Essential Requirements of Fiber Forming polymer

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There are 7 essential requirements of fiber-forming polymer. In this writing, I am going to discuss all of them with you. So let's get started.

7 Requirements of Fiber Forming Polymer

  1. Hydrophilicity 
  2. Chemical resistance
  3. Linearity 
  4. High molar mass 
  5. Long-chain molecule
  6. Orientation
  7. Formation of high-melting-point polymer systems
Essential Requirements of Fiber Forming polymer

1. Hydrophilicity

The polar nature of fiber and the amorphous polymer system of fiber are responsible to absorb moisture. On the other hand, the crystalline polymer system of 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. The more the amorphous nature of fibers, such as wool and viscose, the more they are absorbent in nature.

The presence of certain chemical groups influences the moisture absorbency, for example, the hydroxyl or -OH groups of cellulose which attracts water molecules. A fiber is comfortable to wear if its polymer system is made up of hydrophilic (water-loving) 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. 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)

Why amorphous fibers are blended with crystalline fibers?

It improves the water absorbency and comfort of their textile materials. 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 static electricity on 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.

2. Chemical Resistance 

Fiber polymer should be chemically resistant for a reasonable time against the common degrading agents such as sunlight and weather, common types of soiling, body exudations, laundry liquors, and dry cleaning solvents. The 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. 

Examples

The polymers of chloro-fibers, fluorocarbon, polyethylene, and polypropylene can be regarded as chemically inert from a practical point of view.

3. Linearity 

Why are linear polymers more suitable to use as fiber-forming polymers?

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.
  • Only linear polymers result in polymer alignment which brings sufficient inter-polymer forces of attraction to give a cohesive polymer system and, hence, useful textile fiber.
  • In the manufacturing of manmade fiber, it should have the right stereo polymer (NB: Discussed in detail below) for the extrusion of textile filaments.
  • Linear polymers can assume various configurations.
  • Branched polymers prevent close packing of polymers, unlike linear polymers. 

Why are the branched polymers less suitable to use as fiber-forming polymers?

Branched polymers, cross-linked polymers, or three-dimensionally cross-linked polymer systems are not desirable for the production of textile fibers. Polymers that 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 fewer forces of attraction exerting their influence to hold the polymers in an orderly arrangement, thus resulting in a weak fiber.

Three types of stereo-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 the manufacturing of man-made fiber, it is important to have the right stereo-polymer for the extrusion of useful filaments.

a) Atactic Polymers

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 that are arranged above and below the plane of the polymer backbone. 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.

b) Syndiotactic Polymers 

Syndiotactic polymers have their side groups arranged in a regular alternating fashion above and below the plane of the polymer backbone. 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.

c) Isotactic Polymers

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. Isotactic polymers orient in a very closely dense fashion. This permits the 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.

Textile Fibers
Images from: pixabay and freepik

4. High Molar Mass

The polymer mass must have a comparatively high molecular mass. The average length of its molecular chain should be in the order of 1000 Å/100 nm or more.

5. Long-Chain Molecule

Fiber polymers should be longer. The length of polymers is directly related to the strength of the 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 gives rise to sufficiently effective inter-polymer forces of attraction to form a cohesive polymer system and, hence, a useful fiber. So we can say that
  • the longer the polymers, 
  • the more cohesive will be the polymer system 
  • and the stronger will be the fiber.

6. 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 polymers in the polymer system of any fiber consists of two forms. The two forms of polymer orientation are:
  • Amorphous regions (randomly oriented) 
  • Crystalline regions (highly ordered, highly oriented)

 Properties of more amorphous fibers are

  • More absorbent
  • Less durable
  • More easily degraded by chemicals
  • More easily dyed
  • More pliable
  • Softer and plastic
  • More easily distorted
 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 or radicals of degrading agents.
  • Allows the polymers to be more readily displaced when the fiber is subjected to stresses and strains during wearing.

 Properties of more crystalline fibers are

  • less absorbent
  • More strong and more durable
  • less easily degraded by chemicals
  • less easily dyed
  • less pliable
  • stiffer handling and less plastic,
  • resist being distorted.
 The parallel orientation of the polymers are often packed 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 or radicals of degrading agents.
  • Does not allow the polymers to be displaced when the fiber is subject to stresses and strains during wearing.
Each polymer tends to form part of several amorphous and crystalline regions, which results in 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 randomly 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.


7. Formation of High Melting Point Polymer Systems

  • The fibers must have a high melting point to withstand the most extreme heat conditions.
  • The 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 independently of each other.

Source

  1. Advanced Polymer Chemistry (Dr. Shekh Md. Mamun Kabir)
  2. The Elements of PSE (Alfred Rudin)
  3. Polymer Science (V R Gowariker, N V Viswanathan and Jayadev Sreedhar)
  4. Textbook of Polymer Science (Fred W. Billmeyer, Jr.)
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