Matter is composed of atoms linked together by bonds of varying strength. The physical properties of the materials are determined by the arrangement of these atoms and the strength of the bonds between these atoms. An essential requirement in fiber structure is some means of ensuring continuity and strength along the length of the fiber.

1. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
FIBER PHYSICS
LESSON-1
ESSENSIAL REQUIREMENT OF FIBER FORMING
POLYMERS
PREPARED BY: BADEMAW ABATE
BAHIR DAR UNIVERSITY, EiTEX
Introduction: Requirements for fiber formation
Matter is composed of atoms linked together by bonds of varying strength. The physical
properties of the materials are determined by the arrangement of these atoms and the strength of
the bonds between these atoms. An essential requirement in fiber structure is some means of
ensuring continuity and strength along the length of the fiber. These two basic requirements are
met in the following manner:
 Long-chain molecules – provided in the form of linear polymer molecules as the building
blocks of fibers (or a sort of skeleton)
 A more or less parallel arrangement of the above long-chain molecules
 Lateral forces to hold the molecules as a stable or coherent structure (otherwise the linear
molecules will slip past one another!)
 Some measure of freedom of the long-chain molecules in order to give the necessary
extensibility to the fiber
 Some measure of openness to give room for moisture absorption and uptake of dyes.
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2. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Both natural and manmade fibers are mainly composed of the high polymer system or
macromolecules. Polymer system or macromolecules of the textile fiber must satisfy the
minimum requirements, if it is to serve as a fiber. Macromolecular structure is necessary for the
production of materials of high mechanical strength and high melting point. The natural fibers
consist of long chain molecules of linear molecular type. Further, the chain molecules are
oriented into the parallel bundles in the process of growth. Based on these investigations, it is
assumed that polymers must satisfy the minimum requirements, if it is to serve as a fiber. The
requirement for the fiber forming polymer are mentioned as follows:-
i. Hydrophilic
ii. Chemical resistant
iii. Linear
iv. High molecular mass
v. Long chain molecules
vi. Capable of being oriented and Crystallized
vii. Able to form high melting point polymer system
viii. Able to form intermolecular cohesive forces
The various polymers, which constitute the polymer systems of fibers, may or may not meet all
these requirements. However, the polymer systems of some commonly used textile fibers which
meet all the above requirements are Acetates, Acrylics, Cotton, Flax, Nylon, Polyester, Silk,
Viscose and Wool.
Man-made fibers such as the chloro-fibers, polyethylene and polypropylene fibers are restricted
in their textile use because they do not satisfactorily meet the first, sixth and seventh properties.
Natural cellulose fibers such as abaca, coir, hemp, jute, kenaf, ramie and sisal have very
restricted textile application as they are very stiff. The polymers of the natural fibers angora,
cashmere and mohair largely fulfill the above requirements, but because the fibers are expensive
because of their scarcity so they are used infrequently.
i. Hydrophilic properties
Fiber polymers should be hydrophilic. Polar nature of fiber and amorphous polymer system of a
fiber are responsible to absorb moisture.
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3. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Amorphous polymer system: Crystalline polymer system of a fiber does not allow even very
small molecules, such as water, to enter into the fiber structure. This explains the poor moisture
absorbency of all synthetic fibers which are very crystalline in nature. More the amorphous
nature of fibers, such as wool and viscose, more they are absorbent in nature.
Polar: Presence of certain chemical groups influences the moisture absorbency for example, the
hydroxyl or -OH groups of cellulose which attract water molecules.
A fiber is comfortable to wear if its polymer system is made up of hydrophilic polymers, and the
system allows the entry of water molecules. Hydrophobic polymer fibers whose polymers are
non-polar are yet used as fibers for textile applications. In order to make the textile materials of
these fibers more water attracting, absorbent and comfortable, hydrophobic-polymer fibers need
to be blended with the hydrophilic polymer fibers to get desired properties.
Examples: Hydrophobic-polymer fibers like nylon and polyester are often blended with cotton,
viscose or wool (e.g. two-thirds polyester/one-third cotton blend). Blending improves the water
absorbency and comfort of their textile materials. Acrylics are also hydrophobic polymer fibers.
Knitted outerwear made of acrylics is very popular; and it will be found that it is usual to wear
this non-absorbent knitwear over an absorbent or hydrophilic-polymer fiber garment to counter
or reduce potential discomfort which might otherwise be experienced.
