【纺织课件】SILK FIBERS.ppt

Chapter 11 Silk Fibers Yiping Qiu Introduction The larva of certain insects for use in their building webs, climbing ropes and cocoons Spiders Commercial silk industry: use larva of silkworm Application: Mostly apparel, was also used for parachutes. Structure Macrostructure: Length: 1000-1300 yds (915-1190 m)/cocoon Max 3000yds (2750m)/cocoon, 1 fiber/cocoon. Thickness: 9-11 mm or 1.2-1.5 denier. Varies: thickest in the middle thinnest inside (maybe running out of raw material, or maybe just make itself comfortable). Structure Microstructure cross-section: 2 triangular filaments co-extruded by a worm. The two are called brins held together by sericin (gum or silk glue). Wild silk worms produce ribbon-like silk fibers Structure Submicrostructure Silk from cultivated worm: no identifiable submicrostructure. Wild silk or Tussah silk has internal fibrillar structure. Structure Fibroin protein polymer A chain of amino acids forming a protein called fibroin composed of 15-18 different amino acids. Glycine, alanine and serine occupy 86% of the polymer The side groups of the above 3 amino acids are small compared with those in wool: glycine: R = H alanine: R = -CH3 Serine: R = -CH2OH Crystallize readily: 70-75% Structure Fibroin protein polymer Pack well: lots of H-bonds, small number of ionic bonds No cystine: no S-S bonds Configuration: pleated b-sheet Degree of polymerization of silk DPsilk DPwool Properties For silk producers, i.e. silk worm, spider etc., silk fibers are for protection, transport and food capture Mechanical properties Medium tenacity but higher than wool resulted from molecular structure: zigzag b-sheet of silk vs a-helix of wool higher crystallinity than wool Properties Mechanical properties Medium elongation at break High elastic recovery at low elongation When elongated 2%, 90% elastic recovery Medium modulus Medium abrasion resistance Medium resilience: (cotton silk wool) pleated sheets can slide over one-another. Properties Comfort High h