Physical Phenomenon
Fluid flow driven by surface tension gradients along an interface causes local movements of liquid and dissolved chemicals. In wet textile processing, Marangoni convection occurs during the drying stage when local temperature differences or chemical concentrations change the surface tension of the pad liquor. This flow can distribute dye particles unevenly across the yarn surface before fixation.
System Mechanism
Evaporation causes temperature drops that are non-uniform across the fabric surface due to uneven yarn structures. Areas with higher evaporation rates cool down faster, raising the surface tension in those zones. Liquid flows from the regions of lower surface tension to those of higher surface tension, carrying dye particles with it.
This local movement alters the distribution of dye across the yarn cross-section, which creates micro-shading defects in the finished fabric.
Operational Control
Adding surface-active agents to the pad bath balances the surface tension across the entire wet area. Minimizing this temperature-induced Marangoni convection requires gentle, uniform drying in the pre-dryer to avoid localized hot spots. Technicians adjust the air nozzle configuration to ensure even thermal distribution across the fabric width.
Infrared sensors monitor the temperature profiles of the fabric to prevent localized evaporation spikes.
Process Constraint
This convection is difficult to eliminate in blended fabrics where different fibres create varying surface chemistry and evaporation rates. It remains a major challenge in high-speed lines where rapid heating is necessary to maintain production rates.
