Mercerizing, as the special type of treatment, is a part of wet processing technology. Mercerizing is used for changing physical properties of cotton, following scouring and bleaching process.
Mercerizing is the process of subjecting a vegetable fiber to the action of a fairly concentrated solution of a strong base (sodium hydroxide 50-70 deg Tw and 18℃) so that can produce great swelling with resultant changes in the fiber structure, dimensions, morphology and mechanical properties.
Mechanism of mercerizing: The cell structures of cotton knitted fabrics differ from each other. Some cell structures are triangular while some are oval or hexagonal. When light falls on cell, it reflects the light as per its cell structure. Reflection may be regular, having influence on the luster of the fabric surface. The process which can get a regular reflection is called as mercerizing.
Mercerizing can increase the strength of the fiber by 20-30%. Cotton fiber becomes round when shrinking in the solution of caustic soda (NaOH). Then the lumen becomes small and the cell wall becomes greater. Strength of the fiber is also increased. The surface of the fabric become fine and light reflects on it constantly. For that, the luster of the fabrics and swelling power of the fiber increase. In general, low twisted yarn is suitable for mercerizing. Mercerized fabric is more suitable for dyeing and printing than the bleached fabric.
Effects of mercerizing: Various changes occur during mercerizing cotton knitted fabrics.
1.Shrinkage in the area of the fabric.
2.Tensile strength of the fabric increases.
3.Fabric luster also increases.
4.Hygroscopicity of the fabric increases.
5.Capability for absorbing dyes increases.
6.Preferential absorption of sodium hydroxide during the treatment.
7.Mercerizing increased action of lower temperature.
8.Possible compound formation soda cellulose.
Luster of the fabric is so vital that it decides attraction of the fabric. Luster of fabric depends on various factors.
1.Cross-section of the fiber.
2.Staple length of the fiber.
3.Wall thickness of the fiber.
4.Concentration of Sodium hydroxide.
5.Temperature of the mercerizing solution.
9.Doubling of yarn.
10.Degree of singeing.
11.Application of tension.
12.Rate of drying.
The luster and strength of the fabrics can be increased through mercerizing process. in generally, mercerizing is used for cotton knitted fabrics and should meet the requirements of customers. The price of mercerized fabric is higher than bleached fabric.