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Properties of Textile Fibers and Their Testing Method
To become a textile fiber it should have some properties or characteristics. Because textile fibers have to be spun into a yarn or made into a fabric by interlacing, or interlooping in a variety of machines including weaving, knitting, braiding, felting, bonding, etc. So we can define textile fiber as, a fiber that has the ability to be processed into yarn which can further be woven or knitted by certain interlacing methods is termed a textile fiber. We have also published an article on classification of textile fibers; you can also read this article.
Classification of Textile fibers.
Properties of Textile Fibers and Their Testing Process
In this article I will discuss different properties/characteristics of textile fiber and in the mean time I have given different testing methods of these properties.
In this article I will discuss different properties/characteristics of textile fiber and in the mean time I have given different testing methods of these properties.
Physical Properties of Textile Fibers:
Length and length uniformity:
Length of staple fiber is one of the most important characteristics. Generally a longer average fiber length is to be preferred because it confers a number of advantages. Because its processing is comparatively easy from short length fiber. Besides, more even yarns can be produced from them because there are less fiber ends in a given length of yarn and also a higher strength yarn can be produced from them for the same level of twist.
Different Types of Fiber Length and Length Uniformity Ratio
Length and length uniformity:
Length of staple fiber is one of the most important characteristics. Generally a longer average fiber length is to be preferred because it confers a number of advantages. Because its processing is comparatively easy from short length fiber. Besides, more even yarns can be produced from them because there are less fiber ends in a given length of yarn and also a higher strength yarn can be produced from them for the same level of twist.
Different Types of Fiber Length and Length Uniformity Ratio
Moisture regain:
The amount of moisture (water) present in a textile sample is referred to either by its regain or its moisture content. These two terms are often confused with each other. Moisture regain is expressed as the percentage of water in a sample compared to its oven dry weight, also referred to as its bone dry weight. Moisture content is expressed as a percentage of the total weight of the sample. The standard test method ASTM D2495-07 is most commonly employed in the textile industry to measure the regain and moisture content. The test is a simple one and can be easily performed. A sample of fiber is collected and weighed, before being oven dried at 105°C until it maintains a constant weight. The difference between the original mass before drying and the oven dried mass is calculated as a percentage, and is denoted either as moisture content or moisture regain. Moisture regain and moisture content can be measured using the following equations.
W
R= ---------------- x 100 ------------------------------ (1)
D
W
C = ---------------- x 100 --------------------------------- (2)
D + W
Where,
R is the moisture regain
C is the moisture content
W is the weight of water
D is the oven dry weight
Trash content:
The presence of undesirable material in the fiber is considered to be trash. Other synonyms include contamination and nonlint matter. It is comprised of fragments of leaves, stalks, grasses, seeds, and dust. It also includes feathers; pieces of plastic, rugs, and cloths; foreign fibrous material other than the desired fiber (like polyester or jute in cotton); and immature fibers. The immature fibers of the same desired fiber are also considered to be trash as they are not wanted in the final product. A Shirley analyzer is used to determine trash content in the fibrous tuft. It comprises a pair of rollers for gripped feeding into a sawtooth beater, rotating at a high surface speed.
Cross-sectional shape of the fiber:
Shape affects the physical and mechanical properties of textile fiber. There are many properties which are changed by the shape of the fiber’s cross section, like flexural rigidity, fabric softness, drape, crispness, and stiffness. Different natural fibers have different types of shapes, while the shape of man-made fibers depends upon the shape of the spinneret from which they are extruded, as shown in Figure. Like silk it has a triangular cross section. Cotton fibers are kidney shaped. Wool fibers are round or oval in shape.
Fiber color:
The color of the fiber is an important aspect in regard to aesthetic sense and dye shade. Every fiber type has its particular color regarding its natural or synthetic origin. In natural fibers, cotton is found as white to yellowish in color, wool fiber has whitish to blackish color grades, silk fiber is found in a lustrous white color, and jute fiber is brown. Regenerated rayon fibers are transparent in color unless dulled by pigments. In synthetic fibers, acrylic ones are white to off-white, nylon ones are off-white, polyester ones are white, para-aramid ones are dull yellowish, and carbon ones are black. Some fibers can be decolored to introduce new colors by the dying process, while other fibers have a permanent color which can’t be removed, as in the case of Kevlar and carbon fibers.
