Mercerization
Also searched as: mercerisation, mercerized cotton, mercerised, caustic treatment, perle cotton, pearl cotton
Mercerization treats cotton or other cellulose with concentrated sodium hydroxide, usually under tension, swelling the fibers so they become rounder, more lustrous, stronger and more receptive to dye.
In detail
When cotton meets strong caustic soda, the fibers swell and untwist, and their collapsed, kidney-bean cross-section becomes nearly circular. If the yarn or fabric is held at length or stretched while the alkali is washed out, the swollen form is set in a smooth, rounded shape that reflects light more evenly and gives a silky luster. Without tension the material shrinks strongly and gains dye affinity and strength but little luster, a variant called slack mercerization. The alkali is then rinsed out and neutralized.
The science and numbers
Conventional mercerizing uses roughly 20 to 26 percent sodium hydroxide by mass, traditionally cold (about 0 to 5 C), while hot mercerizing gives better penetration and more even treatment. The alkali penetrates crystalline regions and converts native cellulose I into cellulose II, the stable form after drying, with more accessible hydroxyl groups. Reported benefits include luster, higher tensile strength, greater moisture absorbency, better color yield and higher chemical reactivity. The degree of mercerization is commonly assessed with the barium activity number, which compares the barium hydroxide uptake of treated cotton with that of untreated cotton; higher values indicate more complete treatment.
A practical example
A thread maker processes two lots of the same combed cotton yarn. The lot mercerized under tension comes out visibly brighter and smoother and dyes to a deeper shade in the same dyebath; the untreated lot looks matte and lighter. To match shades, the mill can use less dye on the mercerized lot, one practical reason to mercerize before dyeing.
What to distinguish
Mercerized is a process claim, not a fiber content claim, and does not imply silk or a synthetic blend. Luster also depends on preparation: mercerized yarns are usually combed and often singed, so appearance reflects more than the caustic step. The process uses concentrated alkali and much wash water, so it is not low-impact by default. The change in crystal form is permanent and does not wash out.
Origins and history
John Mercer, a chemist and calico printer of Great Harwood, Lancashire, observed the effect of caustic soda on cotton in 1844 and patented the treatment in 1850, valuing the added strength and dye affinity despite heavy shrinkage. Luster came later: Horace A. Lowe patented treatment under tension in 1889, with a further patent in 1890, but let his patents lapse. Commercial interest grew after Thomas and Prevost patented a similar process in 1895.
Related terms
Sources & further reading
- ScienceDirect Topics: Mercerisation
- Wikisource: 1911 Encyclopaedia Britannica, Mercerizing
- Nature: Mercerising
- ScienceDirect Topics: Mercerization (chemistry)
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.