Quantifying Radial Fixation Gradients in Ultra High Twist Viscose Ply Yarns under Dynamic Alkali Steaming
Dense viscose ply yarns require controlled swelling alkali blends to eliminate core fixation gradients during dynamic steam fixation.
Core Sheath Color Disparity
Structural Defect
Structural variations in synthetic yarns produce shade differences across the cross section of individual filaments. This phenomenon of core sheath color disparity occurs when dye molecules fail to penetrate into the filament center, leaving the outer sheath heavily shaded while the inner core remains light or undyed. Chemical ring dyeing in polyester or nylon fibers creates this uneven optical appearance.
Laboratory microscopic cross sectioning exposes the boundary where dye penetration halts.
Optical Assessment
Light transmission through cross sectioned fibers reveals differences in absorbance between the exterior ring and interior center. High contrast between regions alters total color yield during spectrophotometric measurement. Light scattering from the pale core dilutes the perceived depth of shade on finished fabric surfaces.
Microscopic image analysis quantifies the radius of the outer dyed ring against total fiber radius.
Processing Mechanism
Rapid cooling during filament extrusion generates high orientation in the outer sheath layer, which restricts dye diffusion during heat setting and exhaustion. Rapid dyeing cycles exacerbate core sheath color disparity by shortening the time available for dye molecules to move past initial surface fixation sites. Carrier additives open the polymer structure to allow full penetration.
High temperature exhaustion holds dye liquor at peak energy levels until equilibrium occurs across the entire filament profile.
Commercial Tolerance
Fabric buyers reject lots exhibiting ring dyeing because wet abrading or severe rubbing exposes the pale filament core, creating frosty patches on garment surfaces. Inspection protocols require cross section checks on heavy shades.