Theory of Mercerizing:
Mercerization is a process of treatment of cellulosic textiles in yarn or fabric form with a concentrated solution of caustic alkali whereby the fibers swollen, the strength and dye affinity of the materials increased, and their handle is modified. When treated in a strong solution of caustic soda, cotton fibers swell laterally and shrink longitudinally, causing interesting and important changes in the properties of the yarns or the fabrics made from them. By application of tension to the yarn in the swollen state, a permanent luster is developed; in the absence of tension, the resulting product gains in elasticity and becomes suitable for use as a stretch yarn or fabric.
Purpose of Mercerizing:
|Mercerized cotton fabric|
The main changes occurring in the alkaline treatment of cotton are:
- Solubility in solvents is increased;
- The length of yarn or area of cloth is reduced;
- Tensile strength is increased;
- Absorption of dyestuff is increased;
- Physical compactness of either cloth or yarn is increased;
- Water absorption is increased;
- Reactivity with oxygen (air) is increased;
- Reactivity of cotton at lower temperatures is increased;
- Sodium hydroxide (caustic soda) is preferentially absorbed during the process;
- Luster is increased;
- Rate of oxidation causing degradation is increased;
- Removes immature (dead) cotton;
- Lowers dye cost (up to 40 % on certain colors).
- Discontinuous or Batch method (Winch, Zigger, Jet, Pad dyeing machine)
- Semi – continuous method (Pad roll, Pad batch).
- Continuous method (Pad – steam dyeing machine).