Lecture 3 mercerization

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