Definition
Alkalization refers to the deliberate raising of the pH of an aqueous solution or a textile substrate by adding alkaline agents such as sodium hydroxide, sodium carbonate, or sodium silicate. The process shifts the chemical equilibrium into the basic range (pH above 7) and alters the surface charge as well as the swelling behavior of the fibers. Alkalization is a deliberately controlled process and must be distinguished from unintentional alkalization, which may occur as an unwanted side effect in production processes.
Use in the textile industry
In the textile industry, alkalization is used primarily in the dyeing and printing of cellulosic fibers, since reactive dyes bond covalently with the fiber under alkaline conditions, producing a permanent coloration. Alkalization with concentrated sodium hydroxide solution is also applied during the mercerization of cotton to swell the fiber structure, increase luster, and improve dye uptake. In addition, alkalization serves as a pretreatment step — for example during scouring or bleaching — to saponify and remove soil, sizing agents, and fatty components.
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