Fiber fineness:
Fineness is one of the major aspects of fiber characteristics and explains cross-sectional thickness. A fine fiber can be used to spin fine yarns. As the linear density of yarn decreases, the number of fibers also decreases by yarn diameter. The presence or absence of a single fiber shows longitudinal unevenness and variation in diameter. The decrease of fiber diameter will increase the number of fibers in a cross section of yarn and hence better yarn evenness can be achieved.
Fiber fineness has great influence on the properties of yarn and fabric. The evenness of the yarn is improved by the use of fine fibers. In addition, fine fibers need less twist and have less stiffness than coarser fibers. The increase in fiber surface due to a decrease in fiber diameter contributes to a cohesion of fibers to achieve the same strength with less twist than coarser fibers. These characteristics contribute to the hand feel of the products developed from them.
Fiber crimp:
The waviness in a fiber is known as crimp. It is measured as the number of crimps or waves per unit length or the percentage increase in the extent of the fiber on removal of the crimp. Crimps also govern the capacity of fibers to cohere under light pressure. The bi-component structure of wool increases the crimp in it. Cotton has a low crimp. Crimp allows the scattering of light due to its wavy structure and provides a dull appearance on developed products. Synthetic fibers are lustrous in structure, which can be reduced by the introduction of crimps in them. Crimps increase the thickness and enhance the bulky aspect of products.
Mechanical Properties of Textile Fiber
Fiber strength:
Strength of any material is derived from the load it supports at break and is thus a measure of its limiting load bearing capacity. Normally strength of a textile fiber is measured in tension when the fiber is loaded along its long axis and is designated as Tensile strength.
The strength and elongation of a cotton fiber can be measured by a single fiber or by the bundle method. The bundle fiber strength can be measured using an ASTM standard test procedure that employs a fiber bundle tensile testing machine. These machines are commercially available in pendulum and inclined plane mechanisms. A fiber sample is conditioned as per the standard conditioning procedure.
Tenacity:
Tenacity is the measure of the breaking strength of a textile fiber. It is also defined as ultimate breaking strength and is the maximum force a fiber can bear without breakage. The tenacity value for individual fibers is the value of load applied at breakage. The specific stress is the ratio of load to linear density and is measured in units of g/denier, cN/tex, and MPa.
Chemical Properties of Textile Fiber
Blend ratio:
Blending is the easiest way to obtain synergistic effects of two different materials. In the textile industry the blending of a fiber is a common practice to obtain the desired functional and aesthetic properties. Blends can be identified either qualitatively or quantitatively. Furthermore, the testing methods for the identification of fibers in a blend can be technical or nontechnical.
The nontechnical tests include the feeling test or the burning test; these tests are for qualitative assessment.
Maturity ratio:
The maturity of the cotton fiber is analyzed using the ASTM standard test procedure by employing polarized light or the sodium hydroxide swelling technique. A solution of 18% concentration of sodium hydroxide is used to swell the cotton fibers by soaking them. The fibers are then laid parallel on the microscope slide and covered with glass and viewed at a magnification of 400× to distinguish between immature and mature fibers. The mature fibers swell to become almost round in cross-sectional shape. This method is not considered acceptable for commercial testing due to the poor precision of the results between different laboratories.
Chemical composition:
The chemical composition of fibers depends on their origin. Natural fibers obtained from plants are made up of cellulosic structures like cotton, jute, and hemp fibers. The fibers obtained from animals are composed of amino acids like wool and silk. Regenerated fibers have the same chemical composition as those obtained from their parent origin, like viscose rayon which is cellulosic in nature. The chemical composition of synthetic fibers is based on the nature of their raw materials and the chemical reactions that occurred.
The presence of undesirable material in the fiber is considered to be trash. Other synonyms include contamination and nonlint matter. It is comprised of fragments of leaves, stalks, grasses, seeds, and dust. It also includes feathers; pieces of plastic, rugs, and cloths; foreign fibrous material other than the desired fiber (like polyester or jute in cotton); and immature fibers. The immature fibers of the same desired fiber are also considered to be trash as they are not wanted in the final product. A Shirley analyzer is used to determine trash content in the fibrous tuft. It comprises a pair of rollers for gripped feeding into a sawtooth beater, rotating at a high surface speed.
