Lecture 3 mercerization
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The document discusses the history and process of mercerization of cotton. It describes how John Mercer discovered in 1791 that treating cotton with a sodium hydroxide solution caused it to shrink. In the 1850s, Mercer patented the mercerization process. Later improvements by Horace Lowe and Thomas and Prevost reduced shrinkage by applying tension during treatment. The process was then commercialized in 1895 and is now widely used to increase cotton's strength, dye absorption, and other properties.
Lecture 3 mercerization
- 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
- 14. Jaeggli Hank mercerization machine
- 16. Fabric mercerization Padding Mangle
- 20. MERCERIZATION EFFICIENCY Deconvolution Count Change in fibre cross section Barium activity number