Synthetic fiber and its production process Introduction:

Textile industry is one of the few basic industries, which is characterized as a necessary

component of human life. One may classify it as a more glamorous industry, but whatever it is, it

provides with the basic requirement called clothes. There are numerous kinds of fibers and other raw

materials, which are used to produce a cloth. This paper provides an insight about the basics of some

synthetic fibers, its production process and the terms that are used all around the world in context of

textile industry.

Textile and Clothing (T&C) is one of the largest and oldest industries present globally. The T&C

industry provides jobs with no required special skills, which in turn plays a major role in providing

employment in countries like Bangladesh, Vietnam, Sri Lanka and Mauritius. Therefore, it plays a

vital role in the increase of Gross Domestic Product (GDP) value of these countries. The textile

industry is classified into three main categories: cellulose fibers (cotton, rayon, linen, ramie, hemp

and lyocell), protein fibers (wool, angora, mohair, cashmere and silk) and synthetic fibers (polyester,

nylon, spandex, acetate, acrylic, ingeo and polypropylene).

Conditions

Terms that makes a fiber useful for production and industrial use as a textile material in given

below:

Raw materials must be available or producible in sufficient quantities and for reasonable

prices.

Existing methods must allow processing of these raw materials to polymers and then to

filaments or fibers without high cost or damage to the environment.

The intermediate and final products must have sufficient continuity in terms of quality and

quantity.

The final price of the yarn made from the fibers or filaments must be bearable for the market.

The fiber has to be either endless and possibly capable of being textured or must be capable

of being processed in a mechanical spinning process, and must fulfill the following

requirements:

The resulting yarn has to show sufficient tenacity and elasticity, and the initial elastic

modulus may not be too low.

For textile applications the staple length should not be too low and somewhat uniform

or within a desired distribution. For paper like product, reinforcements, and flock

fibers, uniform staple lengths are required..

The fibers have to provide a certain degree of friction among each other.

Flexibility and elasticity are relevant for the mechanical spinning and subsequent

processes.

The fiber determines the lowest titer of the yarn as well as the hand, breathability,

comfort etc.

Raw materials for Synthetic Fibers

The following information shows most of the presently used fiber materials that can be used and

categorized as following:

Fibers from synthetic polymer

Polymerization fibers: 1) Polyethylene. 2) Polypropylene. 3) Polyacrylonitrile. 4)

Modacrylic. 5) Polyvinylchoride. 6) Polyfluoride. 7) Vinylal. 8) Trivinyl. 9)

Elastodien

Polycondensation fibers: 1) Polyamide (3-12), 46, 66, 610. 2) Polyester. 3)PET.

4)PBT 5) Quiana. 6)Polyurea. 7)PEEK. 8) Aromatic polyamides with meta and pera

structure.

Polyaddition fibers: 1) Polyurethane. 2) Elastan (spandex)

Chemical fibers

Viscose rayon, Hydrate cellulose, Cupro, Modal(CMD), Acetate(cellulose acetate),

Triacetate, Protein fiber(Casin), PROT (only protein), Metal alginate(ALG)

Inorganic fibers

Glass fiber, Basalt, Metal fiber, Carbon fiber

Producing the primary Materials

In order to manufacture man-made fibres, viscous, stringy liquids are needed. The matter that results

from dissolving or heating (e.g. from a substance in granular form) is called the spin mass.

Today, three manufacturing processes are primarily used to obtain spinnable material:

POLYMERISATION, POLYCONDENSATION and POLYADDITION.

POLYMERISATION

This way of joining macromolecules is only possible with single molecules which have a

double bond between two carbon atoms (CH2=CH2). But these alone cannot create an

interconnecting molecular bond. To do this they need the support of substances which are known as

catalysts. These catalysts initiate the interconnection process by ensuring that the double bond

between the two carbon atoms opens up to create a single bond -CH2-CH2-. The open single bond

stimulates another carbon double bond to open and so on. The -CH2-CH2-groups link up and a

macromolecule is formed. This process continues until it is stopped by the chemist. He achieves this

by introducing molecules which have no intention of encouraging further interlinking of the

molecules. By this he can determine the length of the macromolecule and thereby the specific fibre

properties. This is how “customised“ fibres are created. Schematically, polymerization can be

illustrated as follows:

Many identical small reactive molecules line up in a large long-chain molecule, or macromolecule.

Depending on the polymerisation process, fibres, e.g. polyamide 6 (PA 6), acrylic (PAN),

polyvinylchloride (CFL) and polypropylene (PP) fibres are produced.

POLYCONDENSATION:

This is a linking of low molecular compounds while simultaneously splitting off byproducts,

e.g. water, alcohol etc. The relation of the raw materials to each other determines the average

molecular weight. In this process, only those single molecules can be formed that have reactive

atomic groups on both ends capable of reacting with other atomic groups (molecules with

bifunctional groups). If the linking molecules are different, for example the one containing an

alcohol group and the other an acid group (e.g. a carboxylic acid group), the result is an ester.

Normally water molecules split off in the process. Illustrated schematically:

Two different types of molecules link up and produce a by-product (mostly water). This process

applies, for example, to polyester (PES) and polyamide 6.6 (PA 6.6).