Cross-sectional shape of the fiber:
Shape affects the physical and mechanical properties of textile fiber. There are many properties which are changed by the shape of the fiber’s cross section, like flexural rigidity, fabric softness, drape, crispness, and stiffness. Different natural fibers have different types of shapes, while the shape of man-made fibers depends upon the shape of the spinneret from which they are extruded, as shown in Figure. Like silk it has a triangular cross section. Cotton fibers are kidney shaped. Wool fibers are round or oval in shape.
 |
| Figure: Schematic illustration of different cross-sectional shapes of fibers |
The color of the fiber is an important aspect in regard to aesthetic sense and dye shade. Every fiber type has its particular color regarding its natural or synthetic origin. In natural fibers, cotton is found as white to yellowish in color, wool fiber has whitish to blackish color grades, silk fiber is found in a lustrous white color, and jute fiber is brown. Regenerated rayon fibers are transparent in color unless dulled by pigments. In synthetic fibers, acrylic ones are white to off-white, nylon ones are off-white, polyester ones are white, para-aramid ones are dull yellowish, and carbon ones are black. Some fibers can be decolored to introduce new colors by the dying process, while other fibers have a permanent color which can’t be removed, as in the case of Kevlar and carbon fibers.
Fiber fineness:
Fineness is one of the major aspects of fiber characteristics and explains cross-sectional thickness. A fine fiber can be used to spin fine yarns. As the linear density of yarn decreases, the number of fibers also decreases by yarn diameter. The presence or absence of a single fiber shows longitudinal unevenness and variation in diameter. The decrease of fiber diameter will increase the number of fibers in a cross section of yarn and hence better yarn evenness can be achieved.
Fiber fineness has great influence on the properties of yarn and fabric. The evenness of the yarn is improved by the use of fine fibers. In addition, fine fibers need less twist and have less stiffness than coarser fibers. The increase in fiber surface due to a decrease in fiber diameter contributes to a cohesion of fibers to achieve the same strength with less twist than coarser fibers. These characteristics contribute to the hand feel of the products developed from them.
Fiber crimp:
The waviness in a fiber is known as crimp. It is measured as the number of crimps or waves per unit length or the percentage increase in the extent of the fiber on removal of the crimp. Crimps also govern the capacity of fibers to cohere under light pressure. The bi-component structure of wool increases the crimp in it. Cotton has a low crimp. Crimp allows the scattering of light due to its wavy structure and provides a dull appearance on developed products. Synthetic fibers are lustrous in structure, which can be reduced by the introduction of crimps in them. Crimps increase the thickness and enhance the bulky aspect of products.
Mechanical Properties of Textile Fiber
Fiber strength:
Strength of any material is derived from the load it supports at break and is thus a measure of its limiting load bearing capacity. Normally strength of a textile fiber is measured in tension when the fiber is loaded along its long axis and is designated as Tensile strength.
The strength and elongation of a cotton fiber can be measured by a single fiber or by the bundle method. The bundle fiber strength can be measured using an ASTM standard test procedure that employs a fiber bundle tensile testing machine. These machines are commercially available in pendulum and inclined plane mechanisms. A fiber sample is conditioned as per the standard conditioning procedure.
Tenacity:
Tenacity is the measure of the breaking strength of a textile fiber. It is also defined as ultimate breaking strength and is the maximum force a fiber can bear without breakage. The tenacity value for individual fibers is the value of load applied at breakage. The specific stress is the ratio of load to linear density and is measured in units of g/denier, cN/tex, and MPa.
Chemical Properties of Textile Fiber
Blend ratio:
Blending is the easiest way to obtain synergistic effects of two different materials. In the textile industry the blending of a fiber is a common practice to obtain the desired functional and aesthetic properties. Blends can be identified either qualitatively or quantitatively. Furthermore, the testing methods for the identification of fibers in a blend can be technical or nontechnical.
The nontechnical tests include the feeling test or the burning test; these tests are for qualitative assessment.
Maturity ratio:
The maturity of the cotton fiber is analyzed using the ASTM standard test procedure by employing polarized light or the sodium hydroxide swelling technique. A solution of 18% concentration of sodium hydroxide is used to swell the cotton fibers by soaking them. The fibers are then laid parallel on the microscope slide and covered with glass and viewed at a magnification of 400× to distinguish between immature and mature fibers. The mature fibers swell to become almost round in cross-sectional shape. This method is not considered acceptable for commercial testing due to the poor precision of the results between different laboratories.
Chemical composition:
The chemical composition of fibers depends on their origin. Natural fibers obtained from plants are made up of cellulosic structures like cotton, jute, and hemp fibers. The fibers obtained from animals are composed of amino acids like wool and silk. Regenerated fibers have the same chemical composition as those obtained from their parent origin, like viscose rayon which is cellulosic in nature. The chemical composition of synthetic fibers is based on the nature of their raw materials and the chemical reactions that occurred.
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