The hydrophobic nature of crystalline synthetic fibers gives rise to static electricity. This can be
undesirable during yarn and fabric manufacture, as well as during garment manufacturing and
subsequent wearing of the apparel. In amorphous fibers there is the absence of static electricity,
usually due to more absorbency of moisture. It is due to this reason that the amorphous fibers are
blended with the more crystalline fibers to make the crystalline polymer system more
comfortable to wear.
A fiber consisting of hydrophilic polymers attracts water molecules which prevent or enable the
discharge of any static electricity accumulating. The static electricity is discharged by the water
molecules, because of their polarity to the surrounding atmosphere. The generation of the static
electricity on a fiber is undesirable because it will cause the fiber to attract the dirt particles more
readily and soil more quickly. This causes the fiber to cling together and creates discomfort
during wear.
ii. Chemical resistance
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4. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Fiber polymer should be chemically resistant for a reasonable period of time against the common
degrading agents such as sunlight and weather, common types of soiling, body exudations,
laundry liquors and dry cleaning solvents. Chemically resistant polymer should also not be toxic
or hazardous to wear against human skin. Fiber polymer should be chemically resistant they
should not be inert means totally unreactive. Chemical inertness of fiber polymers results in
detrimental effect on other fiber-forming requirements. The polymers of chloro-fibers,
fluorocarbon, polyethylene and polypropylene may be regarded as chemically inert from a
practical point of view.
iii. Linearity
Fiber polymer should be linear i.e. the polymers should not be branched. Highly linear polymers
will form more crystalline regions, which results in a large number of inter-polymer forces of
attraction within the polymer system.
1) Only linear polymers results in polymer alignment which brings sufficient inter-polymer
forces of attraction to give a cohesive po1ymer system and, hence, useful textile fiber.
2) In manufacturing of manmade fiber it should have the right stereo polymer for the extrusion of
textile filaments.
3) Linear polymers can assume various configurations.
4) Branched polymers prevent close packing of polymers unlike in the case of linear polymers.
Branched polymers, cross linked polymers, or three dimensionally cross linked polymer systems
are not desirable for the production of textile fibers. Polymers which are bulky or branched
cannot pack close together, which prevents the formation of crystalline regions in the polymer
system of the textile fiber. The inability to form crystalline regions means there will be less
forces of attraction exerting their influence to hold the polymers in an orderly arrangement, thus
resulting in a weak fiber.
Many fiber polymers, which need to be linear, have side groups, as distinct from branches. Side
groups causes 'bulges' along the polymer backbone, rather than the distinct projection of a
branch. Examples of fibers with the side groups are the nitrile group of acrylics, the hydroxyl and
methylol groups of the cellulose fibers, and the hydroxyl and acetyl groups of ester-cellulose
fibers.
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5. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Side groups on polymers are important as they give rise to three types of linear polymer
configurations, referred to as three types of stereo-polymers. Stereo means spatial or three-
dimensional arrangements of the side groups on the polymer backbone. In manufacturing of
man-made fiber it is important to have the right stereo-polymer for the extrusion of useful
filaments. The three types of stereo-polymers are described below:
The atactic polymer
Atactic polymer is a stereo-irregular polymer. It has its side groups arranged at random i.e. there
is no particular order, for side groups which are arranged above and below the plain of the
polymer backbone. Two-dimensionally may be represented as shown in fig 1:
Fig
1: Atactic polymer
Atactic polymers are usually not found in the case of fiber polymer systems. This is because they
do not allow close alignment or orientation of polymers for the formation of enough inter-
polymer forces of attraction.
The syndiotactic polymer
Syndiotactic polymers have their side groups arranged in a regular alternating fashion above and
below the plane of the polymer backbone. Two-dimensionally may be represented as
Fig 2: Syndiotactic polymer
Such a regular polymer structure allows close enough alignment or orientation to form enough
inter-polymer forces of attraction, giving a cohesive enough system to form a useful fiber. The
polymers of cellulose and some chloro-fibers are examples of syndiotactic polymers.
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6. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
The isotactic polymer
Isotactic polymer is also a stereo-regular polymer. But it has, all its side groups arranged on the
same side or plane of the polymer backbone. Two dimensionally this may be shown as:
Fig 3: Isotactic polymer
lsotactic polymers orient in very closely dense fashion. This permits effective formation of inter-
polymer forces of attraction to give a cohesive polymer system and, thus a useful fiber.
