News

In textile dyeing, fixatives (also called dye fixatives or mordants) are crucial chemicals used to bind dyes permanently to fabric fibers, ensuring colorfastness during washing, light exposure, and wear. Below is a detailed breakdown of common fixatives and their mechanisms:

Key Types of Dye Fixatives

• Inorganic Salts

Examples: Sodium sulfate, ammonium sulfate.

Function: Adjust dye bath pH and promote dye-fiber ionic interactions. Often used with direct or acid dyes.

• Cationic Fixatives

Examples: Polyquaternium compounds.

Function: Enhance dye adsorption via electrostatic attraction between positively charged fixative and negatively charged fiber/dye.

• Reactive Fixatives

Examples: Epoxy-based compounds, triazine derivatives.

Function: Form covalent bonds with fiber hydroxyl/amino groups and dye molecules, creating a durable link.

• Crosslinking Agents

Examples: N-methylol compounds (e.g., dimethyloldihydroxyethyleneurea, DMDHEU).

Function: Bridge fiber chains and dyes, improving fixation efficiency. Common in cotton reactive dyeing.

• Eco-Friendly Alternatives

Examples: Citric acid, polycarboxylic acids, natural tannins.

Function: Replace formaldehyde-based fixatives, reducing environmental impact while maintaining adequate fastness.

How Fixatives Work

Ionic Bonding: Salts neutralize fiber/dye charges, enabling physical entrapment.

Covalent Bonding: Reactive fixatives create strong chemical links with cellulose (cotton) or protein (wool/silk) fibers.

Crosslinking: Agents form networks that trap dyes within fiber structures.

Fiber-Specific Fixation

Cellulosic Fibers (Cotton): Reactive dyes + alkaline fixatives (e.g., sodium carbonate).

Protein Fibers (Wool/Silk): Acid dyes + metal salt fixatives (e.g., aluminum sulfate).

Synthetic Fibers (Polyester): Disperse dyes + high-temperature fixation (130°C) or carrier chemicals.

Sustainability Trends

Natural Mordants: Aloe vera extracts or tannic acid from plants improve natural dye fixation.

Low-AOX Systems: Fixatives with reduced adsorbable organic halogen compounds comply with eco-certifications like Bluesign®.

Formaldehyde-Free: Citric acid-based systems for wrinkle-resistant finishes.

Example Innovation

Biodegradable Fixatives: Startups like Werewool use coral-derived proteins as colorants and fixatives, eliminating toxic dyes and reducing wastewater pollution.

In summary, dye fixation is a science of balancing chemistry, fiber type, and environmental responsibility to create vibrant, durable textiles. Innovations are continuously emerging to meet both performance and sustainability demands.