Caustic Purification
Alkali treatment removes natural waxes, pectins, and non-cellulosic impurities from grey linen cloth to prepare it for subsequent dyeing or finishing stages. This procedure, known as sodium hydroxide scouring, subjects the textile to a heated solution of sodium hydroxide to induce the saponification of fats and the solubilization of pectic substances. The reaction occurs within large industrial kier vessels or continuous range machinery where concentration, temperature, and duration parameters dictate the removal efficiency.
Precise control prevents excessive degradation of the cellulose polymer chains, which maintains the mechanical integrity of the treated fabric.
Chemical Efficacy
Concentration levels typically range between two and five percent weight by volume, depending on the initial impurity content of the flax fibre. Mill technicians monitor the bath strength throughout the operation to ensure consistent treatment across varying lots of grey cloth. The alkaline liquor penetrates the yarn structure and swells the fibres, forcing out trapped air and particulate matter that would otherwise obstruct uniform dye penetration.
Residual caustic must be neutralized in a later acid wash stage to protect the fibre from damage during prolonged storage or high temperature processing.
Process Verification
Fabric quality at this stage relies on the attainment of specific absorbency standards and residual impurity percentages defined in production contracts. Testing involves measuring the time required for a standardized drop of water to disappear into the cloth surface, a metric commonly referred to as the drop test. A pass result confirms that the sodium hydroxide scouring has rendered the linen sufficiently hydrophilic for consistent chemical application.
High absorbency readings indicate a successful removal of natural lipids, whereas slow absorption signals incomplete chemical treatment or improper rinsing. This technical requirement dictates the baseline for all subsequent colour fastness and finish application in the production line.
