Thermodynamic Modeling of Bifunctional Dye Hydrolysis under High Shear Boundary Layer Flow
High fluid shear compresses boundary layers, accelerating hydroxyl mass transfer and driving hydrolytic dyestuff loss in bifunctional reactive dyeing.
Micro-Fibril Swelling
Structural Expansion
Volumetric expansion of the internal crystalline and amorphous regions of a natural fibre occurs when water molecules penetrate the primary structure. This physical change opens the spaces between the long-chain molecules, which is essential for the entry of large dye molecules. Without micro-fibril swelling, the interior of the fibre remains inaccessible, and the dye only coats the outer surface.
Internal Access
Saturation of the textile material in an aqueous bath triggers the opening of the fibre architecture. The degree of micro-fibril swelling is influenced by the temperature of the liquor and the presence of certain chemicals such as caustic soda. In mercerization, this expansion is maximized to permanently alter the lustre and dye affinity of the cotton yarn.
Moisture Influence
Fiber diameter increases notably as the internal voids fill with solvent. This change affects the tension of the fabric within the machine and must be accounted for during the winding and transport phases of production.
Processing Impact
Control over the rate and extent of the expansion ensures that the dyeing remains level from the beginning to the end of the batch. Excessive micro-fibril swelling can lead to fabric stiffness or loss of strength if the chemical environment is too aggressive for the specific fibre type.