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Wool Fibre
1. GROWTH AND MOLECULAR STRUCTURE OF WOOL FIBRE ;
PHYSICAL AND CHEMICAL PROPERTIES OF WOOL.
By: Supriya S.Deokar
M.V.Sc Scholar
Department of Livestock Products
Technology
2. INTRODUCTION
Fleece obtained from sheep =Raw/Grease wool.
It is the animal fibre which grows from follicles
in the skin .
Indian needs good wool & increased supply of
mutton .
Population of sheep -71.6 million (4th rank)
The yield of wool -350 gm to 1800gm/sheep/year
Mohair-Straight ,uneven ,translucent fibre
obtained from Goat.
3. CHEMICAL STRUCTURE OF WOOL FIBRE
Wool fibre is a protein known as keratin. Keratin is
made up of amino-acids joined by peptide linkages.
In addition to carbon, hydrogen, oxygen and nitrogen it
also contains sulfur. These 5 elements are combined
into 19amino acids linked together in ladder-like
polypeptide chains.
The amino-acids present in wool are mainly bulky, while
silk has chiefly small amino-acids. Due to this wool is
relatively amorphous. The polymer system of wool is
highly amorphous that is 75%
Wool fibres-2 cell typesCuticle and cortex cell
Central medulla is present .
8. Stage F1: Follical plug –
A plug of cells from Epidermis into Dermis
-This stage begins when a localized thickening of the
basal of the epidermis can be recognized.
Stage F2: Pre-papilla- The base of epidermal plug
flattens prior to invagination
Stage F3: Papilla –epidermal plug invaginated and dermal
papilla is formed.
Stage F4: Hair cone –The elongated the cells of Henle’s
layer of the inner root sheath are recognized, forming a
cone which is directed along the axis of the follicle
towards the skin surface.
Stage F5: Advanced hair cone –The tip of the hair cone
reaches the deepest level of sebaceous gland
9. Stage F6: Hair formation –The tip of keratinized hair
fibre inside the hair cone.
Stage F7: Hair in epidermis-The tip of the keratinized
hair reaches beyond the base of eipdermis above the
follicle .
A hair canal has usually been formed in the epidermis
before the hair tip reaches the level
Stage F8: Hair emerged –The tip of the hair has been
penetrated the superficial layers of the epidermis .
10. PHYSICAL PROPERTIES OF WOOL
Hydroscopic nature:
-It has the very absorbent nature because of the polarity
of the peptide group, the salt linkages and the amorphous
nature of the polymer system. The peptide groups and salt
linkages easily attract water molecules which enter the
amorphous polymer system of the fibre.
Density:
-It has a comparatively low density and therefore fibres
are light with regard to their visible weight.
Luster:
It is ability of wool to reflect light.
Softness:
-Soft wool produces fabrics softer to touch .
Non-Inflammable:
-Slower to burn and on burning it gives off a pungent
odour and forms bead where burning ceases.
11. Elasticity and resiliency:
-This is elastic and resilient. Covalent bonds can stretch,
but they are strong. The disulphide bonds in the
amorphous parts of the strand or fibre are able to stretch
when the strand is extended. When the strand is released
the disulphide bonds pull the protein molecules back into
their original positions.
Conductivity:
-is best of fibre holding in body heat and also keeping
heat out.
-It has a low conductivity of heat and therefore makes
it ideal for cold weather.
Strength :
-Wool fibres and fabrics are usually strong and durable.
12. CHEMICAL PROPERTIES OF WOOL
Effect of acids:
-Concentrated acids damage it since they hydrolyze the
salt linkages and hydrogen bonds. Dilute acids do not
affect it.
Effect of alkali:
-It easily dissolves in alkaline solutions. Alkalis hydrolyze
the disulphide bonds; hydrogen bonds and salt linkages of
wool and cause the polymers to separate from each other,
which is looked as dissolution of the fibres.
Prolonged exposure of Alkalis On wool Hydrolysis of
peptide bonds polymers Fragmentation destruction of
the fibre
13. Effect of bleach:
-Chlorine bleach is ordinary harmful to the wool.
KMnO4, Na2O2 are utilized for bleaching.
Effect of sunlight and weather:
-Effect of sunlight’s ultra-violate radiation tends to
yellow white or dull colored fabrics.
-The UV cause the peptide and di-sulphide bonds to sever.
This leads to polymer degradation products on the surface
of the fibre. As a consequence the strand not only
absorbs more light but scatters the incident light to a
greater extent.
-Prolonged exposure sunlight weakens the fibres very
much.
14. Colorfastness/Dyeing properties :
-Like cotton wool is easy to dye. Acid dyes, chrome and
mordant dyes are utilized to dye this. The dye molecules
are attracted into the amorphous areas of wool.
