Requirements of Fiber Forming Polymers

Introduction

There are several primary properties necessary for a polymeric material to make an adequate fiber. They are 1. Fiber length to width ratio, 2. Fiber uniformity, 3. Fiber strength and flexibility, 4. Fiber extensibility and 5. Fiber cohesiveness.

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Primary Properties

1. Fiber length to width ratio: Fibrous materials must have a sufficient length so that they can be made into twisted yarns. In addition, the width of the fiber (the diameter of the cross-section) must be much less than the overall length of the fiber, and usually, the fiber diameter should be 1/100 of the length of the fiber.

2. Fiber uniformity: Fibers are suitable for processing into yarns and fabrics must be fairly uniform and size. Without sufficient uniformity of dimensions and properties, the actual formation of the yarn may be impossible and unsuitable for textile usage.

3. Fiber strength: A fabric or yarn made from the fiber must possess sufficient strength to be processed into a textile fabric or other textile article. The resulting textile material must have sufficient strength to provide adequate durability during end-use.

The strength of a fabric is the ability to resist strains and stresses. It is expressed as tensile strength ex: the force per unit cross-sectional area or as tenacity, the force per unit linear density (measured in grams per denier or newton per Tex). Some fibers gain strength when wet, but soon lose strength, and some are unaffected by water.

4. Fiber flexibility: A fiber must be sufficiently flexible to go through repeated bending without significant strength deterioration or breakage of the fiber. Pliability or flexibility is the ease of bending or shaping. Flexible fibers are easily twisted to make yarns. Stiffness or rigidity is the opposite of flexibility. It is the resistance to bending or creasing.

5. Fiber extensibility and elasticity: Elasticity means the ability of a stretched material to return immediately to its original size. An individual fiber must be able to undergo slight extensions in length (less than 5%) without breakage of the fiber. At the same time, the fiber must be able to almost completely recover following slight fiber deformation. In other words, the fiber must be nearly elastic. Plasticity is the property of a fiber that enables the user to shape it semi-permanently by moisture, heat, and pressure or by heat and pressure.

6. Fiber cohesiveness: Cohesiveness is the ability of fibers to cling together. Fibers must be capable of adhering to one another when spun into yarn. The cohesiveness of the fiber may be due to the shape and control of the individual fibers of the nature of the surface of the fibers.

Secondary Properties

1. Moisture absorption and desorption: Most fibers tend to absorb moisture (water, vapor) when in contact with the atmosphere. The amount of water absorbed by the textile fiber will depend on the chemical and physical structure and properties of the fiber, as well as the temperature and humidity of the surroundings. The percentage absorption of water vapor by a fiber is often expressed as its moisture regain, which is the percentage of moisture that a bone-dry fiber will absorb from the air under standard conditions of temperature and humidity.

2. Crimp: Crimp refers to the waves or bends that occur along the length of a fiber. Wool has a natural crimp. Manmade fibers may be given a permanent crimp. Fiber crimp increases cohesiveness, resiliency, and resistance to abrasion.

3. Fiber resiliency and abrasion resistance: Resiliency is the ability of a fiber or fabric to recover, over a period of time, from deformation such as stretching, compressing, bending, or twisting. Abrasion resistance is the ability of a fiber to withstand the rubbing or abrasion it gets in everyday use.

4. Luster: Luster refers to the degree of light that is reflected from the surface of a fiber or the degree of gloss or sheen that the fiber possesses. The inherent chemical and physical structure and shape of the fiber can affect the relative luster of the fiber. Luster is the shine, sheen, or brightness of a fiber caused by the reflection of light. Smooth fibers reflect more light than rough or serrated fibers, and round fibers reflect more light than flat fibers. Man-made fibers can vary in luster from bright to dull depending on the amount of delusterant added to the solution from which the fiber is spun.

5. Density: Density and specific gravity are measured by the weight of fiber. Density is the weight in grams per cubic centimeter. Specific gravity is the ratio of the mass of the fiber to the mass of an equal volume of water at 4℃. The weight of a fabric is determined by the density of the specific gravity of the fibers.

6. Chemical resistance: A textile fiber to be useful must have reasonable resistance to chemicals as it comes in contact with its environment during use and maintenance. The chemical reactivity of each fiber depends on the arrangement of the elements in the molecule and the reactive groups it contains. Dry-cleaning solvents, perspiration, soap, synthetic detergents, bleaches, and sunshine may all cause chemical degradation on some or all of the fibers.

7. Resistance to moths and mildew: The resistance is due to the chemical composition of the fiber. A textile fiber should be resistant to attack by microorganisms and other biological agents. Many fibers undergo light-induced reactions and fibers from natural sources are susceptible to biological attack, but such deficiencies can be minimized by treatment with appropriate finishes.

8. Thermal and flammability characteristics: Fibers used in textiles must be resistant to wet and dry heat, must not ignite readily when coming in contact with a flame, and ideally should self-extinguish when the flame is removed. Flammability or inflammability refers to the ease of ignition and the speed and length of burning. Heat or thermal stability is particularly important to the fiber during the dyeing and finishing of the textile and during cleaning and general maintenance by the consumer.

Fiber Properties From an Engineering Perspective

1. A melting and /or decomposition point above 220℃.

2. A tensile strength of 5 g/denier or greater.

3. Elongation at break above 10% with reversible elongation up to 5% strain.

4. A moisture absorptivity of 2%- 5% moisture uptake.

5. Combined moisture regain and air entrapment capability.

6. High abrasion resistance.

7. Resistance to attack, swelling, or solution in solvents, acids, and bases.

8. Self- extinguishing when removed from a flame.

Requirements for Fiber Forming Polymers

1. Hydrophilic
2. Chemically resistant
3. Linear
4. Long
5. Capable of being oriented
6. Able to form high melting point polymer systems.

Crystallinity (Polymer Orientation in the Polymer System of Fibers)

Fiber polymer should be capable of being oriented. This means that the polymers can be arranged or aligned in 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 distinct, yet integrated forms. The two forms of polymer orientation are called the amorphous and crystalline regions. The amorphous region is randomly arranged, and the crystalline region is parallelly arranged. Many properties of the fiber depend on crystallinity.

Crystalline and Amorphous Regions

Comparison Between Amorphous Fibers and Crystalline Fibers

More Amorphous Fibers	More Crystalline Fibers
More absorbent	Less absorbent
Weaker	Stronger
Less durable	More durable
More easily degraded by chemicals	Less easily degraded by chemicals
More easily dyed (dye penetrates easily)	Less easily dyed
More pliable, softer handling	Less pliable, stiffer handling

Difference Between Natural and Man-Made Fiber

Natural Fibers	Man-made Fibers
The fiber, which we get from nature, is called natural fiber. Ex: Cotton, Jute, Wool, etc.	The fiber made by synthesis or regeneration is called man-made fiber. Ex: Rayon, Nylon, Lycra etc.
The number of molecules in the polymer chain is not limited.	The number of molecules in the polymer chain is limited.
The no of molecules is controlled by nature. The length of the polymer chain cannot be controlled.	The number of molecules is controlled by man. The length of the polymer chain can be controlled.
The fabric made from natural fiber is comfortable, hygienic, and good for health.	Man-made fiber is not so comfortable; some fibers are not hygienic and not good for health.
It is expensive.	It is not expensive.
It cannot grow everywhere. We have to depend on nature.	It can be produced everywhere. For production, there is no dependence on nature.