Mercerized
Mercerized cotton is sometimes referred to as pearl cotton or pearled cotton. It is cotton yarn or fabric that has been put through a series of processes, primarily to increase its luster. Fabric Mercerization is a chemical treatment applied to cotton fabrics to permanently impart a greater affinity for dyes and various chemical finishes. Mercerizing also gives cotton cloth increased tensile strength, greater absorptive properties, and, usually, a high degree of luster, depending on the method used. This process is carried out using caustic soda. This determines the contraction and swelling of the fibers. They become translucent and increase their tensile strength, but reduce their flexural and torsion strength. The bean-like section of the fibre becomes first elliptic and then circular, allowing a better reflection of light with a consequent increase of luster. The treatment is usually carried out under tension, with caustic soda at 28°- 30° Be(bom)’ (approx. 270- 330 g/1). If the concentration is lower than 24° Be'(bom), the treatment is called causticization and aims at enhancing the dyeing liquor penetration into the fabric.
Adding mercerizing wetting agents stable in alkaline environments ensures uniform absorption of the liquor at a temperature between 15 and 20°C. Once the operation has been carried out, alkalinity must immediately be neutralized using a diluted acid solution. From a chemical point of view, alkali cellulose is the first material to form. Hydrocellulose is the next material formed after repeatedly washing with water. This is more reactive than natural cellulose. Cotton wetting entails shrinkage of the material, which must be kept under tension, to avoid a fuzzy and woolly appearance. To ensure proper reflection of light after mercerization, fibers are singed before being subjected to the mercerizing process. This ensures the removal of fuzz and end fibres, which may otherwise inhibit the mercerizing process.