POLYADDITION

Polyaddition is the linking of low molecular polyfunctional compounds. The stoichiometric

relation of the reaction elements and the chemo-physical equilibrium determines the chain length. In

this process, two different types of single molecules link up to form a macromolecule. Instead of

splitting off by-products, an alternating dislocation of the hydrogen molecules takes place. Illustrated

schematically:

This is how, for example, Polyurethane is made.

Spinning methods

In order to produce filaments (endless yarns) from the spin mass, various spinning processes

are employed. The spinnable matter is pressed through the extremely small openings of a spinneret.

Upon exiting the spinneret, the filaments produced are either gathered to a filament yarn and

spooled, or joined to form tows. Spinning is done by three different methods in case of man-made

fibers.

Wet Spinning:

Examples: Acrylic, Rayon, Spandex.

Dry Spinning:

Examples: Acetate, Acrylic, Modacrylic, spandex, triacetate, vinyon.

Melt Spinning:

Examples: Nylon, Olefin, Polyester, Saran.

The spinning processes

consist of common basic

processes which can be

seen in the illustrations:

The container holding the

spin mass (1) – the spin

pump for dosing the spin

mass (2) – the spinneret

(3) – a medium in which

the filament is formed (4)

– the device used for

gathering and spooling

the filament (5).

After the filaments have been extruded and solidified, they are drawn out between rollers

having different speeds. Drawing can also be a separate process. Spinneret size, plus spinning and

drawing conditions, determine the final filament diameter. The filaments can be combined into a tow

and then chopped into staple fibers. Man-made fibers may be spun into yarns, either alone or as

blends with other fibers.

Wet Spinning Dry Spinning Melt Spinning

Production Line Schematic Diagram

Polyester

1. crude oil

2. dimethyl-

terephthalate/

terephthalonic acid

3. glycol

4. polyethylene

terephthalate

5. melt

6. production of

polyester filament

yarn, one-step

7. production of

polyester filament

yarn, multi-step

8. production of

polyester staple

fibres

9. melt spinning

10. drawing

11. flat polyester

filament yarn

12. spinning bobbin

13. tow

14. drawing

15. crimping

16. polyester tow

17. polyester staple

fibres

Fig: Flow-chart of Polyester production line from raw material to final product

Polyamide

1. crude oil

2. aromatics

3. production of

polyamide 6.6

4. production of

polyamide 6

5. adipic acid

6. hexamethylene

diamine

7. caprolactam

8. polyamide 6 or

polyamide 6.6

polymer

9. melt

10. production of

polyamide filament

yarn, one-step

11. production of

polyamide filament

yarn, multi-step

12. production of

polyamide staple

fibers

13. melt spinning

14. drawing

15. flat polyamide

filament yarn

16. spinning bobbin

17. tow

18. drawing

19. crimping

20. polyamide tow

21. polyamide staple

fibers

Fig: Flow-chart of Polyamide production line from raw material to final

product

Viscose

1. cellulose extracted

from wood ➔

cellulose

2. alkalise

(chopping,immers

e, press)

3. preripening

4. dissolve

5. filter

6. ripening

7. spinning solution

8. production of

viscose filament

yarn

9. production of

viscose staple

fibres

10. wet spinning

11. wash/desulphuriza

tion

12. bleach/brighten

13. dry

14. viscose filament

yarn

15. drawing

16. cutting

17. washing/after-

treatment

18. drying

19. viscose staple

fibres

Fig: Flow-chart of Viscose production line from raw material to final product

Acrylic

1. crude oil

2. propylene

3. acrylonitrile

4. polyacrylonitri

le

5. spinning

solution

6. dry spinning

7. wet spinning

8. acrylic tow

9. drawing

10. washing

11. drying

12. crimping

13. acrylic tow

14. acrylic staple

fibres

15. washing

16. drying

17. drawing

Fig: Flow-chart of Acrylic production line from raw material to final product

In the melt, the chain molecules have almost no orientation. When they cool during the spinning

process they become a little pre-oriented. For solution spun fibers, e.g. hydrate cellulose, this pre-

orientation can already be increased during the coagulation in the spin bath. Melt spun fibers,

however, require a specific draw process- either in a continuous process after cooling under the glass

transaction temperature, or in a second separate process at a suited temperature. This drawing and

orienting change the tenacity and elongation of the fibers considerably: For viscose rayon for

example the tenacity increases from 1.5 to about 6.3 g/dtex with a reduction in breaking elongation

from about 30% to about 10%. The tenacity of PA can be arranged by drawing between values of 3

and 10 g/dtex with an elongation between 40% and 10%. Likewise this can be done with other

synthetic fibers. Only filaments from liquid crystal are wound during melt spinning in a fully

oriented state. Thus the fiber producer can vary orientation, tenacity and elongation depending on the

material and process.

Some Important Terms

Drawing

After spinning the man-made fibres, the parallel alignment of the molecules is not yet

optimal. Man-made fibres have to be drawn in order to acquire ultimate properties for the yarns.

