mercerisation

Mercerisation, or mercerization, is a textile finishing process applied primarily to cotton and other cellulose fibers. It involves treating the fibers with a concentrated sodium hydroxide solution under mechanical tension. Named after John Mercer, who first reported the process in 1844, mercerisation increases luster, strength, and dye uptake.

The process typically uses 18–25% NaOH, sometimes up to about 28%. The fabric or yarn is padded or immersed in the alkali while held under tension to preserve a round cross-section as the fiber swells. Temperatures range from ambient to around 60°C, with hot mercerization at the higher end. After alkali treatment, the fibers are neutralized with a dilute acid, then thoroughly washed and dried under tension to maintain shape.

Chemical and physical changes accompany mercerisation. The alkali causes the cellulose to swell and induces a change from crystalline cellulose I to cellulose II, producing a more amorphous, reactive structure. These changes result in greater luster, improved dye uptake and color fastness, and higher wet strength and dimensional stability.

Variants and considerations include cold (room-temperature) mercerization, which is gentler, and hot mercerization, which can yield higher luster. Semi- or partial mercerization is also practiced. While most common on cotton, the method can be applied to other cellulose fibers. Proper rinsing and neutralization are essential to remove caustic and to minimize environmental impact.

Safety and environmental impact: Mercerization uses caustic soda and generates alkaline effluent, requiring appropriate handling, wastewater treatment, and waste management.