Wednesday, May 27, 2009


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.

1 comment:

Anonymous said...

I am trying to find more of a polyester fabric that I purchased for use in hand lithography. It has a warp and weft of about eighty threads per inch. Looking at the fabric under a ten power linen tester, I can see that none of the threads remain straight... every one is wrinkled.

Can this be accomplished by heating polyester that has already been woven? Or were the threads irregular before being woven.

I hope to find more of this, or make more by manipulating smoother polyester because I use the fabric's oleophilic nature to distribute oil based ink in a wet environment.

Thanks for any input.