文档介绍：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 - denier.
Varies: thickest in the middle thinnest inside (maybe running out of raw material, or maybe just make fortable).
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 posed 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 pared 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, . 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 heat of wet