Animal Fibre Wool

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Animal FibreWool

• The variety of fleece material
• Fleece consists of two parts
• an outer coat of long, course and hairy fibres,
• and a soft, downy under coat which is soft and
  fine.
• A wide variety of fibres can be found in a
  single lock of wool. They also vary in
  character according to their position on the
  animal body. The shorter coat is valued for its
  softness, whiteness and warmth while outer coat
  because of its colour, harshness and unlikely
  feel is not so desirable. Therefore careful
  breeding is important to produce uniform quality
  of wool throughout the fleece.
• wool classing
• Wool classing is a process in which fleeces
  obtained are separated into different classes
  according to their character so that the maximum
  degree of uniformity can be achieved.

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Type of wool
Wool name Fleece Region Characteristics Length Cross-section uses
Mohair Angora goat U.S.A., South Africa, Turkey Long length, softness, Springy nature, excellent luster, very little ability to felt 4-10 inches 25-55µ vast variety of textiles
Cashmere Tibetan goat Tibet Downy handle, fluffy nature, brown or grayish white colour 1.5 3 inches 15 µ shawls
Alpaca Peruvian goat or llama Peru, Bolivia Brown, gray or black in colour 10 inch 10 35 µ lining or mens wear
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Wool fibre morphology

• Macro-structure of wool
• wool is a crimped, fine to thin, regular fibre.
  Finer wool has 10 crimps/10 centimeter while
  coarser wool has 4 crimps/10 centimeter. As
  diameter of the fibre increases the no of crimps
  per unit length decreases.
• Under the microscope the appearance of wool is
  over-lapping surface cell structure. These cells
  are known as epithelial cells and commonly called
  scales point towards the tip of the fibre. The
  scales give fibre a serrated surface. The
  cross-section of fibre is oval in shape.
• length of the fibre ranges from 5cm for finer
  wool to 35 cm for longest and coarser wool. For
  textile manufacturing 5 12 cm is preferred.
• Fibre length to breath ratio is 25001 for finer
  wool and 75001 is for coarser wool.
• wool fibre may vary from off-white to light
  cream in colour. This is due to the presence of
  disulphide bonds. When fibre is cream to dark in
  colour it is due to the degradation of fibre
  surface as wool fibre is very sensitive to
  atmospheric oxygen and air pollution.

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Felting

• Irreversible shrinkage of length , breadth or
  thickness of material.
• It is done by agitation in an aqueous solution.
• Disadvantageous for woollen laundering.
• It is done by over lapping epithelial cells or
  scales.
• Less friction will result in rootward direction
  than in tipward direction.

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DFE

• Difference in direction friction called DFE
• This movement caused by agitation and moisture.
• Felting can be enhanced by heat, acid and
  alkalis.
• Heat will make fiber elastic, plastic, distort
  and entangled itself with other fibers.

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Micro-structure

• Wool fibre is a highly complex skin tissue. The
  micro structure consists of three main
  components
• The cuticle
• the cuticle is the over-lapping epithelial cells
  surrounding the wool fibre. Epithelial cell is 1
  µm thick, 30 µm long and 36 µm wide. It consists
  of
• epicuticle out-most layer or sheath which covers
  the fibre, it is only a few molecules thick and
  is composed of a water repellent, wax-like
  substance. It also has countless microscopic
  pores which allows fibre to absorb moisture.
• exocuticle the overlapping epithelial cells
  also form exocuticle. About 10 µm epithelial cell
  can be seen in finer fibre and 20 µm epithelial
  cell can be seen in coarser fibre.
• endocuticle. Is the cementing layer bonding the
  epithelial cells to the cortex of the wool fibre.

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• Cortex
• cortex or core of the fibre forms about 90 of
  the fibre volume. It consists of long
  spindle-shaped cells thick at the middle. These
  cells are about 100 200 µm in length, 2-5 µm
  wide and 1-3 µm thick. Finer wool have around 20
  such cells while coarser wool has 50 cells across
  the diameter. Cortex is composed of two distinct
  sections.
• Ortho-cortex and para-cortex para-cortex
  contains more cystine content than ortho-cortex.
  They spiral around one and other along the length
  of the wool fibre. Para-cortex tend to be on the
  inside of the spiral. This explains the crimp
  configuration of wool fibre. Para-cortex being
  rigid and stable tend to tighten the spiral while
  ortho-cortex elastic and flexable conforms spiral
  to the outer side.

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• Fibril
• The cortical part consists of number of
  macro-fibrils, each about 100 200 nm in
  diameter. These micro-fibril are held together by
  a protein matrix. Each macro-fibril is consists
  of hundred of micro-fibril each about 5 nm in
  diameter. Each micro-fibril consists of eleven
  protofibril about 500 nm in length and 2 nm in
  diameter. The proto-fibril spiral about each
  other. Finally each proto-fibril consists of
  three wool polymers which also spiral around each
  other.
• It is this spiraling structure which contribute
  towards the elasticity, flexibility and
  durability of wool fibre.

