Date post: | 18-Nov-2014 |
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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
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
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
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
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
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
Effect of NaOH on cross section of cotton
Swelling in alkaline solutions
% swelling %Alkali
97 9.5 LiOH
78 18 NaOH
64 32 KOH
53 40 RbOH
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 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
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.
Mercerization process
Yarn mercerization• Hank mercerization• Warp mercerization • Single thread mercerization (Liquid ammonia treatment)
Fabric mercerization (Open width only) • Woven fabric• Knitted fabric
Hank mercerization
Jaeggli Hank mercerization machine
Warp Mercerization
Fabric mercerization
Padding Mangle
Pad chain machine
Pad chainless machine
Padless chainless machine
MERCERIZATION EFFICIENCY
• Deconvolution Count
• Change in fibre cross section
• Barium activity number