Changes in cross section view of cotton with strong alkali:

When cotton fibre treated with strong alkali, it swell. The cross section view of cotton fibre changes from bean type (squashed circular pipe) to oval shaped when reacted with strong alkali like sodium hydroxide  during mercerization. This change in cross section brings luster in the fibre. Following figures shows the changes occur in cross section of cotton fibre during mercerization:

The swelling which occur in the cotton fibre with strong alkali treatment is relative to the longitudinal shrinkage in the cotton fibres. It means that with the increase in swelling of the fibre, length of the fibre decreases. 

Occurring Physical Changes in cotton during mercerization:

Mercerization brings following physical changes in the cotton:

1. Swelling of fibre in the amorphous and intra crystalline regions
2. Swelling brings breaking of old bonds
3. Opening of fibre structure
4. After washing sodium hydroxide is removed and new bonds are formed
5. Increase in amorphous region and Increase in number of OH groups, due to these two factors the cotton has higher moisture content which resulted higher dye uptake and reactivity
6. Slack mercerization has more amorphous region than tension mercerization

Effect on strength of cotton by mercerization: 

Mercerization process removes convolutions which also remove weak spots at the point of reversal. The caustic treatment align fibres in the new configuration. More parallel and compact fibres due to removal of convolutions. The  more parallel and compact fibres obtain when tension is applied. Due to these changes higher strength is obtained in the mercerized fabric/yarn than unmercerized fabric/yarn. The strength is found to be more in the tension mercerization than slack merceisation. 

Types of Mercerization 

Following are the important Mercerization methods:

a) Yarn mercerization 

Batch : 

• Hank mercerization
• Cheese mercerization

Continuous : 

• Single end mercerization
• Tow mercerization
• Warp mercerization

b) Knit fabric mercerization

• Open mercerization
• Closed mercerization (Round mercerization, tubular knit mercerization)

c) Woven fabric mercerization

• Chainless mercerization (Roller mercerization)
• Chain mercerization (Stenter mercerization)
• Batch-up mercerization