Mercerization is a continuous chemical process used for cotton and cotton/polyester goods to increase dyeability, luster and appearance. This process, which is carried out at room temperature, causes the flat, twisted ribbon-like cotton fiber to swell into a round shape and to contract in length. This causes the fiber to become more lustrous than the original fiber, increase in strength by as much as 20 percent, and increase its affinity for dyes. Mercerizing typically follows singeing and may either precede or follow bleaching (Corbman, 1975).

During mercerizing, the fabric is passed through a cold solution of 15 to 20 percent caustic soda and then stretched on a tenter frame where hot-water sprays remove most of the caustic solution (Corbman, 1975). After treatment, the caustic is removed by several washes under tension. Remaining caustic may be neutralized with a cold acid treatment followed by several more rinses to remove the acid. Wastewater from mercerizing can contain substantial amounts of high pH alkali, accounting for about 20 percent of the weight of goods.