CHAPTER FOUR

LECTURE 4 ON

Man- Made Fiber Formation and Regenerated Fibers.

BAHIR DAR UNIVERSITY (EiTEX)BAHIR DAR UNIVERSITY (EiTEX)

By: Bademaw Abate(Lecturer)

INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION � Textile fibers are made by man starting from various kinds ofraw

materials. Thestarting raw materials for fiber making can benatural and

synthetic polymers.

� Accordingly man- made fibers are classified in toregenerated and

synthetic.

Basic principle in fiber manufacturingBasic principle in fiber manufacturing

� Conversion of the fiber-forming substance into a fluid solution or melting

� Extrusion of the fluid throughspinnerets

� Solidification of the extrudedfilaments

� The technology of man made fiber manufacturing --- SPINNING

� A spinneret (perforated plate) may have fromone to several hundred holes.

Monofilament: when the spinneret has only single hole

Multi-filament: the bunch of filaments from a multi-hole spinneret.

TECHNOLGY OF MAN MADE FIBERSTECHNOLGY OF MAN MADE FIBERSTECHNOLGY OF MAN MADE FIBERSTECHNOLGY OF MAN MADE FIBERS

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� Spinneret hole may be circular or some other shape based on requirement. This

enables production of filaments having differentcross-section.

SPINNING METHODSMELT SPINNING

� In melt spinning, the fiber-forming substance is melted forextrusion through

the spinneret and then directly solidified by cooling in an air stream.

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KeyKeyKeyKey requirementsrequirementsrequirementsrequirements:::: EaseEaseEaseEase ofofofof melting,melting,melting,melting, meltmeltmeltmelt stabilitystabilitystabilitystability

andandandand optimumoptimumoptimumoptimum meltmeltmeltmelt viscosityviscosityviscosityviscosity

Examples: Nylon, Polyester

Cont..

SOLUTION SPINNING

� In solution spinning the fiber forming polymer is dissolvedin a suitable solvent

for extrusion through a spinnerette.

� Themajorsolutionspinningoperationsaredry spinning andwet spinning.

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� Themajorsolutionspinningoperationsaredry spinning andwet spinning.

� In dry spinning the polymer solution is extruded into a stream of warm air, which

evaporates the volatile solvent and solidifies the filaments.

� In wet spinning the polymer solution is extruded into a bath containing chemicals,

which neutralize the solvent and coagulate (solidify) the filaments.

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KeyKeyKeyKey requirementsrequirementsrequirementsrequirements:::: PolymerPolymerPolymerPolymer ssssolubilityolubilityolubilityolubility &&&& solutionsolutionsolutionsolution viscosityviscosityviscosityviscosity

DRY SPINNINGDRY SPINNINGDRY SPINNINGDRY SPINNING WET SPINNINGWET SPINNINGWET SPINNINGWET SPINNING

Example: Viscose rayonExamples: Acetate, Acrylic

Flow chart of MMF production:

1. Manufacture of the fibre forming polymer.

2. Spinning ( extrusion through spinneret)

3. Stretching/Drawing ( improving strength and crystallinity)

4. Texturing/Crimping ( developing natural fibre properties)

5. Heat setting( made dimensionally stable)

6. Cutting: According to requirements.

REGENERATED FIBERS

� The raw materials used for the production of regenerated fibers are

natural polymers.

� Nature has done the work of preparing something that can be

converted into fiber.

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� The only involvement of man is converting this material in to a

suitable fiber.

� Most widely used regenerated fibers areviscose rayon andacetate.

VISCOSE RAYON

� The raw material for viscose rayon production iscellulose

obtained fromwood pulp.

� Viscose rayon fiber is produced bywet spinning technology.

� The firs step is preparation of aspinnable solution of cellulose

knownasviscose.knownasviscose.

� Next wet spinning is carried out which involvesextrusion through

spinnerets &coagulation.

� The coagulation bath which consistsacids and salts responsible

for neutralization and regeneration of the original cellulose as

continuous filaments.

Manufacturing Process of Viscose Rayon

� The chemical structure of viscose is comparable to cotton.

