Natur al Fibers

7/29/2019 Natur al Fibers

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Natural Fibers

Cotton

Natural Cellulosic Fiber

Growth & Production:

Cotton plant is a member of Malvacae family. It is cultivated in warm climates both humid and dry. The cotton blossom, which appears creamy white or light yellow on first day, it changes to pink,

lavender, or red on second day.

The petals drop off after 48 hours, leaving the boll or seed pod in which the fibers form. 50-80 days later the pod bursts open and fleecy cotton fibers are ready for picking.

Processing:

Picking Ginning

It is the process where the fiber, called cotton lint (trade

name), is separated from the seed. The seeds are

valuable by-product of the cotton industry which is used

for cattle feed and cottonseed oil. The fibers or cotton

lint are packed into large bales at the gin. Each bale

weighs about 500 pounds gross.

Classification of FiberThe sample is taken from the bales for determining the

class. Factors like staple length, the grade and the character of the cotton. Staple length refers

to the length of the lint and is determined to some degree by the variety of cotton. Fiber grade

depends on color, amount of foreign matter present and ginning preparation. The color can vary

from white to gray or yellow. Cotton may be spotted or tinged, bright or dull.

YarnCotton Fiber Morphology:

A mature cotton fiber has the following six parts. The cuticle is the outer waxy layer, which

contains pectins and proteinaceous materials. It serves as a smooth, water-resistant coating, which

protects the fiber. This layer is removed from the fiber by scouring.

The primary wall is the original thin cell wall. Mainly cellulose, it is made up of a network of

fine fibrils (small strands of cellulose), which makes for a well-organized system of continuous, very fine

capillaries. It is well known that fine capillaries rob liquids from coarse capillaries. The fine surface

capillaries of each cotton fiber contribute greatly to cottons wipe-dry performance.


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The winding layer (also called the S1 layer) is the first layer of

secondary thickening. It differs in structure from both the primary wall

and the remainder of the secondary wall. It consists of fibrils aligned at 40

to 70-degree angles to the fiber axis in an open netting type of pattern.

The lumen wall (also called the S3 layer) separates thesecondary wall from the lumen and appears to be more resistant to

certain reagents than the secondary wall layers. The lumen is the hollow

canal that runs the length of the fiber. It is filled with living protoplast

during the growth period. After the fiber matures and the boll opens, the

protoplast dries up, and the lumen naturally collapses, leaving a central

void, or pore space, in each fiber.

Throughout the fiber structure, there are variously sized pores or

capillary spaces between the variously sized fibrils in each of the six fiber

parts. Thus, the cotton fiber can be viewed as a microscopic physical

sponge with a complex porous structure.

This internal structure makes cotton fibers accessible to liquids

and vapors. The capillary action of the fibrils pulls liquid in, where it is held

in pores between the fibrils. This structure accounts for cottons

wickability and unique absorbing capacity.

Chemical Structure of Cellulose:


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Fiber Properties:

Microscopic Properties:

Cotton fibers are composed of outer cuticle and primary wall, a secondary wall, and a central

core a lumen.

The cross section of the fiber shows these three layers. The contour varies some fibers are

nearly circular, some are elliptical and some are kidney-shaped. Immature fibers exhibit thin wall

structures and large lumen, while mature fibers have thick walls and small lumen.

The longitudinal view of the fiber shows a ribbon like shape with twist (convolutions) at irregular

intervals. The diameter of the fiber narrows at the tip.

Cross sectional View Longitudinal View

Thermal Properties:

Cotton burns rapidly and quickly with the smell of burning paper. It leaves a small amount of fluffy gray

ash. Long exposure to dry heat above 149C will cause the fiber to decompose gradually and

temperatures greater than 246C will result in rapid deterioration.

Chemical Properties:

Cotton is highly resistant to alkalis; they are used in finishing and processing of fiber. Most detergents

and laundry aids are alkaline, so cotton can be laundered in these solutions with no fiber damage.

