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.
Cellulosic Swelling
Dimensional Change
Intermolecular penetration of water or alkaline agents into the crystalline region of plant fibers causes physical expansion. Cellulosic swelling alters the internal geometry of the fiber by widening the spaces between polymer chains. This expansion increases both the fiber diameter and its chemical accessibility.
Unswollen fibers present tight, impenetrable structures that resist dye molecules.
Chemical Treatment
Concentrated sodium hydroxide solutions induce the highest level of fiber expansion during mercerization. The treatment breaks the hydrogen bonds between cellulose chains and creates new, more accessible sites. This process converts cellulose I crystal structure into the more amorphous and receptive cellulose II form.
Subsequent washing under tension locks the expanded structure in place.
Structural Benefit
Increased dye uptake and improved luster represent the primary commercial advantages of this structural alteration. Swollen fibers absorb larger volumes of moisture and show higher affinity for direct and reactive dyes. This results in brighter shades and less dye waste in the effluent.
The treated fabric also shows better dimensional stability after laundering.
Process Limit
Excessive exposure to highly concentrated swelling agents can degrade the fiber strength. If the treatment duration is not controlled, fiber dissolution begins. This chemical damage reduces the wear life of the finished garment.