文档介绍：Chapter 10 Wool Fibers
Yiping Qiu
Donghua University
Morphology
Structures of wool fibers
Submicrostructure
Cotex
core of the wool fiber:
90% of the fiber volume,
consists of countless long, spindle-shaped cells held together by intercellular cement
Wool fibers under polarized optical microscope
Structures of wool fibers
Submicrostructure
Cotex
can be divided into 2 sections:
Orthocotex containing less cystine, and thus less S-S bonds
Paracortex containing more cystine, absorbing less water.
two sections spiral around each other along the fiber length.
the two sections respond to heat and moisture differently forming 3-D crimp.
Structures of wool fibers
Submicrostructure
Cotex: each cortex posed of
macrofibrils
microfibrils
protofibrils
- keratin polymer molecules (polypeptide)
Structures of wool fibers
Keratin polymer: helix of amino acids
Structural characteristics
18 different amino acids: each with -N-C-C- backbone
a helix: 3 amino acids per turn (right-handed helix)
Diversity of amino acids: good for dyeing
Polar groups in amino acids: hydrophilicity
Cystine amino acid: contains sulfur: degradation by moths and beetles
Big side groups and spiral molecular configuration: hard to be packed well leading to low crystallinity (only 25-30%)
Structures of wool fibers
Intermolecular bonding
Cross-linking: 2 cystine amino acids one on each of the two adjacent chains form a cystine link, a covalent bond (S-S bond), increasing strength and elasticity.
Ionic bond: salt linkage formed when two amino acids are in close proximity: responsible for reacting with acid dyes.
Hydrogen bonds: between amide groups but have relatively low density due to more amorphous phase and packing difficulties.
Properties of wool fibers
Mechanical properties:
relatively low strength or tenacity
high elastic recovery
high flexibility
high resilience
low initial modulus
low abrasion resistance
low stiffness
low toughness
properties change as water absorption changes
Properties