Alkaline Treatment
Highly concentrated sodium hydroxide solutions are used in the textile industry to modify the physical structure of cotton fibres. This chemically active liquid, commonly called mercerizing lye, typically holds a concentration of twenty to thirty percent by weight. Its application alters the internal structure of the cellulose, which improves the lustre and strength of the fabric.
Swelling Action
The primary function of mercerizing lye is to break the internal hydrogen bonds within the cotton cellulose. As the concentrated sodium hydroxide penetrates the cotton fibres, it causes them to swell radially while shrinking longitudinally. To prevent the fabric from shrinking and to orient the swollen molecules, the textile is held under high tension during the treatment.
This tension is essential for developing the characteristic high lustre and silk-like appearance that premium apparel brands require.
Recycling Process
Industrial mills use recovery systems to reclaim and concentrate the used mercerizing lye that is washed out of the fabric. The dilute wash water is collected and passed through multi-stage evaporators to restore the sodium hydroxide concentration to the required processing level. This recycling loop reduces the consumption of fresh chemicals and minimizes the volume of alkaline wastewater that must be neutralized before discharge.
It represents a significant cost saving and a critical environmental control point for the textile mill, as it allows up to ninety percent of the sodium hydroxide to be reused in subsequent treatment cycles, significantly lowering the overall chemical footprint of the production facility.
Quality Assessment
Continuous monitoring of the density and temperature of the mercerizing lye is necessary to ensure consistent treatment quality. If the lye concentration drops below the critical threshold, the mercerization will be incomplete, resulting in patchy dye uptake and reduced strength. Modern mills use automated inline refractometers or density meters to adjust the chemical feed in real time.
This ensures that every meter of fabric receives the same level of treatment, preventing shade variation in the final garments.
