Methacrylamide (MAA) is widely adopted in silk processing to offset the 20%-30% weight loss during degumming—where impurities like wax and pigments are removed. By grafting MAA polymers onto silk fibroin, manufacturers achieve targeted weight gains while improving fabric drape, texture, and durability.
Technical Process of Silk Weight Gain
The grafting occurs through free-radical polymerization under controlled conditions:
1. Pretreatment: Degummed silk yarns or fabrics are immersed in an aqueous MAA solution.
2. Initiation: Adding catalysts like potassium persulfate (KPS) and formic acid (pH 3) generates reactive sites on silk fibroin chains.
3. Grafting: At 80–85°C, MAA monomers covalently bond to silk’s amorphous regions. Key parameters include:
- MAA concentration: 60%–300% (on weight of fiber)
- Time: 40–90 minutes
- Bath ratio: 1:20–1:50.
4. Post-treatment: Washed and dried silk exhibits up to 60% weight gain while retaining natural luster and softness.
Impact on Silk Properties
- Physical Performance:
- Weight gain enhances fabric density, drape, and wrinkle resistance.
- Surface roughness slightly increases, but tensile strength improves by ~15%.
- Dyeing Behavior:
Grafting reduces amorphous areas, lowering dye adsorption. Reactive dye fixation decreases proportionally with MAA concentration, making deep shades challenging.
- Structural Integrity:
FTIR and XRD analyses confirm MAA modifies silk’s non-crystalline zones without altering crystalline structures or backbone conformations.
Quality Control Innovations
Advanced methods ensure precise weight gain:
- Thermogravimetric Analysis (TGA): Measures characteristic peak ratios (285°C for MAA polymers vs. 324°C for silk) to calculate grafting percentages. A linear model `y = 1.012x – 0.838` correlates peak area ratios with weight gain (R² > 0.99).
- Infrared Spectroscopy: Monitors the 1,205 cm⁻¹ absorption band—a signature of grafted MAA polymers.
Advantages Over Traditional Methods
Unlike tin weighting or tannin treatments, MAA grafting:
- Avoids heavy metal toxicity and fiber embrittlement.
- Uses safer, non-azo dyes (validated by eco-certifications).
- Enables customizable weight increments via dosage adjustments.
Conclusion
Methacrylamide grafting merges economic value with performance enhancement in silk processing. Its water-soluble, controllable nature aligns with sustainable textile demands, though dyeing modifications remain needed for dark shades. As research advances—like Zhejiang’s 2014 industrial-scale success—MAA continues to redefine silk’s luxury appeal through science.
Post time: Aug-15-2025