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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