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.
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