Laboratory Assay
Analytical measurement of active sodium hydroxide concentration in a mercerizing bath provides the primary means of ensuring consistent treatment of cotton yarns. This specific procedure, known as alkali liquor titration, utilizes a standardized acid solution to neutralize a filtered sample of the bath. It establishes the exact chemical strength of the process bath before the fabric enters the wet finishing line.
Chemical Mechanism
Neutralization occurs when a known volume of hydrochloric or sulfuric acid reacts with the dissolved sodium hydroxide until a distinct pH endpoint is reached. During alkali liquor titration, a phenolphthalein indicator changes from pink to colorless at a pH of approximately 8.3, marking the completion of the primary reaction. A secondary titration using methyl orange can determine the level of carbonate contamination within the same bath.
Carbonate accumulation reduces the effectiveness of the treatment.
Industrial Application
Mercerizing mills run these tests at scheduled intervals to prevent under-treated fibers or wasted chemicals. When alkali liquor titration is executed on the factory floor, operators can calculate the precise volume of concentrated caustic needed to replenish the bath. This control loop secures uniform luster and prevents dye affinity variations in the finished knit fabric.
Consistent dye uptake depends on this bath density.
Process Margin
Excessively high concentrations can degrade delicate fibers. Through alkali liquor titration, the mill maintains the bath within a narrow band of sodium hydroxide concentration. Deviation from this window results in uneven yarn shrinkage.
