lecture 3 mercerization

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