Monday, January 11, 2010

Polyester Dyeing

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
1.Polyester fabrics and fibers are extremely strong.
2.Polyester is very durable: resistant to most chemicals, stretching and shrinking, wrinkle resistant, mildew and abrasion resistant.

3.Polyester is hydrophobic in nature and quick drying. It can be used for insulation by manufacturing hollow fibers.
4.Polyester retains its shape and hence is good for making outdoor clothing for harsh climates.
5.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
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.
 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.

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.

Dyeing of polyester with disperse dyes
Dyeing of polyester 2 (Dyeing of Polyester Fabric)
Dyeing of polyester 3(Dyeing of polyester fabric)
Dyeing of polyester 4(Polyester Printing)
Dyeing of polyester 5(Pretreatment of polyester Fabric)
Oligomers and polyester dyeing

What is Oligomer?

Oligomer is a smaller chain length of polyester made up of two or more molecules of basic ethylene terephthlate i.e. dimer or trimer, produced as a side reaction during the manufacture of polyester. The Oligoster because of its smaller chain length is in the form of a fine powder which is entrapped is basic polymer and migrates to the surface during high temperature polyster dyeing. Higher the depth more is the displacement of Oligomer to the fibre surface. Approximately 0.1 % 1.0 % of Oligomer is produced as a side reaction in the manufacture of basic polyester.

Problems caused by Oligomer deposits leading to unlevel dyeings.
  • Filtration effect (inside - out variation) due to build up of Oligomers in package
  • Improper pump pressure due to deposits on pump.
  • Choking of spindle holes
  • Varitation in rate of rise of temperature due to deposits on heating elements.
  • Duller shades
  • Dusting during coning
  • Higher energy costs

Click Here for Problems and their remedies in Processing of Polyester
Click here for color variations in processing of spun polyester filament  
Textile dyeing in supercritical carbon dioxide Click here

What is Trilobal polyester?
Recent advances in fiber technology have resulted in a new type of polyester. In the past, due to its dull appearance, polyester lost out to other fibers, especially rayon. However, with the development of Trilobal polyester, rayon thread may become a thread of the past.


In manufacturing Trilobal polyester, the Trilobal cross section of the fibers creates excellent light reflection, resulting in high sheen. If the desired effect is durability, softness, and brightness, Trilobal poly is perfect for the job.
Following are characteristics of Trilobal poly.
1. Brightness. High sheen for attractive quilting and embroidery designs.
2. Strength. Stronger than rayon, which means fewer thread breaks. Polyester can be used at higher machine speeds than weaker threads, including rayon.
3. Colorfastness. Withstands chlorine. Durable to cleaning and laundering. More resistant to UV exposure than rayon.
4. Controlled elongation (stretch). Outperforms rayon and other polyester threads (such as spun poly).
5. Excellent wet strength. Does not weaken in washings.
6. Abrasion resistant. Higher abrasion resistance than rayon means it does not wear out as fast.
7. More stitch volume. Has a slight 3D effect with less need for underlay or cord. Perfect for satin stitches.
8. More resistant to chemical damage than rayon. Ideal for industrial work-wear garments.
9. More forgiving of poor adjustments or mechanical conditions of the machine.
10. Virtually lint free.
Modification of polyester Click Here
Texturised Yarns Click Here

4 comments:

  1. hello. if a 100% polyester material is dyed, will it bleed? and why?

    thank you very much

    ReplyDelete
    Replies
    1. No it will never bleed because dyes do not react with polyester they get mechanically trapped inside their structure so there is no question of bleeding in polyester

      Delete
  2. Hey why the pressure is taken in polyester jet dyeing machine?

    ReplyDelete
  3. SUMON AHMED, AUST, BANGLADESH
    Is it possible to dye polyester with pigment by applying high temperature ?

    ReplyDelete

Your feed back