Morphological Change
Structural expansion of the cellulose cell wall happens when cotton fibers are treated with concentrated sodium hydroxide solutions. This mercerization swelling converts the fiber from a flat, ribbon like shape into a more cylindrical form. The lumen collapses as the internal structure fills with liquid and the polymer chains reorganize into a more accessible lattice.
This change is verified in the laboratory by measuring the increase in fiber diameter under a microscope.
Alkali Interaction
Strong caustic concentrations between 20 and 30 percent are required to initiate the reaction. During mercerization swelling, the sodium ions penetrate the crystalline regions of the cellulose, breaking hydrogen bonds and allowing the structure to expand. The temperature of the caustic bath must be controlled to ensure the reaction is uniform across the entire fabric width.
Cold mercerization typically results in more intense swelling than hot processes.
Luster Development
Light reflects more evenly from the smoothed surface of the expanded fiber. While mercerization swelling improves the physical appearance of the cloth, it also increases the surface area available for light interaction. This process creates the characteristic silk like sheen found in premium cotton apparel.
The removal of the natural twist during the swelling phase contributes to this improved reflectance.
Tensile Strength
Stretching the fibers while they are in the swollen state aligns the molecular chains along the fiber axis. Once the caustic is washed away and the mercerization swelling subsides, the reorganized structure remains significantly stronger than the original cotton. This increased durability allows for the production of finer yarns that can withstand high speed weaving.