Strong acids destroy cotton, and hot dilute acids will cause disintegration. Cold dilute acids cause

gradual weakening, but the process is slow and may not be immediately evident. Cotton is highly

resistant to most organic solvents and to all those used in normal care and stain removal. Prolonged

exposure to sunlight causes the cotton fiber to become yellow and will gradually result in loss of

strength.

Biological Properties:

Cotton is damaged by various microorganisms. Mildew will produce a disagreeable odor and will result

in rotting and loss of strength. Silverfish eat cotton cellulose, especially if it is sized.


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Physical Properties & Evaluation:

Property Evaluation

Shape Fairly uniform in width, 12-20 micrometers; length

varies from 1 cm to 6 cm ( to 2 inches); typical

length is 2.2 cm to 3.3 cm ( to 1 inches).Luster high

Tenacity (strength)

Dry

Wet

3.0-5.0 g/d

3.3-6.0 g/d

Resiliency low

Density 1.54-1.56 g/cm

Dimensional stability good

Moisture absorption raw:

conditioned saturation

mercerized: c

onditioned

saturation

8.5%

15-25%

8.5-10.3%

15-27%+

Resistance to acids alkali organic solvents sunlight

microorganisms insects

Damage, weaken fibers

resistant; no harmful effects

high resistance to most

Prolonged exposure weakens fibers.

Mildew and rot-producing bacteria damage fibers.

Silverfish damage fibers.

Thermal reactions to heat to flame Decomposes after prolonged exposure totemperatures of 150C or over.

Burns readily.

Applications:

Used to make highly absorbent bath towels and robes; denim, used to make blue jeans;and corduroy, seersucker, and cotton twill.

Socks, underwear, and most T-shirts are made from cotton. Cotton also is used to make yarn used in crochet and knitting. Fabric also can be made from recycled or recovered cotton that otherwise would be

thrown away during the spinning, weaving, or cutting process.

While many fabrics are made completely of cotton, some materials blend cotton withother fibers, including rayon and synthetic fibers such as polyester.

It can either be used in knitted or woven fabrics, as it can be blended with elastine tomake a stretchier thread for knitted fabrics, and things such as stretch jeans.

Bedding products, draperies and curtains, upholstery fabrics, rugs and wall coverings.


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Medical, surgical and sanitary supplies Industrial abrasives. The leaves and stalks of the cotton plant are also used for soil enrichment by plowing

them into the soil.

Safety factors associated with Cotton:

Byssinosis, also called mill fever or brown lung disease, is a pulmonary ailment, similar to

bagassosis or silicosis that is alleged to develop on repeated inhalation of cotton dust. A small

percentage of textile workers exposed to cotton dust contract byssinosis. Incidence of the disease can

be controlled with adequate regulation of dust levels in work areas.

Fiber Identification of Cotton Fiber:

Burning Test:

Fiber Approaching

Flame

In the flame Away from

Flame

Odor Residue

Cotton Does not

shrink away,

ignites on

contact

Burns quickly Continues

burning with

an after glow

Smell of

burning paper

Light, fluffy,

grey in color,

easy to crush

Chemical Test:

S.No. Experiment Observation Inference

1. Take the fiber and dip it in 30-50%

Sulphuric acid and heat

The fiber chars and

dissolves.

Cellulosic fiber, could

be cotton or rayon

2. Take the fiber and dip it in 60% sulphuric

acid solution in a test tube and leave it for

5-10 minutes at room temperature

Fiber dissolves

Fiber does not dissolve

(may disintegrate)

Rayon confirmed

Cotton confirmed

Silk

Natural Protein Fiber

Growth & Production:

Silk is produced by the larvae of several moths, but the Bombyx mori is the only one raisedunder controlled conditions.

The silkworm extrudes the liquid fiber from two tiny orifices or spinnerettes in its head. As the liquid emerges into the air, it solidifies into silk filaments. The fibers are coated with the

gummy substance called sericin.

Processing:

Reeling: Silk filaments are unwound from the cocoons in a manufacturing plant called a filature.The cocoons are placed in hot water to soften the gum, and the surfaces are brushed lightly to


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find the ends of the filaments. The ends are collected, threaded through a guide, and wound

onto a wheel called a reel, hence the name reeling.

