul><li>Scouring of wool differs fromm cotton scouring </li></ul><ul><li>Wax contaent of wool is higher than that of cotton </li></ul><ul><li>Cotton can withstand strong alkaline conditions at high temperature. Wool is sensitive to alkali. </li></ul><ul><li>Sodium hydroxide is never used for wool scouring. </li></ul><ul><li>Wool wax can be hydrolyzed by mild alkali like sodium carbonate or ammonia. </li></ul>
  8. 8. WOOL SCOURING <ul><li>Emulsion scouring </li></ul><ul><li>Raw wool scoured in tanks filled with detergent or oleate soap (2-4% conc. Owf) </li></ul><ul><li>pH 8-10, </li></ul><ul><li>Temp. 55-60 deg.C </li></ul><ul><li>time 30-45 min. </li></ul><ul><li>Wash with water. </li></ul>
  9. 9. WOOL SCOURING <ul><li>Solvent scouring </li></ul><ul><li>Widely used </li></ul><ul><li>Ready solubility of wool wax in solvents like Trichloroethylene, perchloro ethylene or carbon tetrachloride. </li></ul><ul><li>No danger of wool degradation. </li></ul><ul><li>Wax can be easily recovered in pure form by solvent evaporation during solvent recovery. </li></ul><ul><li>Solvent recovery is essential for economic benefits. </li></ul>
  10. 10. WOOL SCOURING <ul><li>Freezing </li></ul><ul><li>Raw wool is subjected to low temperature of -30deg.C </li></ul><ul><li>Wool wax becomes hard </li></ul><ul><li>Crushed mechanically at low temperature </li></ul><ul><li>Remvoved by mechanical shaking of wool on a sieve. </li></ul><ul><li>All operations to be carried out at low temperature </li></ul>
  11. 11. WOOL BLEACHING <ul><li>Colouring matter </li></ul><ul><li>Melanin Present in dark colour wool (Black, Brown) </li></ul><ul><li>Phenomelanin present in light coloured wool (Cream) </li></ul><ul><li>A large proportion of wool fabric is finished in natural colours or dyed without bleaching </li></ul><ul><li>Bleaching is required for pale shade dyeings. </li></ul><ul><li>Bleaching is carried out either in yarn or fabric form </li></ul><ul><li>Two methods </li></ul><ul><li>Reductive bleaching </li></ul><ul><li>Oxidative bleaching with hydrogen peroxide. </li></ul>
  12. 12. REDUCTIVE BLEACHING <ul><li>Sodium hydrosulphite or sodium sulphoxylate formaldehyde are commonly used. </li></ul><ul><li>Sodium hydrosulphite 5-10 g/l </li></ul><ul><li>Sodium pyrophosphate 3-4 g/l (Buffer) </li></ul><ul><li>pH neutral </li></ul><ul><li>Temp. 55-60 deg.C </li></ul><ul><li>Time 1-2 hours </li></ul><ul><li>Wash with warm and cold water. </li></ul>
  13. 13. H2O2 BLEACHING <ul><li>Hydrogen peroxide 2-3 g/l </li></ul><ul><li>Stabilizer 1-2 g/l (Sodium silicate) </li></ul><ul><li>Ammonia 1-2 g/l </li></ul><ul><li>pH 8-9 </li></ul><ul><li>Temperature 60 deg.C </li></ul><ul><li>Time 1-2 hours </li></ul><ul><li>Wash with hot and cold water </li></ul><ul><li>NaOCl or NaClO2 are not used because of fibre yellowing or changing colour. </li></ul>
  14. 14. OXIDATIVE AND REDUCTIVE BLEACHING <ul><li>For extra whiteness such as for knitted yarns </li></ul><ul><li>H2O2 bleaching followed by Sodium hydrosulphite bleaching followed by optical brightening treatments are carried out. </li></ul>

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