Heavy Cotton Duck Dyeing Process Control and Levelness Optimization
Heavy cotton duck dyeing requires progressive electrolyte dosing, high-pressure liquor penetration, and strict tension control to eliminate surface ring-dyeing.
Mercerization Kinetics
Structural Transformation
Rate at which concentrated sodium hydroxide interacts with cellulose determines the degree of swelling and the resulting change in the crystalline structure of the fibre. Study of mercerization kinetics focuses on the time and temperature required to convert cellulose I into the more reactive cellulose II. Molecular transition is responsible for the increased luster and dye affinity observed in treated cotton.
Process Variable
Concentration of the caustic soda and the duration of the immersion are the primary factors governing the speed of the reaction. Lower temperatures generally favor the swelling of the fibre, but they also increase the viscosity of the solution, which can slow down the penetration into the yarn. Balancing these factors is essential for maintaining high throughput on a continuous production line.
Fibre Response
Rapid swelling occurs within seconds of contact, but the complete rearrangement of the molecular chains takes longer. If the fabric is rinsed too early, the transformation of mercerization kinetics is incomplete and the desired properties are not fully realized. Tension must be applied during this phase to prevent the fibre from shrinking and to maximize the alignment of the polymer chains.
Quality Assessment
Measurement of the barium activity number provides an indirect look at how far the reaction has progressed. The value confirms whether the mill has achieved the target level for the specific end-use of the fabric.