东华大学：《纺织材料学》课程教学资源（PPT课件讲稿，英文版）Chapter 10 Wool Fibers

Chapter 10 Wool Fibers Yiping Qiu Donghua university

Chapter 10 Wool Fibers Yiping Qiu Donghua University

Morphology A FIGURE 10.2Photomicro graph of wool fiber showing the surface scales overlapping toward the tip of the fiber and an oval cross-section 50μm(eft H 10 um(right)

Morphology

Structures of wool fibers 口 Submicrostructure Cotex core of the wool fiber >90% of the fiber volume consists of countless long, spindle-shaped cells held together by intercellular cement

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

Wool fibers under polarized optical microscope

Structures of wool fibers 口 Submicrostructure Cotex can be divided into 2 sections Orthocotex containing less cystine, and thus less s-s b onas 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 ➢ 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 口 Submicrostructure Cotex: each cortex cell composed of ◆ macrofibril microfibrils protofibril keratin polymer molecules(polypeptide)

Structures of wool fibers ❑Submicrostructure – Cotex: each cortex cell composed 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 ❑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 lonic 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

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 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 of wool fibers ● Comfort properties high heat of wetting due to more amorphous phase than many other fibers slow the rate of evaporation of body water water repellent due to epicuticle 3-D crimp traps more air reducing thermal conductivity air space 2 /3 of total volume low luster due to crimp and scales odor absorbent high pilling but easy to remove

Properties of wool fibers Comfort properties: – high heat of wetting due to more amorphous phase than many other fibers) – slow the rate of evaporation of body water – water repellent due to epicuticle – 3-D crimp traps more air reducing thermal conductivity air space ~ 2/3 of total volume – low luster due to crimp and scales – odor absorbent – high pilling but easy to remove