mercerized

Mercerized refers to a treatment of cellulose fibers, most commonly cotton, with concentrated sodium hydroxide (caustic soda) under tension to produce a fiber with improved luster, strength, and dye uptake. The process was developed in the 19th century by John Mercer and remains a standard finishing step in textile production.

In the mercerization process, yarn or fabric is immersed in a caustic soda bath, typically around 20–26% NaOH. The material is held under tension during treatment to preserve its shaped form. After a set period, the fiber is removed, thoroughly washed to remove alkali, and neutralized with an acid such as acetic or sulfuric acid, followed by additional washing. Maintaining tension during treatment helps prevent shrinkage and preserves the characteristic sheen and smooth surface.

The chemical action swells the cellulose fibers and can alter their crystalline structure from cellulose I to cellulose II, increasing surface roughness and chemical reactivity. These changes enhance dye affinity, especially for anionic dyes, and often improve brightness, dye uniformity, and wet strength. Mercerized fibers generally exhibit greater dimensional stability and a smoother hand.

Mercerization is most common for cotton but can be applied to other cellulose fibers, with varying results. The process involves handling caustic solutions and generating waste that requires proper neutralization and disposal. While it adds processing cost, mercerization is valued for producing textiles with enhanced luster, dye performance, and overall appearance.