Polyester filament

Polyester

Polyester is a term often defined as “long-chain polymers chemically composed of at least 85% by weight of an ester and a dihydric alcohol and a terephthalic acid”. In other words, it means the linking of several esters within the fibers. Reaction of alcohol with carboxylic acid results in the formation of esters.

Polyester also refers to the various polymers in which the backbones are formed by the “esterification condensation of polyfunctional alcohols and acids”.

Polyester can also be classified as saturated and unsaturated polyesters.

Saturated polyesters refer to that family of polyesters in which the polyester backbones are saturated. They are thus not as reactive as unsaturated polyesters. They consist of low molecular weight liquids used as plasticizers and as reactants in forming urethane polymers, and linear, high molecular weight thermoplastics such as polyethylene terephthalate (Dacron and Mylar). Usual reactants for the saturated polyesters are a glycol and an acid or anhydride.

Unsaturated polyesters refer to that family of polyesters in which the backbone consists of alkyl thermosetting resins characterized by vinyl unsaturation. They are mostly used in reinforced plastics. These are the most widely used and economical family of resins.

 

Characteristics of polyester

Polyester fabrics and fibers are extremely strong.

Polyester is very durable: resistant to most chemicals, stretching and shrinking, wrinkle resistant, mildew and abrasion resistant.

Polyester is hydrophobic in nature and quick drying. It can be used for insulation by manufacturing hollow fibers.

Polyester retains its shape and hence is good for making outdoor clothing for harsh climates.

It is easily washed and dried.

 

Uses of Polyester

The most popular and one of the earliest uses of polyester was to make polyester suits – all the rage in the 70s. Polyester clothes were very popular. Due to its strength and tenacity polyester was also used to make ropes in industries. PET bottles are today one of the most popular uses of polyester. Dyeing of polyester

Pretreatment of polyester before dyeing

The material usually contains small amounts of water-soluble or emulsifiable preparations which can be readily washed off. With tops, loose fibers and smooth or textured yarns rinsing for 10 min with cold water is often sufficient. Depending on the degree of contamination of the substrate one-bath scouring and dyeing of grey , unset piece goods of textured yarns is possible.

If the material is highly stained with the spinning oils or other contaminants then it is advisable to give a soaping treatment with stain removing detergent at 75 0 C for about 15-20 min. Or it may be directly added to the dyebath along with the dyes and chemicals.

 Dyeing process

Related topic

Disperse dyes

 The dyeing of polyester is usually carried out in following forms,

loose fibres and tops

yarn and fabric
piece goods (jet, overflow and beam dyeing machine)

 

The dyeing of hydrophobic fibers such as polyester with disperse dyes may be considered as a  process of dye transfer from a liquid phase to a solid organic solvent.

Stages in polyester dyeing

There are three main stages in a polyester dyeing cycle

Dissolution :- of the dye in water in the form of fine dispersion.

Distribution or adsorption :- adsorption of the dissolved dye onto the fiber surface.

Diffusion:-penetration of the dye molecules deep inside the inner cores of the fiber.

 The important  parameters in a polyester dyeing cycle

1.pretreatment process.

2.dye solubility ,dye dissolution, and dye selection.

3.material to liquor ratio.

4.dyeing temperature.

5.dyeing duration.

6.leveling and retarding agents.

7.dispersing agents.

8.removal of excess dyes from the fibers.

9.oligomers  and their removal.

10.reduction clearing.

11.soaping treatment.

12.use of dyeing career.

13.correction of faulty dyeing.

14.stripping of the dyes.

Type of disperse dyes

Normally, Disperse dyes are separated into three types: one is low energy type, which are used for carrier dyeing and thermosol dyeing, the other is high energy type, suitable for HT/HP dying (or exhausting dyeing ), the thirdly is medium energy type, they are suitable for all the dyeing methods.