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Natural Protein Fibre
All proteins are polymers of amino acids.
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Definition: The protein fibers are formedby natural animal sources through
condensation of amino acids to form
repeating polyamide units with various
substituent on the carbon atom. The
sequence and type of amino acids making up
the individual protein chains contribute to the
overall properties of the resultant fiber.
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Side groups in protein fibre.
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Cross links
Cross-links are bonds that link one polymerchain to another. They can be covalent bondsor ionic bonds.
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Wool quality number
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Morphology of wool
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Chemical composition of wool
comp. %
Keratin 45- 75
Grease 5 -15 Moisture 10 12
Suint 2 12
Sand & dirt 4
30 Vegetable matter 0 - 5
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Protein as a ampholytes
Ampholytes are molecules containing both
acidic and basic groups.
All of the common amino acids found in
proteins are ampholytes because they contain
a carboxyl group (-COOH) that acts as an acid
and an amino group (-NH2) that acts as a
base.
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Composition of wool keratin
Carbon 50.3 to 52.5
Hydrogen 6.4 to 7.3
Nitrogen 16.2 to 17.7 Oxygen 20.7 to 25.0
Sulphur 0.7 to 5.0
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Keratin : it is form by 15 to 20 amino acids
gets condensed with each other and form
polypeptide chains with condensed matterand COOH Group.
Grease : it is soluble in organic solvents like
ester of fatty acids or monohydric alcohol. Suint : it is soluble in water and can be
isolated form wool by aqueous extraction.it
consist of potassium salt of fatty acids andorganic amino acids.
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Physical properties of wool
Length (3.6 cm to 15 cm)
Cross-section circular to elliptical
Crimp
0 to 30 cirmps per inchfine 14 -22 , medium 8 -14 and course 8
Breaking strength:
fine 4.8 to 10 gm, medium 10
16 gmand for course 20 24 gm
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Wool is hydroscopic in nature
its moisture content 12 to 15 % at 60 % RH
And at RH 70 to 80 % moisture content is 17 to
18 %.
Electrical conductivity: bad conductor of
electricity.
Burning : it catechus fire and burn.
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Action of heat:
Heat at 1000
C over a long period it losesmoisture and fibre becomes harsh loses
strength.
If it returned to moist air again absorbs moisturerapidly.
If the 100 0C is exceeded any length of time it
decompose will acquire yellow color.
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Effect of water and steam
wool changes its shape and affinity to dye when exposed to
water or steam.
Wool size increased in cold or hot water but on drying again
return to its own size.
Plastic property-
if wool is in dry state is deformed by imposing some fibre will
recover its strain fibre will recover its original form.
As humidity increases
Wool loses its rigidity almost completely in boiling water become
highly plastic.
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Action of acid
Wool absorbs an acid from soln of acid and holds it
firmly even after washing with water due to some
amino groups.
Nitric acid
color changes to bright yellow Dilute acid prolong heating causes to hydrolysis of
keratin to a mixture of amino acids.
Hydrolysis of peptide linkages results in formation offree carboxyl group. Which increases the capacity of
wool to combine with acids.
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Wool react immediately with HCl & H2 So4 and
become brittle and hard, surface scales of
fibre are all deformed. It loses all desirable
properties of wool.
Dilute mineral acid changes its appearance
but not causes changes in physical properties,
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Action of Alkalies
Action of caustic soda or NaOH- 5 % soln
completely dissolve wool in few min at boiling
temp.
Strength of wool increases when treated with
15 % NaOH at 19 0C for 5 min.
Strong Alkali may act in diff way
it hydrolyse main polypeptide chain of protein
breaking them down in salt of amino asid.
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Action of Oxidising agent
Strong Soln of H202, K2Cr2O7 damage wool
more or less depending on temp and PH.
Oxidising agent attack disulphide group of
Cystine resulting in lower strength weight loss.
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Action of Reducing agent
Reducing agent attack keratin group,
disulphide group forming sulphydryl group
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Effect of sun light and age
UV rays of the sun cause breakage of the
disulfide bonds of cystine which results in
photo chemical oxidation. This causes
degradation and, if exposure is prolonged,
eventual destruction. However wool has
better resistance to sunlight than cotton.
No sever effect of age if stored after cleaning.
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Biological properties
Wool has resistance to bacteria and mildew.
But the stains on wool attacked by them and
destroy fibre.
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Chemical modification in wool fibre
As wool is a protein and readily considered as a food for
several types of insects.
Thus it is necessary to prevent wool fiber from these insects.
Some chemical are applied on wool fibre that will kill the
insects. These finishes need frequent renewing , washing dry-
cleaning removes it.
Thus some chemical are applied that react with the wool and
change molecules of wool and makes them uneatable to
insects. These chemical are durable to wash and dry cleaning.
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Use and care of wool
Wool has high crease recovery and elasticity when it
is dry and lower when it is wet.
So dry-cleaning and pressing of wool is easy but
washing is not easy.
Chlorine bleaches can not be use for bleaching, as
they break cystine linkages and damage fibres. For
bleaching hydrogen peroxide can be used.
Mild soap and detergents are used for washing.
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Some wool fabrics are labeled as washable.
These fabrics are finished with some special
finish or nylon fibres are mixed with wool
fibres. So these fabrics should not wash withhot water.
Store after cleaning and washing
Finish effect on scales.
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Books
Textile science by E P G Gohl
Introductory Textile science M L Joseph
Textile fibre H V S Murthy
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