The variety of fleece material
1.
2.
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.
Wool name Fleece
Region
Characteristics
Length
Crosssection
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
men’s
wear
Macro-structure of wool
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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 2500:1 for
finer wool and 7500:1 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.
 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.
 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.
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.
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.
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 protofibril 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 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 (-COOˉ) 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.
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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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.
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