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Wool polymer system

• Wool polymer is linear, keratin polymer, with
  some very short side groups and has normally a
  helical configuration.
• The repeating unit of wool is amino acid. Amino
  acids are linked to each other by peptide bond
  i.e. CO-NH- to form wool polymer.
• The wool polymer is composed of twenty amino
  acids so the general formula for wool polymer is
  R-CH(NH2)-COOH. In general, arginine, cystine,
  glutamic acid constitute the one-third of wool
  polymer.
• Helical configuration is called alpha-keratin and
  extended configuration is called beta-keratin.
• Hydrogen bonding is the inner polymer forces of
  attraction. Secondly, salt linkages or ionic
  bonds also form between side groups such as
  between carboxylate group (-COO) and amino group
  -NH3
• The cystine sulpher containing amino acid forms
  cystine linkages or disulphide bonds. These
  linkages are very strong as they are covalent
  bonds. They occur within and between wool
  polymers.
• There are also van der Waals forces present but
  other forces tend to make these forces
  insignificant.
• Each proto-fibril consists of three alpha-keratin
  spiraling about each other.
• Eleven proto-fibril spiral about to form one
  micro-fibril while hundreds of micro-fibril
  spiral about each other to form one macro-fibril
• The polymer system is 70-75 amorphous and 25-30
  crystalline, the spiraling does not indicate a
  well aligned polymer system.

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Properties

• Tenacity
• The low tensile strength of wool is due to
  relatively weak hydrogen bonding. The lack of
  strength is compensated by alpha/beta keratin
  configuration.
• When wool fiber absorb moisture, the water
  molecules force sufficient polymers apart to
  cause a significant number of hydrogen bonds to
  break. In addition the water molecules also
  hydrolyse the salt linkages. The breakage of
  hydrogen bonding and hydrolysis of salt linkages
  cause wool fibre to swell and result in loss in
  tenacity of wet wool textile material.
• Elastic nature
• Wool has good elastic recovery and excellent
  resilience. The ability of wool fiber to recover
  is partly due to its crimped configuration and
  partly due to its alpha-keratin configuration of
  polymer. The ability of polymer to return its
  alpha-keratin configuration is due to
  inter-polymer disuliphide bonds, salt linkages
  and hydrogen bonding.
• Hygroscopic nature
• The absorbent nature of wool is due to the
  polarity of peptide group, the salt linkages and
  the amorphous nature of its polymer. The peptide
  group and salt linkages attract water which
  readily entres the amorphous region of wool
  fibre.
• The dry wool may develop static electricity. This
  is because there is not enough water molecules
  present in the polymer system to dissipate static
  charge.

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• Heat of setting
• Wool is renowned to give up small steady amount
  of heat while absorbing moisture. This is know as
  heat of setting. This is due to the energy given
  up by the collision between polar molecules and
  water. Wool fabric have much less chilling effect
  on the skin in comparison with other textile
  materials. This is because wool polymer will
  continue to give off heat until it become
  saturated with water molecules.
• Thermal properties
• wool is poor conductor of heat and has low heat
  resistance. There is no satisfactory explanation
  for this except that when wool absorb large
  amount of heat the disulphide linkages break. And
  polymer fragmentation occur. Initially this
  fragmentation will only result in discoloration
  of wool fibre. Prolong exposure to heat can
  result in scorching. The brown and black colour
  of wool fibre is due to formation of minute
  particles of carbon.
• Wool smoulders rather than burns. This seems to
  be due the water molecules held by hydrogen bonds
  to the polymer sites on the keratin polymer.
  Therefore if wool is exposed to naked flame, much
  of the heat or kinetic energy is consumed in
  producing steam.

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Chemical properties

• Effect of acids
• Wool is more resistant to acids than to alkalis.
  Acid hydrolyze the peptide group but leaves the
  disulphide group. The polymer weakens but does
  not dissolve though it become very vulnerable to
  further degradation. it is essential to
  neutralize wool after acid treatment.
• Effect of alkalis
• Wool dissolve readily in alkaline solution.
  Alkali dissolve the hydrogen bonds, disulphide
  bonds and salt linkages. Prolong exposure to
  alkies cause fragmentation and complete
  destruction of wool fibres.
• Effect of bleaches
• No method is known for bleaching wool
  permanently. The effective method of bleaching
  wool is to use a reducing bleach followed by an
  oxidizing bleach. Reducing bleach such as sodium
  bisulphite, sodium sulphite converts
  discoloration on the fibre surface to colourless
  compounds. Due to the application of oxidizing
  bleach the colourless compounds are converted
  into water soluble compounds and then can be
  rinsed off.
• Effect of sunlight and weather
• Sunlight cause yellowing or dullness of wool
  fabric. The ultraviolet rays of sunlight degrade
  the peptide and disulphide linkages
  degradation products cause wool fibre to absorb
  more light and to scatter the incident light even
  more to give yellowing or dulling effect on
  fabric.