Scouring Chemistry
Chemical pre-treatment of linen yarn uses concentrated sodium hydroxide to remove non-cellulosic impurities such as pectin and hemicellulose. An unresolved presence of hard water ions or residual sizing agents creates caustic scouring interference, which disrupts the uniform solubility of these impurities. High concentrations of calcium or magnesium in the process bath react with the dissolved fatty acids to form insoluble soaps.
These deposits settle on the yarn surface and prevent uniform dye absorption during subsequent finishing. The action of the scouring liquor requires strict monitoring of both water hardness and surfactant concentrations.
Cellulose Degradation
Alkaline solutions at high temperatures risk weakening the flax fibers if the treatment duration is prolonged or if rinsing is delayed. When caustic scouring interference occurs because of incorrect neutralization, residual alkali remains within the porous lumen of the yarn. Exposure of the alkaline yarn to air leads to localized oxidation of the cellulose molecules.
This decreases the degree of polymerization of the flax, which in turn reduces the tensile strength of the finished linen. Tensile tests on a universal testing machine measure this strength loss, which is recorded in the mill’s daily quality report.
Process Control
Monitoring the washing phase after alkaline treatment prevents the accumulation of salts on the fiber. A pH test of the rinse water provides a measure of neutralization efficiency. If the pH remains above eight after the third rinse, the yarn must undergo an acid-neutralizing wash using dilute acetic acid.
