What changes mercerising bring on cotton? 

• Improved luster
• Increased ability to absorb dye
• Improved reactions with a variety of chemicals
• Improved stability of form
• Improved strength/elongation
• Improved smoothness
• Improved hand

Reaction of Cotton with alkaline solution:

     If cotton is dipped into a strong alkaline solution such as lithium hydroxide, caustic soda, or potassium hydroxide, the fibers will swell and shrink. One can get following  two effects:

•       Under Tension: Yarn/Fabric are placed under tension while in this swollen state and then rinsed with water, the alkali will be removed and a permanent silk-like luster will result.
•        Without Tension:  Alternatively, after swelling, if the alkali is rinsed off when the fiber is in its shrunk state, an increase in luster may not be obtained, but the fibers will fix in that shrunk state, thus giving good elasticity to external stress.  

       Behaviour of Cotton fibre with different concentration of Sodium hydroxide: If a cotton hair is dipped in different alkaline solutions, no change in appearance will be visible up to 10°Bé (6.58%), but above 11°Bé (7.3%), the hair slowly loses its natural twist (this usually being in the order of 150-300 times per inch). 

       Above 13°Bé, untwisting and shrinkage in the longitudinal direction now gradually starts to increase, and as the concentration nears 16°Bé, untwisting and shrinkage advance rapidly. Between 18 (12.69%) and 22°Bé (16%), shrinkage of the length reaches its maximum and untwisting for the most part ceases. 

Relationship between density, Baume (Bé°) and Concentration (C%)