Silk Tensile and Degumming Loss Testing

Silk tensile testing (single fibre or yarn, Textechno Favimat+ or Instron 5965, gauge length 20 mm, extension rate 2 mm/min, pretension 0.1 cN/tex) measures filament tenacity (35–50 cN/tex for degummed Bombyx mori fibroin, 25–40 cN/tex for tussah silk), elongation (15–25% for Bombyx, 25–35% for tussah with more β-sheet crystallinity variation), initial modulus (5–12 GPa), and work of rupture (energy absorption per unit mass). Silk fibroin tensile strength derives from β-sheet crystalline domains (alanine-glycine repeat sequences, crystal dimensions 5 × 6 nm, crystallinity 40–60% by WAXD) interconnected by amorphous glycine-rich regions — tensile modulus correlates with crystallinity (R² = 0.89). Degumming loss test (ISO 6940 sericin removal: 2 g raw silk in 250 mL solution of 2 g/L NaOH + 2 g/L surfactant, 95°C, 30 min, rinse, dry 105°C — degumming loss% = (initial weight − degummed weight) / initial weight × 100): Bombyx mori raw silk degumming loss 22–28%, tussah 12–18%. Commercial trade implication: if raw silk buyer pays $30/kg for 25% gum content, effective fibroin cost = $30 / 0.75 = $40/kg — degumming loss testing prevents adulteration (artificial weighting adding mineral salts to raw silk was common historically, now detected by ash content >0.5% indicating weighting). UV degradation testing (xenon arc ISO 105-B02, 100 kJ/m²): silk loses 40–60% tenacity after 200 kJ/m² UV exposure — photodegradation of tyrosine chromophore in silk fibroin at 280–310 nm — important for heritage textile conservation assessment and product lifespan prediction in high-UV-exposure apparel.