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Mercerization physical andchemical changes in cotton
The document summarizes the process of mercerization of cotton, which was discovered and patented by British chemist John Mercer in the 1850s. When cotton fabric is treated with a sodium hydroxide (NaOH) solution, it causes the cotton fibers to shrink. Later developments applied tension to the fabric during NaOH treatment to reduce shrinkage. By the 1890s, the process of mercerizing cotton yarn and fabric using tension had been commercialized. Mercerization causes physical and chemical changes in cotton fibers that increase their strength, luster, and dye absorption capacity.
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Mercerization physical andchemical changes in cotton
- 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 (Unit of viscosity, approx. twice the %conc.) through cotton fabric Observation Shrinkage in the area of fabric i.e. reduction in dimensions of fabric in width and length direction.
- 2. Mercerization of cotton1850 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 cottonMain 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 tretment with concentrted 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 First German developed for mercerization of hank on commercial scale Since 1895 hank mercerization and fabric mercerization processes are used on commercial scale through out the world
- 6. Effect of NaOHconcentration 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. Untwisting of cottonfibre in NaOH solution
- 8. Effect of twist(tpi) on deconvolution count and cotton variety Deconvolution count Twist 12 20 35 45 Deconvolution 69 58 53 30 Count Cotton variety Deconvolution counts after mercerization Cotton Yarn Fibre Uppers 79 82 Texas 45 71 Zaria 28 56 Deconvolution count decreases with decrease in fibre maturirity
- 9. Effect of NaOH on cross section of cotton
- 10. Changes in crosssection of cotton on treatment with NaOH 18%
- 11. Lusture and Staplelength Cotton Staple length Lusture Lusture Unmerc Merc Mako 22 mm 25.3 70 Luisiana 18 17.8 39
- 12. Swelling in alkalinesolutions % swelling %Alkali 97 9.5 LiOH 78 18 NaOH 64 32 KOH 53 40RbOH
- 13. 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 Extent of H-bonds in intra crystlline region are 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
- 14. Increase in Tensilestrength 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.
- 15. Mercerization process Yarnmercerization Hank mercerization Warp mercerization Single thread mercerization (Liquid ammonia treatment) Fabric mercerization (Open width only) Woven fabric Knitted fabric
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- 17. Jaeggli Hank mercerizationmachine
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- 19. Fabric mercerization Padding Mangle
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