natural fibres

Natural Fibres• Cotton• Silk• Wool• Linen

COTTON

• Cultivation• Morphological structure• Chemical structure

Commercial classification of Cotton based on the length of the fibre

• Sea Island cotton – 5 cm or more• Egyptian cotton – 3.7 - 4.5 cm• Brazilian cotton – 3 - 4 cm• American cotton – 2.5 - 3.5 cm• Indian cotton – 2 - 3 cm• Chinese cotton – 1.5 - 2 cm

Diameter of cotton fibre = 15-20 microns

Morphological structure of Cotton

Convolutions

Lumen

The morphological structure of the fibre consists of 4 parts:a. Cuticleb. Primary wallc. Secondary walld. Lumen

a. Cuticle• Encloses the cotton fibre -> protects the fibre• Composed of cotton wax-mixture of fats and oils.• oily film -> hard like varnish.

b. Primary wall• Built from cellulose• Cellulose molecular chain randomly arranged• 0.1-0.2 microns thick

c. Secondary wall• Also composed of cellulose

d. Lumen• Cylindrical void (i.e. space) along the length of the fibre • Occupies 30-35 % of total area of cross-section

Chemical composition of cottonChemicals Composition (%)

Cellulose(glucose molecules)

88 - 97

Protein(polypeptides & amino acids)

1 - 2

Oil and Wax(glycerides & fatty acids)

0.4 - 1.5

Pectins(Ca/Mg/Fe + pectic acid)

0.4 - 1.5

Minerals(chlorides/carbonates/sulphates of

K, Ca and Mg)

0.7 - 1.6

Others 0.5 - 8.0

Cellulose• Basic unit of cellulose is anhydro D-glucose • Glucose is a monosaccharide containing 6

carbon atoms – 5 in the ring and 1 in side chain

LIFE CYCLE OF SILK WORMEgg (hatches in 8-10

days)

Caterpillar (5 mg / 2-3 mm )

After 20-30 days2-5 gm / 5-9 cm

Seeks for secretion of filament / transferred to special trays

Turns into a pupa

PRODUCTION OF SILK

Drying •To kill the pupa inside the cocoon – sunlight/heating.•Process also called stifling.• Cocoons are then stored.

Sorting •Good cocoons are sorted from bad ones like stained, irregular, flossy and thin end cocoons. • colour, shape, weight, filament length, filament diameter.

Cooking • cooked or softened in hot water• to swell and soften the sericin

Reeling • continuous silk filament is extracted from the cocoons without any break and reeled using a reeling machine.

MORPHOLOGICAL STRUCTURE OF SILK

Brin

CHEMICAL COMPOSITION

• Composed of,– FIBROIN (the silk filament), and – SERICIN (the gummy substance that holds the

filaments together)

Component Mulberry Silk

Tassar silk Muga silk Eri Silk

Fibroin 70-80 % 80-90 % 80-90 % 80-90 %

Sericin 20-30 % 8-10 % 8-10 % 4-5 %

Other 2-3 % 3-5 % 3-5 % 3-5 %

• FIBROIN and SERICIN contain amino acids

Primary structure of FIBROIN (Gly-Ser-Gly-Ala-Gly-Ala)n

• The chemical composition of SERICIN is C30H40N10O16.

Gly – GlycineAla – AlanineSer - Serine

WOOL

• Wool is the oldest and the important animal fibre.

• Major production: UK, Russia, Argentina, USA• The main physical features of the wool fibre

are its length and diameter.

GRADING OF WOOLType of Wool Fibre Length Fibre diameter

Fine 3.2 – 10 cm 10 - 30 micron

Medium 5 – 20 cm 20 - 40 micron

Long 12.5 – 35.5 cm 35 - 50 micron

Cross Bred 7.5 – 15.5 cm 20 - 40 micron

Mixed Mixed length 20 - 100 micron

Wool sorting is the process of separating the wool fibres based on its quality such as length (short or long), fineness (fine or coarse), handle (stiff or soft), etc.

MORPHOLOGICAL STRUCTURE OF WOOL

• 3 structural parts:a. Epidermis or cuticleb. Cortexc. Medulla

Chemical composition of WoolComposition Percentage (%)

KeratinGrease

MoistureSuint

Sand and dirtVegetable matter

45-75 5-15

10-122-124-300-5

• Keratin:– Composed of C (~53%), H (7 %), N (18%), O (25%) and S– S content varies largely among different types of wool.– Polypeptide composed of 15-20 amino acids

• Grease:– Insoluble in water– Ester of (high molecular weight) fatty acids and

monohydric alcohol (eg. Cholesterol)• Suint:– Water soluble– K salts of fatty acids and organic amino acids

• Sand and Dirt

Protein molecule:

Dipeptide

Polypeptide

Helps to differentiate the amino acid

Polypeptide chain can be:– Straight chain but in a zig-zag form– Folded chain (arranged forward and backward on

one plane)– Coiled chain (spiral form)

FLAX

- Bast fibre- The plant grows 170 cm in height and 1.5 cm

in diameter.- On maturity, changes from green to yellow.- Better to harvest when the seed pods have

ripened.- Dried for a week – stem is collected.

PROCESSING OF FLAX Hackling •The stems are beaten against iron spikes to remove the impurities like leaves and small branches.

Retting* •Dew retting – 10-20 days•Stagnant water retting – 30-40 days•Running water retting – 20-30 days•Chemical retting – oxalic acid for 4-8 hrs

Drying and Storing •Drying makes the fibre stronger•Woody material of the stem can be removed by hackling.

*Retting is the process of separating the fibre bundles from gummy substance surrounding it.

FLAX FIBRE - LINEN

• Strongest natural fibre – 80-90% crystalline region.• High crystallinity -> dry strength and wet strength are

the same.• Length – 90-125cm• Diameter – 14-25 microns• Cross-section - Round to polygonal with a small lumen.• Moisture regain – 12%• Used for home textiles, sheeting, canvas, threads,

twines, paper making, etc.