Polypropylene and pure acrylonitrile are isotactic polymers.
iv. Molecular Mass
The polymer mass must have a comparatively high molecular mass. The average length of its
molecular chain should be in order of 1000 Å or more.
v. Length
Fiber polymers should be long. The length of polymers is directly related to the strength of fiber
by holding the crystalline regions together. To produce a fiber with adequate strength, a polymer
length of 100 nanometers is required. Polymers of such length can be oriented easily. The
orientation of polymers give rise to sufficiently effective inter-polymer forces of attraction to
form a cohesive polymer system and, hence, a useful fiber. The longer the polymers the more
cohesive will be the polymer system and the stronger will be the fiber. For this to occur the
polymers have to be aligned or well oriented so that the maximum formation of inter-polymer
forces can take place.
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7. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
.
Fig 4: A figure shows strong fiber as it has long 'path of break' [1].
Figure 5 shows polymers of low molecular weight. Although they are well oriented, the
shortness of its ‘path of break’ tends to make it weak fiber and polymers with high molecular
weight results in long ‘path of break’ results in the strong fibers with well orientation.
Fig 5: Weak fiber as it has short ‘path of break’ [1].
vi. Orientation
Fiber polymers should be capable of being oriented. The polymers are aligned into more or less
parallel order in the direction of the longitudinal axis of the fiber or filament. The orientation of
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8. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
polymers in the polymer system of any fiber consists of two forms. The two forms of polymer
orientation are:
 amorphous regions (random)
 crystalline regions (highly ordered, highly oriented)
Within the fiber polymer system:
a) The extent of the areas of crystallinity and amorphousness varies.
b) The proportions of the areas of amorphousness and crystallinity vary considerably.
c) The proportions of the areas amorphousness and crystallinity in natural fibers vary by
nature.
d) The extent of the areas of amorphousness and crystallinity can be maintained during the
production of manmade fibers.
It is not known how the orientation of polymers occurs during the growth of natural fibers. With
man-made fibers, the operation called drawing, which stretches the extruded and coagulated
filament, causes the polymers to orient themselves longitudinally into a more or less parallel
order, resulting in the formation of crystalline regions. This greatly increases the strength of the
fiber.
Amorphous polymer orientation: Amorphous orientation of the polymer system of any fiber is
called the amorphous region. Polymers are oriented or aligned at random fashion in amorphous
region, i.e. shows no particular order of arrangement.
Crystalline polymer orientation: Crystalline orientation of polymers within the polymer system
of any fiber is called the crystalline region. In crystalline regions the polymers are oriented or
aligned longitudinally into more or less parallel order.
The polymer system of any man-made and natural fiber
(i) consists of randomly arranged amorphous and crystalline regions.
(ii) May be predominantly constituted of:
- More amorphous than crystalline regions; if this is the case then the particular fiber or filament
is more amorphous fiber or filament. or
- More crystalline than amorphous regions, if this is the case then the particular fiber or filament
is more crystalline fiber or filament.
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9. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Owing to their length, most polymers pass through several amorphous and crystalline regions.
The presence of either more or less amorphous or crystalline regions determines the specific
properties of the fiber.
f. The random orientation, of the polymers are further apart which results in:
- Formation of less effective inter-polymer forces of attraction.
- Permits easier entry of water and dye molecules as well as molecules, ions and/or radicals of
degrading agents.
- Allows the polymers to be more readily displaced when the fiber is subjected to stresses and
strains during wearing.
f. The more or less parallel orientation of the polymers are often closer together which results in:
- Formation of more effective inter-polymer forces of attraction.
- Restricts the entry of water and dye molecules as well as molecules, ions and/or radicals of
degrading agents.
- Does not allow the polymers to be displaced when the fiber is subject to stresses and strains
during wearing
2. Properties of more amorphous fibers are: more absorbent, weaker, less durable, more easily
degraded by chemicals, more easily dyed, more pliable, softer handling and plastic, more easily
distorted.
2. Properties of more crystalline fibers are: less absorbent, stronger, more durable, less easily
degraded by chemicals, less easily dyed, less pliable, stiffer handling and less plastic, resist being
distorted.
Each polymer tends to form part of several amorphous and crystalline regions, which results in
the enough cohesion of the polymer system. When several polymers are aligned or oriented in
more or less parallel order they form a crystalline region. Amorphous and crystalline regions do
not occur in any particular order, they occur random throughout the polymer system of the fiber.
