Textiles in Shoe

In the revolution of branded footwear industry role of textiles has been very important. It played a vital role in manufacturing and functioning of shoes such as wedding shoe, running shoe, rain boots, etc, but more specifically sports shoes. A shoe can contain wide range of textile material such as nylon, rubber, membrane, latex and neoprene for its coatings and finishes
If we can look at these within the shoe can be explain with various parts of shoe such as upper (everything above the sole i.e., it is the part of the shoe that keeps the sole attached to the foot), Linings
(inner surfaces of the upper to protect the foot and enhance comfort, non-wovens and more recently combinations of hydrophilic and hydrophobic fabric layers are used),Body of the upper (abrasion-resistant fabrics and impregnated fabrics are often used in), Shoelaces and other closures (most often either braided or woven from cotton, nylon or polyester). Footbed (as top covers, most commonly laminated nylon, polypropylene, or polyester fabrics).

Polyester

Polyester/ Polyethylene terephthalate (PET) is a category of polymers which contains ester functional groups in their main chain. Polyester includes naturally occurring chemicals, such as in the cutin of plant cuticles as well as synthetic such as in the polycarbonate and polybutyrate. Polyester may be produced in numerous forms such as fibres, sheets and three dimensional shapes. (200)
Polyester fibres are man-made fibres in which the forming substance is a long chain polymer composed of at least 85% by weight of an ester of dihydric alcohol and terephthalic acid. (201)

Polyesters are the polymers in the forms of fibres having hydrocarbon backbone which contain ester linkages. Hydrolysis of polyester by acid catalysed using dilute hydrochloric acid or sulphuric acid is a reversible process. But using alkali is the usual way of hydrolysing esters. By using alkali the reactions are irreversible and products are easier to separate.

Properties of polyester fibres.
Physical Properties:
The moisture regain of polyester is 0.2 to 0.8 and specific gravity is 1.38 or 1.22 depending on the type of polyester fibres is moderate. The melting point of polyester is 250-300°C. A wide of polyester fibres properties is possible depending on the method of manufacture. Generally as the degree of stretch is increased, which yields higher crystallinity and greater molecular orientation, so are the properties e.g. tensile strength and initial Young’s modulus. Shrinkage of the fibres also varies with the mode of treatment. If relaxation of stress and stain in the oriented fibre occurs, shrinkage decreases but the initial modulus may be also reduced.

Miscellaneous Properties:
Polyester fibres exhibit good resistant to sunlight and it also resists abrasion very well. Soaps, synthetic detergents and other laundry aids do not damage it. One of the most serious faults with polyester is its oleophilic quality. It absorbs oily material easily and holds the oil tenacity.
Chemical Properties:
Effect of alkalies: Polyester fibres have good resistance to weak alkalies high temperatures. It exhibits only moderate resistance to strong alkalies at room temperature and is degraded at elevated temperatures.
Effect of acids: Weak acids, even at the boiling point, have no effect on polyester fibres unless the fibres are exposed for several days. Polyester fibres have good resistance to strong acids at room temperature. Prolonged exposure to boiling hydrochloric acid destroys the fibres, and 96% sulfuric acid and causes disintegration of the fibres.
Effect of solvents: Polyester fibres are generally resistant to organic solvents. Chemicals used in cleaning and stain removal do not damage it, but hot m-cresol destroys the fibres, and certain mixtures of phenol with trichloromethane dissolve polyester fibres. Oxidizing agents and bleachers do not damage polyester fibres.
Polyester fibres have taken the major position in textiles all over the world although they have many drawbacks e.g., (a) low moisture regain (0.4%), (b) the fibres has a tendency to accumulate static electricity, (c) the cloth made up of polyester fibres picks up more soil during wear and it also difficult to clean during washing (d) the polyester garments from pills and thus, the appearance of a garment is spoiled, (e) the polyester fibres is flammable. Thus, it has been suggested that surface modifications can have an effect on hand, thermal properties, permeability, and hydrophilicity.
Polyester fabrics have been widely accepted by consumers for their easy care properties, versatility and long life, Inspite of such acceptance, complaints concerning their hand, thermal properties and moisture absorbency have been cited
Improved moisture absorbency of polyester fibres can be achieved by introducing hydrophilic block copolymers. However, this modification can lead to problems of longer drying time, excessive wrinkling and wet cling In addition, penetration of water into the interior of the fibres has not been clearly shown to improve perceived comfort
Polyester fibres are susceptible to the action of bases depending on their ionic character. Ionizable bases like caustic soda, caustic potash and lime water only effect the outer surface of polyester filaments. Primary and secondary bases and ammonia, on the other hand, can diffuse into polyester fibre and attack in depth resulting in breaking of polyester chain molecules by amide formation
One of the surface modifications is the controlled hydrolysis of polyester. The action of strong base leads to cleavage of ester linkages on the fibre surfaces the result is the formation of terminal hydroxyl and carboxylase groups on the fibre surface. Hydrolysis is believed to increase the number of polar functional groups at the fibre surface.

Cotton Fibre Morphology

Cotton Fibre Consists of four regions

Cuticle : Very thin outer layer containing wax amd pectic material

Pectin:

1. A peculiar group of carbohydrates of very complex composition.They are usually present as C and Mg salts.In immature fibres there is relatively high amount pectins (6%).
2. In mature fibres it is relatively high amount pectins (0.9-1%).
3. Decrease in pectin content with parallel increase in cellulose content proves that pectin is the parent substance from which cellulosic is formed
4. Function is to protect the fibre from atmospheric oxidation


Primary wall:

1. Composed of cellulose, Pectic and fatty matter
2. Formed in the first phase of growth
3. Cellulose fibrils are disposed transversely or circularly to produce high peripheral strength and also makes it weaker in length wise direction of the fibre and account for the low strength of immature fibre
4. In all native-cellulose fibres, the molecules are highly oriented parallel to one another, but they spiral round the fibre, thus reducing the degree of orientation parallel to the fibre axis.
5. In flax, ramie, hemp, and other bast fibres, the spiral angle is small – less than 6° - so that these fibres are highly oriented and give high strength and low extensibility.
6. In cotton, however, the spiral angle lies between 20° and 30°, and the fibres can extend more easily by stretching the spiral.


Secondary wall:

1. Formed during second phase of growth and makes up about 90% of the total weight.
2. This wall is composed of successive layers of cellulose deposited on the inner side of the primary wall without increase in diameter
3. Strength of the fibre is determined by secondary wall


Lumen:

* Central hollow canal whose dimensions varies over a wide range
* Contains protein, mineral salts and pigments

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