A study on structural properties of textile fibers

Introduction:

In beginning of textile industry in all over the world, the textile fibers are essentially needed for making any textile product. So all textile fibers have to fill some required properties for proper processing. If we want to explain about the structural properties textile fibers, at first we need to know about the textile fiber.

Textile fiber :

Textile fiber has some characteristics which differ between fiber to textile fiber. Textile fiber can be spun into a yarn or made into a fabric by various methods including weaving, knitting, braiding, felting, and twisting. The essential requirements for fibers to be spun into yarn include a length of at least 5 millimeters, flexibility, cohesiveness, and sufficient strength. Other important properties include elasticity, fineness, uniformity, durability, and luster.

So we can say that all textile fibers have need a specific structure and also need some special properties.

The structure offibers refers to longitudinal and cross sectional structure and appearance of fiber. Two main reasons show the importance of microstructure of a textile fiber and filament, those are listed below:

1. Conclusive identification.

2. Influence on skin contact comfort.

The  effect of  those two reasons are shortly denoted here,

For cotton, flax, viscose or wool it is possible to make a conclusive identification by microscopic examination of the longitudinal and cross-sectional structure of the fiber or filament. The individual characteristics of the textile micro-structure influences skin contact comfort. For example, the minute surface irregularities of the other-wise regular and even fiber structure of cotton and silk make them comfortable and pleasant to wear. In contrast, the extremely smooth, even, regular surface structure of fibers such as nylon and polyester results aesthetically un-desirable and uncomfortable against the skin.

In this part now I’m giving a short brief about some specific properties of textile fibers which are mandatory for any

Physical Properties:

1. Length

2. Fineness

3. Crimp

4. Maturity

5. Lusture                        

6. Softness

7. Resiliency

8. Work of rupture

9. Density

10. Appearance

11. Flexibility

12. Toughness

13. Elongation

Mechanical Properties:

1. Tensile Properties.
Tensile properties indicates how a material will react to the forces being applied in Tension. Fibers usually experience tensile loads whether they are used for apparel or technical structures. Their form, which is long and fine, makes them some of the strongest materials available as well as very flexible. This book provides a concise and authoritative overview of tensile behaviour of a wide range of both natural and synthetic fibres used both in textiles and high performance materials.

2. Flexural Properties.
Flexural properties is one of the mechanical properties of textile material. It is the property or behaviour shown by the fibre or material when we bend it. The importance of Flexural properties is required when we wear cloth. The flexural test measures the force required to bend a beam under three point loading conditions. The data is often used to select materials for parts that will support loads without flexing. Flexural modulus is used as an indication of a material’s stiffness when flexed.

 3 . Torsional Properties.
The behaviors which are shown by a textile material when it is subjected to a torsional force is called torsional property. It is the property of fibre or material when a Torsional force is applied on it. Here Torsional force is a twisting force that is applied on the two ends of the material in two opposite direction.

4. Fictional Properties
Frictional properties is due to the friction between the fibres. This properties are shown during processing. Too high friction and too low friction is not good for yarn. Therefore it is an important property when yarn manufacturing and processing.

Chemical properties:

Resistance to chemicals determines the appropriateness of care procedures and end uses for fibers. Chemical properties of fiber are directly related by the ratio of amorphous to crystalline regions in its polymer system. More crystalline or highly oriented polymer system will be more chemically resistant than fiber with a more amorphous polymer system. The more amorphous polymer system, with its greater inter-polymer spaces, allows penetration of the ions, molecules or radicals of degrading agent or dyes to color the fiber.

Thermal properties:

Textile fiber or filament at particular temperature gets softened and begins to melt. This temperature is a relative measure of the heat resistance of fiber. It gives the information that at what temperature the fiber may be safely heat-processed during finishing, pressed during garment manufacture, hot laundered, and ironed after dry cleaning.The softening and melting point temperatures of a fiber are directly related to the crystallinty of its polymer system, the length of its polymers, and the type and number of inter-polymer forces of attraction holding its polymer system together. Due to more crystalline polymer system, there will be longer polymer chain and stronger will be its inter-polymer forces of attraction. Thus more heat or kinetic energy will be required to free the polymers from each other. This would result in the fiber having a greater resistance to heat, as well as to softening and melting at a higher temperature.

Fiber tenacity

Tenacity, or tensile strength, is the ability of a textile to withstand a pulling force. The tenacity is measured by measuring the force needed to break or rupture the fiber when both of its ends are in clamp. Breaking tenacity for a fiber is the force, in grams per denier or tex, required to break the fiber. The tenacity of fiber differs when it is wet or when it is dry. In general it directly depends on:

a. Length of its polymers              

b. Degree of polymer orientation

c. Strength and types of inter-polymer forces of attraction formed between polymers

Thus, the longer the polymers, the more crystalline will be the orientation, as a result stronger will be the inter-polymer forces of attraction and the stronger and more inflexible be the fiber. type of processing of textile materials by these fibers.

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.

Finally the most important issue of structural properties of a fiber is fiber orientation are mentioning below:

Fiber 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:

1.  Amorphous regions (random).

2.  Crystalline regions (highly ordered, highly oriented).

Within the fiber orientation 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.

Now the properties of Amorphous and Crystalline region of fibers are listed below :

Properties of Amorphousfibers :

• More absorbent
• Weaker
• Less durable
• More easily degraded by chemicals
• More easily dyed
• More pliable, softer handling
• Plastic, more easily distorted

Properties of crystalline fibers :

• Less absorbent
• Stronger
• More durable
• Less easily degraded by chemicals
• Less easily dyed
• Less pliable, stiffer handling
• Less plastic, resist being distorted

The diagram of Amorphous and Crystalline region of a sample fiber are including below for easy understanding of fiber orientation.

Fig : A fiber’s polymer system representing amorphous and crystalline regions.

Based on this above discussion we can strongly assured that the structural properties of  fibers , specially textile fibers are very important part of textile sector because without these properties a textile fiber can not be processed for its further step.

Special Thanks to Arnab Basak Sir for his precious assistance to make this analysis successfully.

References :

                     1. www.iit.elearning.in

                     2. Handbook of textile fiber by ‘‘H.Voltz”

Md. Bakhtiar Rana

B. Sc in Textile Engineering

City University Bangladesh