Upon being drawn, a crucial event takes place inside the filaments: the chain molecules align

themselves in the longitudinal direction of the filament. The chains align themselves parallel to each

other. The cross-forces between the chains improve the tenacity. The filaments become stronger. The

extent to which they are drawn depends on their intended use.

The Spinneret

The spin mass is pressed through the so-called spinnerets. Depending on the number of holes

in the spinneret or strainer, the corresponding number of filaments is produced. If the spinneret has

only one hole, one mono-filament is spun. Spinnerets with many openings produce multifilament

yarns endlessly. Joining a large number of filaments (several ten thousand) produces a tow.

Texturing

Texturing is a procedure used to increase the volume and the elasticity of a filament yarn.

When textured, flat filaments acquire volume and bulk property. The texturing process can be carried

out separately subsequent to the drawing process. Sometimes, however, the drawing process is

carried out in a single step together with texturing on the texturing machine (draw-texturing). All

yarns which can be shaped by heat are suitable for texturing. These are predominantly polyamide and

polyester yarns. The most important texturing processes are FALSE-TWIST TEXTURING,

STUFFER-BOX TEXTURING and AIR-JET TEXTURING.

The Tow

While during the production of filament yarns each single filament bundle exiting the

spinnerets is wound onto a spool, in the production of staple fibres numerous filament bundles are

first combined to form a thick filament tow which can be crimped and cut into staple fibres.

Heat setting

In the yarn, the molecules are more or less aligned in the direction of the yarn axis. Upon

weaving and knitting, the straight yarn is mechanically forced into an arched form. The chain

molecules, however, want to bend back into a straight line, i.e. the stitches or folds are unstable. If

the yarns are heated, the macromolecules can enter into new anchoring and retain this shape upon

cooling. During heat-setting, weaved and knitted materials manufactured from synthetic fibres

become form-stable. They do not shrink and do not change in shape even upon washing.

Description of some Synthetic fiber

POLYESTER It is the most important synthetic fiber. They contain at least 85% of polymeric ester of a

substituted aromatic carboxylic acid, but not restricted to, terephthalic acid and f-hydroxy-benzoic

acid. The manufacturing process uses melt-spinning so the size and shape can be adjusted for

specific applications.

Application: It is utilized in all types of clothing, home furnishings, and as a reinforcing fiber

in tires, belts, and hoses. New insulating polyester fiberfill is used in high-performance

outdoor wear.

Polymerization Method: Bulk / Polycondensation

Monomer: Terephthalic acid or ethylene glycol

Catalyst: Antimony oxides and derivatives

Advantages: It's versatile and has low raw material and production costs. Polyester is

resistant to abrasion, has the ability to spring back into shape, does not absorb water,

and dries quickly.

Disadvantages: This includes melting when exposed to high heat and it absorbs oils and

grease making it difficult to clean. It does attract static electricity.

ACRYLIC

These fibers are unique among synthetic fibers because they have an uneven surface. The

fibers are formed by additional polymerization of at least 85% by weight of acrylonitrile.

Application: Acrylic fibers can be artificial wool because it has the warmth and softness of

wool but does not absorb water. It is often used as cold weather fiber for blankets and

sweaters.

Polymerization Method: Solution, suspension, emulsion

Monomer: Acrylonitrile

Catalyst: Organic peroxide, azo-compound, Inorganic redox initiators

Solvent: Dimethylacetamide or aqueous inorganic salt solution

Advantages: They have a high resistance to chemical and biological degradation as well as

degradation from sunlight. Acrylic is lightweight and strong.

Disadvantages: High heat can melt the fabric.

NYLON It is an artificial fiber made of polyamide which contains carbon, oxygen, nitrogen, and

hydrogen. The material is also resistant to wrinkling, does not absorb water, and it dries quickly.

Application: Nylon can be used in carpet. High-filament nylon yarns are often blended with

spandex and used in athletic apparel, swimwear, and hosiery.

Polymerization Method: bulk, Polycondensation

Monomer: Caprolactam, hexamethylene

Catalyst: Water

Advantages: The fiber is durable, strong, resists stains, hides soil, resists mildew and bacteria,

prevents static, and is resistant to abrasion.

Disadvantages: the fabric melts when exposed to high heat, can be uncomfortable to wear

next to skin, and absorbs oil and grease.

Conclusion

The chemists and technicians who specialize in man-made fibres today are capable of

manufacturing customized fibres or developing completely new substances which match the

demands posed by the different applications to a very high extent.

Customized fibres can be created specifically for use in apparel, for home furnishings or for

industrial uses. The manufacturers of man-made fibres today are able, for example, to:

– Vary the fineness of filament yarns, the number of filaments and staple fibres;

– Determine the length of fibres depending on the application and mixture;

– Produce anything from a brilliant sheen to an ultra-dull look;

– Produce the cross-sections of the filaments in a round shape, in three, six, eight-sided or any other

form;

– Alter the affinity for dyes of various classes;

– Determine the structure of yarns, be they flat, or textured or bulked yarns produced in various

manufacturing processes.

The large market share of man-made fibres underscores the advantages of man-

made fibres in processing and usage. The textile market is no longer thinkable without

man-made fibres.