The amorphous and crystalline regions constituting any fiber’s polymer system are too minute to
be seen under an optical microscope.
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10. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Fig 6: A fiber’s polymer system representing amorphous and crystalline regions [1].
Fig 7: (i) an amorphous region and (ii) crystalline orientation [1].
Note: Angular bonding exists between carbon atoms and tends to impart a zigzag configuration
to the backbone of fiber polymers. o = carbon atom • = atom of another element ∝ = hydrogen
bond
vii. Formation of high-melting-point polymer systems
The fibers must have high melting point to withstand the most extreme heat conditions. Melting
point of fiber needs to be above 225° C if it is to be useful for textile manufacture and apparel
use. The longer the polymers and the better their orientation, the more inter-polymer forces of
attraction will be formed, giving a more cohesive polymer system with a higher melting point.
More heat or kinetic energy will be required to break the inter-polymer forces of attraction and
free the polymers from each other. After increasing kinetic energy the polymers are free to move
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11. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
independently of each other. This flowing or moving of the polymers in a mass is seen and
recognized as melting of the fiber.
On applying heat, fiber may melt. Continued heating leads to ignition and burning of fiber. Heat
energy possessed by a polymer system is in the form of kinetic energy which is due to the atomic
or molecular translation, rotation or vibration. At any temperature above absolute zero (-273.15°
C = 0° Kelvin), the atoms, molecules or polymers of substance constantly vibrate or are in
constant state of excitement. On applying heat to the polymer or polymer system, this rate of
vibration or the state of excitement may get increased, or decreased by removing heat. Exposure
to a naked flame can increase the kinetic energy of a polymer system and weakening of inter-
polymer forces of attraction, which will free the polymers and result in melting of the fiber.
Further, more exposure to heat may provide much more kinetic energy as to raise the state of
excitement of the individual polymers and breaking of intra-polymer bonds. This would free
individual atoms of the polymer from each other. When this occurs, the atoms would react
immediately and violently with the oxygen of the atmosphere and causes combustion of the
fiber.
The heat resistance and heat conductivity of any fiber are directly related. Cotton or viscose
shows fiber resistance to heat also conduct heat. A fiber of poor heat resistance, such as wool or
nylon, will be a non-conductor of heat. Ability of a fiber to conduct heat means heat passing
along its polymers and through its polymer system, which depends upon the degree of polarity of
its polymers. Polar sites along the lengths of the polymers provide the necessary free electrons to
convey the heat or kinetic energy along.
viii. Intermolecular cohesive forces:
A polymer should have at least a high degree of intermolecular cohesive power. This indicates
that the molecular chains should have sufficient number of sites of attraction. In the case of
fibres, the long-chain molecules are held in place by the lateral forces supplied by the hydrogen
bonds, salt linkages between the adjacent molecules, chain entanglements and so on.
Types of bonds
As regards the bonds, broadly speaking, there are three types of bonds that are present in any
given material. They are primary bonds, weak forces and intermediate bonds. In the category of
primary bonds, we have the ionic, covalent and such similar bonds wherein the bond strength is
derived by the borrowing/lending of electrons or by the sharing of electrons between two atoms.
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12. ESSENSIAL REQUIREMENT OF FIBER FORMING POLYMERS
Invariably, these bonds are very strong and high amounts of energy is required to break them;
when we break these bonds, the nature of the substance itself undergoes very great changes.
At the other extreme, we have the weak van der Waals forces, which are very weak; but they do
effect physical properties of the material, albeit on a minor and in most practical cases, on an
insignificant scale.
In the third category of the bonds, we have the intermediate or secondary bonds which are
neither strong, nor weak. A common example of the secondary bond is the hydrogen bond that
generally forms between hydroxyl groups and such similar groups. These intermediate bonds,
particularly the hydrogen bond, are of high importance in deciding the fibre properties during
processing and usage. Hydrogen bond is formed between hydrogen of one molecule (or part of
one molecule) and oxygen (or nitrogen) of another (or part of another) molecule. The strength of
the above bond i.e., the energy to break the bond is neither too high, nor too low. The usual range
of various types of bonds is given below:
Bond strength:
 Ionic/covalent – 300 to 500 k J per mole
 van der Waals – 4 to 8 k J per mole
 Hydrogen bond – 40 k J per mole
References
E.P.G. Gohl, L.D. Vilensky, Textile science, Longman Cheshire Pty Limited, 1980
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