Apparent Diffusion Coefficients for Reactive Dyes in Swollen Cellulosic Micro Capillaries
Apparent diffusion coefficients dictate internal fiber dye transport rate, governing shade levelness and fixation efficiency in swollen cellulosic processing.
Micro Capillaries
Structural Conduit
Ultrafine void channels located between individual fibrils within the fiber cell wall act as the primary pathways for moisture transport. Micro capillaries are the microscopic spaces that draw water and dissolved chemicals into the fiber interior via surface tension. These channels are far smaller than the macroscopic spaces between yarns or fibers.
They control the rate of chemical absorption and dye diffusion.
Transport Mechanism
Capillary action draws liquids deep into these internal channels without the need for external pressure. The driving force depends on the fiber surface energy and the pore diameter. Smaller diameters generate higher capillary pressures, pulling moisture in rapidly.
This mechanism is responsible for the natural wicking ability of cellulosic fibers.
Finishing Application
Wetting agents and surfactants are applied to reduce the surface tension of water, allowing it to enter the micro capillaries more easily. If these channels remain dry, dyeing will be uneven and incomplete. Proper preparation ensures that the fiber interior is fully accessible to the chemical treatment.
Saturated Limit
In highly crystalline fibers, the volume of these channels is limited, which restricts moisture absorption. Synthetic fibers often lack these micro capillaries entirely, requiring chemical modification to improve their wicking behavior.