Lecture 3 mercerization


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Lecture 3 mercerization

  1. 1. Mercerization of cotton <ul><li>John Mercer 1791-1866 British Chemist </li></ul><ul><li>Expts on measurement of viscosity of solutions of different concentrations. </li></ul><ul><li>Tried to filter the solution of NaOH 45-55 deg. TW through cotton fabric </li></ul><ul><li>Observation </li></ul><ul><li>Shrinkage in the area of fabric </li></ul>
  2. 2. Mercerization of cotton <ul><li>1850 patented process under the name Mercerization </li></ul><ul><li>Claims </li></ul><ul><li>Shrinkage in the area of cloth </li></ul><ul><li>Increase in strength </li></ul><ul><li>Increase in hygroscopicity </li></ul><ul><li>Increased capacity for dye absorption </li></ul><ul><li>Preferential absorption of NaOH </li></ul><ul><li>Increased action at lower temperature </li></ul><ul><li>Possible soda cellulose formation </li></ul><ul><li>These basic claims are valid even today </li></ul>
  3. 3. Mercerization of cotton <ul><li>Main drawback: Fabric shrinkage </li></ul><ul><li>Commercial loss: </li></ul><ul><li>Decrease in length and width of fabrics </li></ul><ul><li>No body showed commercial interest </li></ul><ul><li>Process did not become commercial till the death of Mercer in 1866 </li></ul>
  4. 4. Horace Lowe <ul><li>Horace Lowe 1869-1930 British chemist </li></ul><ul><li>Read the patent of Mercer 1889 </li></ul><ul><li>Started working to remove the problem of shrinkage on treatment with concentrated NaOH solutions </li></ul><ul><li>Thought of applying tension during NaOH treatment </li></ul><ul><li>Not only reduced shrinkage the fabric acquired lustre </li></ul><ul><li>Patented the process in 1890 </li></ul>
  5. 5. Thomas and Prevost <ul><li>1895 two German patents </li></ul><ul><li>Application of tension during NaOH treatment and during washing to remove NaOH </li></ul><ul><li>The process was commercialized in 1895 </li></ul><ul><li>Initial experiments on fabric </li></ul><ul><li>Later process developed for yarn mercerization in hank form </li></ul><ul><li>Since 1895 hank mercerization and fabric mercerization processes are used on commercial scale through out the world </li></ul>
  6. 6. Effect of NaOH concentration <ul><li>Behaviour of cotton fibre (Microscopic study) </li></ul><ul><li>Upto 15deg. Tw NaOH No change </li></ul><ul><li>16-18 deg. Tw Incomplete untwisting </li></ul><ul><li>26 deg.Tw Rapid untwisting </li></ul><ul><li>35 deg. Tw Un twisting followed by swelling </li></ul><ul><li>40 deg Tw and above Untwisting and swelling together </li></ul>
  7. 7. Effect of NaOH on cross section of cotton
  8. 8. Swelling in alkaline solutions <ul><li>% swelling %Alkali </li></ul><ul><li>97 9.5 LiOH </li></ul><ul><li>78 18 NaOH </li></ul><ul><li>64 32 KOH </li></ul><ul><li>53 40 RbOH </li></ul>
  9. 9. Mercerization Physical changes in cotton <ul><li>Effect of strong caustic soda </li></ul><ul><li>Fibre swelling </li></ul><ul><li>Breaking of old bonds </li></ul><ul><li>Opening of fibre structure </li></ul><ul><li>Swelling not only in amorphous region but in the intra crystalline region i.e. surface of crystalline region </li></ul><ul><li>On removal of caustic soda by washing </li></ul><ul><li>New bonds are formed </li></ul>
  10. 10. <ul><li>Extent of H-bonds in intra crystlline region is not to the same extent compared to unmercerized cotton </li></ul><ul><li>Increase in amorphos content </li></ul><ul><li>Increase in number of OH groups </li></ul><ul><li>Both these factors responsible for higher moisture content, increased dye uptake and increased reactivity </li></ul><ul><li>Amorphous content is more in slack mercerization compared to tension mercerization </li></ul>
  11. 11. Increase in Tensile strength <ul><li>Removal of convolutions removes the weak spots at the point of reversal. </li></ul><ul><li>Alignment of fibres in the new configuration after treatment with caustic soda </li></ul><ul><li>More parallel and compact due to removal of convolutions </li></ul><ul><li>Penalization and compactness is much better on application of tension. </li></ul><ul><li>Improvement in strength is much higher in case of tension mercerization compared to slack mercerization. </li></ul>
  12. 12. Mercerization process <ul><li>Yarn mercerization </li></ul><ul><li>Hank mercerization </li></ul><ul><li>Warp mercerization </li></ul><ul><li>Single thread mercerization (Liquid ammonia treatment) </li></ul><ul><li>Fabric mercerization (Open width only) </li></ul><ul><li>Woven fabric </li></ul><ul><li>Knitted fabric </li></ul>
  13. 13. Hank mercerization
  14. 14. Jaeggli Hank mercerization machine
  15. 15. Warp Mercerization
  16. 16. Fabric mercerization Padding Mangle
  17. 17. Pad chain machine
  18. 18. Pad chainless machine
  19. 19. Padless chainless machine
  20. 20. MERCERIZATION EFFICIENCY <ul><li>Deconvolution Count </li></ul><ul><li>Change in fibre cross section </li></ul><ul><li>Barium activity number </li></ul>