mercerizing

Mercerizing is a textile finishing process in which cellulose fibers, especially cotton, are treated with a caustic alkali solution to change their surface and physical properties. The treatment increases luster, improves dye uptake and colorfastness, and enhances dimensional stability and strength in many cases.

The process is named after John Mercer, who first demonstrated the effects in the 19th century and patented the method around 1844. Commercial development followed in the ensuing decades, and mercerized cotton became common for fabrics and yarns that require brighter color and better dye performance.

In typical practice, the fabric or yarn is immersed in a concentrated sodium hydroxide solution, commonly in the range of 18–26% NaOH, at ambient to moderately elevated temperatures. The fiber swells as the crystalline regions are dissolved and then reformed under tension to maintain a more regular, often rounder cross-section. After the desired swelling and tensioning, the alkali is removed by thorough washing and the material is neutralized with a dilute acid, such as sulfuric or acetic acid, to stop the reaction and prevent damage. Final rinsing and drying complete the process.

Mercerized cotton generally exhibits improved luster and a smoother hand, better dye uptake and more uniform color even with direct and reactive dyes, greater tensile strength or stiffness under tension, and reduced shrinkage. The degree of improvement depends on conditions such as alkali concentration, temperature, duration, and the extent of stretching.

Applications include textiles made from cotton and other cellulose fibers. The process can introduce handling and environmental considerations due to caustic waste, and excessive treating can damage fibers.