Throwing: As the fibers are combined and pulled onto the reel, twist can be inserted to hold thefilaments together. This is called throwing, and the resulting yarn is thrown yarn.

Spinning: Short ends of silk fibers from the outer and inner edges of the cocoons and frombroken cocoons are spun into yarns in a manner similar to that used for cotton.

De-gumming: Sericin remains on the fibers during reeling and throwing. It is left on through thefabric construction process. Before finishing the gum is removed by boiling the fabric in soap

and water. The presence of gum or sericin increases the tendency for silk to water spot.

Fiber Properties:

Silk is natural protein fiber. The actual fiber protein , called fibroin is composed of about fifteen

amino acids hooked together in long molecular chains. Sericin, the gum that holds the filaments

together is also a protein substance.

Chemical Composition and Molecular structure

The protein in silk is fibroin, which contains 15 amino acids in polypeptide chains. Silk has

reactive amino (NH2) and carboxyl (COOH) groups. Silk has no cross linkages and no bulky side chains.

The molecular chains are not folded as in wool, but are almost fully extended and packed closely

together. Thus silk is highly oriented, which gives the fiber its strength. As with all fibers there are some

amorphous areas between the crystalline areas, giving silk its elasticity.

Microscopic Properties

Longitudinal View: Cultivated de-gummed silk resembles a smooth, transparent rod. If gum is

still present fiber surfaces are rough and irregular. Wild silk tends to be uneven and darker. It may have

longitudinal striations.

Cross-sectional View: It shows triangular fibers with no markings. Two filaments usually lie with

their flat sides together. This can be explained by the fact that two filaments are extruded

simultaneously by each silkworm. The two filaments are called brins.


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Thermal Properties

Silk will burn directly in the path of flame. After removal from flame it sputter and eventually

extinguish itself. It leaves a crisp, brittle ash and gives off an odor like that of burning hair or feathers. It

scotches easily if ironed with temperatures above 149C and white silk will turn yellow if pressed with a

hot iron.

Chemical Properties

Silk is damaged by strong alkalies and will dissolve in heated caustic soda. Weak alkalies such as

soap, borax, and ammonia cause little damage to silk unless they remain in contact with the fabric for a

long time. While mineral acids can dissolve silk and cause contraction and shrinkage, organic acids do

not damage and are used in finishing processes. Rustling and crunching sound is developed by exposure

to organic acids.

Cleaning solvents and spot removing agents do not damage silk, but chlorine bleaches cause

fiber disintegration. Hydrogen peroxide and perborate bleaches can be used safely.

Sunlight tends to accelerate the breakdown of silk.

Silk is poor conductor of electricity, which results in the buildup of static charges. Like other

protein fibers it has lower thermal or heat conductivity than cellulosic fibers.

Physical Properties

Shape and appearance Fine and long, usually measures 1000 to 1300

yards and can be as long as 3000 yards.

Width: 9 to 11 microns. Fibers are smooth, Color:

Off-white to cream.

Wild silk is uneven and is tan to light brown in

color.

Luster high, Wild silks have duller luster because of their

coarser size, less regular surface, and presence of

sericin.

Strength-gpd Dry: 2.4-5.1, wet: 2.0-4.3

Resiliency Medium

Density 1.25-1.34

Moisture absorption

20C, 65% R.H.

11

% elastic recovery 92 at 2% extension

% elongation Dry: 10-25, Wet: 33-35


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Biological Properties

Silk resists attack by mildew and most other bacteria and fungi. It is attacked by carpet beetles.

Applications:

Silk has been queen of fibers for centuries. It is used as luxury fabrics and for high fashion items.Silk offers variety of fabrics, used in sportswear; mens and womens suits, lingerie, dress, blouse

and shirt fabrics, and decorator fabrics for home and offices.

Fiber Identifying Methods:

Silk Curls away from the

flame

Burns slowly and

splutters

Self extinguish-ing Smell of burning h

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