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.
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.
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.
Fiber Properties From an Engineering Perspective
Requirements for Fiber Forming Polymers
1. Hydrophilic2. 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)
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| Crystalline and Amorphous Regions |