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 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
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
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
Maintenance of wool fibers
Soil can be easily removed,but may absorb large
quantities of oily soil
Washing:
– wool fibers are weaker in water and have a lower
modulus thus will be easily stretched
– shrinks when agitated in water,felting shrinkage
– degrades in mild alkaline solutions,e.g,detergent
solutions,because alkalinity weakens salt & cystine
linkages and increase felting,dry cleaning
recommended
Maintenance of wool fibers
Washing:
– Bleaches degrades wool and should not be used.
– Dry heat makes fiber brittle
– Relatively high resistance to acid
– Decomposition due to bacteria & enzymes,moths and
beetles harm wool esp,when stained,moth balls and
cedar chests recommended
– Low flammability,self-extinguishes due to high water
content (need high energy to get rid of water)
– chemical absorption,easily absorbs large amount of oil,
good for remove oil spillage or toxic chemicals,
Production of wool fibers
55% produced in Australia,former USSR and New
Zealand
clipped wool or fleece wool,sheared from the sheep
(annually done early spring),better quality
pulled wool,pulled from hide.
chemically shed,falling off in 2 weeks of feeding the
chemical to the sheep
scoured,remove wool grease,suint,sand and some plant
materials (could be 50% of the raw wool)
Lanolin in grease,good for making pharmaceutical or
cosmetic products
Structure of wool
Molecular
structure
Amino Acids
Cystine bond
Tensile behavior of natural
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 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
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
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
Maintenance of wool fibers
Soil can be easily removed,but may absorb large
quantities of oily soil
Washing:
– wool fibers are weaker in water and have a lower
modulus thus will be easily stretched
– shrinks when agitated in water,felting shrinkage
– degrades in mild alkaline solutions,e.g,detergent
solutions,because alkalinity weakens salt & cystine
linkages and increase felting,dry cleaning
recommended
Maintenance of wool fibers
Washing:
– Bleaches degrades wool and should not be used.
– Dry heat makes fiber brittle
– Relatively high resistance to acid
– Decomposition due to bacteria & enzymes,moths and
beetles harm wool esp,when stained,moth balls and
cedar chests recommended
– Low flammability,self-extinguishes due to high water
content (need high energy to get rid of water)
– chemical absorption,easily absorbs large amount of oil,
good for remove oil spillage or toxic chemicals,
Production of wool fibers
55% produced in Australia,former USSR and New
Zealand
clipped wool or fleece wool,sheared from the sheep
(annually done early spring),better quality
pulled wool,pulled from hide.
chemically shed,falling off in 2 weeks of feeding the
chemical to the sheep
scoured,remove wool grease,suint,sand and some plant
materials (could be 50% of the raw wool)
Lanolin in grease,good for making pharmaceutical or
cosmetic products
Structure of wool
Molecular
structure
Amino Acids
Cystine bond
Tensile behavior of natural
fibers