� Thecellulose molecules are muchshorter than those of cotton

� Their organization in the fiber is also different (low degree of

VISCOSE RAYON: FIBER STRUCTURE AND PROPERTY

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crystallinity)

� The fiber cross-section is serrated and longitudinally striations are

observed along the length of the fiber.

DP = 250 -350

�Thetenacity is lower than cotton and muchlower wet strength

� Theelongation at break ishigher than cotton

� Viscosewrinkles easily and hashigh moisture regain than cotton

� Low tendency of static charge build up

PARAMETER CHARCTERISTIC VALUEPARAMETER CHARCTERISTIC VALUE

Tenacity 2-3

Elongation 10 – 20%

Elastic recovery Between silk and cotton

Specific gravity 1.51

Heat Conductivity Moderate

Moisture regain 11- 13%

uses of Viscose Rayon�Rayon typically has an elevated luster quality giving it a brilliant gloss

�Mainly, Rayon fibres are used inapparel industrysuch as Aloha shirts, blouses, dresses, Jackets, Lingerie, scarves, suits, ties, hats and socks…,

� Some rayon fibres are for filling in Zippo lighters, furnishings including bedspreads, bed sheets, blankets, window covers, upholstery and slipcovers..,

� For industrial purposes such as medical surgery products, non-woven items, tire cord and some other uses like diapers, towels, feminine hygiene products..,

CELLULOSE ACETATE FIBERS

� Acetate rayon is the generic name for cellulose acetate fiber in at least 74%

of the hydroxyl groups of cellulose are acetylated.

� The raw material for the production of cellulose acetate fibers is cotton

linters/wood pulp.

� The hydroxyl groups of cellulose are replaced by acetate groups.� The hydroxyl groups of cellulose are replaced by acetate groups.

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(CH3COO -)

ACETATE FIBER MANUFACTURING

� Cotton Purification: Cotton linters are first purified to remove

impurities.

� Pretreatment: Stepping in glacial acetic acid to make reactive for

acetylation

� Acetylation: Hydroxyls (-OH) in cellulose are replaced by acetyl � Acetylation: Hydroxyls (-OH) in cellulose are replaced by acetyl

groups (CH3COO -)

� Treatment with anexcess of glacial acetic acid and acetic anhydride

� Sulphuric acid dissolved in acetic acid is added to complete

acetylation.

� All the cellulose is converted intocellulose triacetate

� The cellulose triacetate thus formed is known asPrimary Acetate15

Manufacturing Process of Cellulose Acetate

� Preparation of Dope: The blended secondary acetate is mixed three times its

weight of acetone in a closed vessel. Acetone dissolves it slowly.

� The solution of cellulose acetate in acetone is thespinning dope. Dope is

filtered, dearated and then run into feed tank.

ACETATE FIBER MANUFACTURING

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Spinning� The method of spinning used is dry sinning. The dope is extruded through the

spinneret and the acetone solvent is gradually removed by means of warm air.

� Post spinning operations as usual and as per requirement.

ACETATE FIBER: MAJOR FEATURES

� Presence of bulky side chain groups leading to limited closepacking

� Presence of hydrophobic groups lower moisture characteristics

� Low tenacity [1.4gpd (dry) and 0.9gpd (wet)]

� High elongation [30% (dry) and 40% (wet)]

� Elasticrecoverygoodat low elongation

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� Elasticrecoverygoodat low elongation

� Moderate moisture regain [6.5%]

� Moderate density [specific gravity 1.32]

� Acetate Rayon is more sensitive to heat. It begins to weaken at 93 deg C. At 175

deg C it becomes sticky and melts at 260 deg C. Like nylon and polyester it is

thermoplastic.

� Acetate rayon is soluble in acetone.

Uses of Acetate fiber

�Acetate is used in dresses, blouses, foundation

garments, lingerie, garment linings, some household

furnishings, and certain specialty fabrics.

�Triacetate is used in sportswear, tricot fabrics, and in �Triacetate is used in sportswear, tricot fabrics, and in

garments where pleats and pleat retention is

important, as well as in certain specialty fabrics.

Thank You