Properties of Polyester

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, In spite 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.

Author : Bhushan Borse (Research Student) UICT, Mumbai, India

Dye carriers

Dye carriers are accelerators that assist in the dyeing of synthetic fabrics in a shorter time at a lower temperature. They are particularly used for dyeing polyesters with disperse dyes, although they were originally developed for cellulose acetate. There are a number of carriers commonly used for polyester fibres. Some of the good dye carriers are o-phenyl phenol and it’s monochloro derivative, p-phenyl phenol, diphenyl, monomethyl naphthalene, trichlorobenzene, dimethyl terephthalate and methyl salicylate. Other dye carriers in common usage are o-dichlorobenzene, diphenyl ether, n-butyl phthalimide, chloromethoxy ethanol, methyl cresotinate, alkyl and aryl benzoates and tetralin. The dye carrier imbibes deep shades on the polyester and blended fabrics. Acrylic and nylon fibers also can be dyed using dye carriers but this approach is more expensive than the other alternatives available.
In practice, the choice of the dye carrier is governed by its general effectiveness, toxicity, economics and environmental acceptance. Some of the phenolics and chloro-derivatives are getting eliminated. In a typical operation for dyeing polyester fiber, the dye carrier suitably emulsified in water is used in both the exhaust method at atmospheric pressure as well as in high temperature beam dyeing. After dyeing, the dye carrier is removed from the fabric by an after-scouring process. Whereas dye carriers like the chlorobenzenes are used by emulsification, the phenyl phenols can be used as their water soluble sodium salts along with an acid-liberating agent like ammonium phosphate. At about 100C, the free phenol liberated forms the active carrier which is later removed by alkaline scouring. Butyl benzoate is another successful carrier for use in polyester dyeing at the boil at atmospheric pressure.
The dye carriers are generally used with a leveling agent on polyester/wool mixtures in a high temperature process. The formulations usually consist of around 70% active ingredients (one or more dye carriers), 15% leveling agent and 15% solubilising agent. Depending on the color and shade, the dye carrier used is in a variable range of 2-10% of the textile weight.

author : Laxmikant S. Jawale