Silk Fibre Structure and Chemistry
topic
Silk structure: continuous filament (bave) consisting of two fibroin filaments (10-13 μm diameter each, core protein composed of glycine 43%, alanine 30%, serine 12%—creating β-sheet crystalline structure 50-60% crystallinity) glued together by sericin protein (serine-rich, 20-30% of cocoon weight, water-soluble gum removed in degumming). Molecular structure: fibroin heavy chain (350 kDa) with repetitive sequence (GAGAGS) forming anti-parallel β-pleated sheets providing strength, and amorphous regions providing elasticity. Cross-section: triangular prism shape (creating light refraction—luster), diameter 10-13 μm for mulberry, 20-40 μm for wild silks, density 1.33-1.40 g/cm³.
Role
β-sheet crystalline structure provides silk's exceptional strength (tensile 300-500 MPa, comparable to steel wire of same diameter) and thermal stability (decomposes >170°C without melting), while sericin removal during degumming reduces weight 20-30%, increases softness, and reveals characteristic luster through triangular cross-section refracting light.