1. Covalently graft stable anionic sulfonate dye binding sites
Sodium allyl sulfonate (SAS) copolymerizes with acrylonitrile via its allyl double bond, permanently fixing negatively charged −SO3− groups onto PAN polymer chains.
These strong-acid sulfonate groups remain fully ionized in acidic dye baths (pH 2–7), unlike carboxyl monomers that lose negative charge under acid conditions. The abundant fixed negative sites strongly attract positively charged cation dyes and form stable ionic bonds, greatly raising dye adsorption capacity and color saturation.
2. Loosen compact PAN crystalline structure to boost dye penetration
Pure polyacrylonitrile has dense, tightly stacked molecular chains with tiny internal voids, blocking dye liquor infiltration.
Hydrophilic sulfonate side chains inserted by SAS break ordered crystal stacking, increase free volume inside fiber cross-section. Dye solution quickly diffuses into fiber core instead of only staying on the surface, eliminating floating color and uneven shade.
3. Anti-interference against water hardness cations
Sulfonate anions have strong anti-shielding ability toward Ca2+,Mg2+ in industrial hard water. Hardness ions cannot neutralize the negative charge on fiber surfaces, so dye uptake stays consistent without color variation in regular factory dyeing water.
4. Realize uniform level dyeing across fiber batches
SAS evenly distributes along polymer backbones during copolymerization, forming homogeneous anion sites on every fiber filament. All fibers absorb dyes at the same rate, avoiding barreling, speckles and color difference between yarn sections.
5. Enhance permanent color fastness
The ionic bond between grafted sulfonate groups and cation dyes is firm and not easily broken by water washing or friction. Dyes are locked inside fiber molecular network, significantly improving washing fastness, rubbing fastness and light fastness of finished acrylic textiles.
