Oxidizing Capability
A chemical metric quantifies the concentration of oxidizing chlorine species available in a bleaching bath or sanitizing solution. In textile processing, active chlorine content determines the bleaching efficiency of sodium hypochlorite solutions used to whiten cotton fibres. This parameter represents the total oxidizing power of the bath expressed as an equivalent mass of elemental chlorine.
Titration Method
Measuring the parameter typically requires iodometric titration using sodium thiosulfate in an acidic medium. The chemical test utilizes potassium iodide, which reacts with the active chlorine content to liberate free iodine in direct proportion to the oxidant present. A starch indicator is added, and the solution is titrated until the blue color disappears entirely, providing a precise volumetric measure of the available chlorine.
This titration must be executed immediately after sampling to avoid natural volatilization or thermal decomposition of the unstable chlorine species.
Bleaching Action
Bleaching of natural cellulosic fibres relies on the controlled oxidation of natural pigments. If the concentration of active chlorine content is maintained within narrow limits, it removes impurities without attacking the underlying polymer structure of the cellulose. Excessive concentrations, however, lead to uncontrolled oxidation and severe strength loss in the finished goods.
Degradation Threshold
Uncontrolled exposure to highly concentrated solutions damages the molecular structure of the cotton. This damage appears as a sharp reduction in tensile strength and a decrease in the degree of polymerization of the cellulose chains. Standard procedures therefore dictate frequent monitoring of the bath to prevent fibre degradation.
