How to Control Oligomer in   Polyester Processing

Dr. N. N. Mahapatra

Business Head (Dyes), Shree Pushkar Chemicals & Fertilizers Ltd.

All polyester Fibres contain a certain proportion of oligomers.   The oligomer is a smaller chain length of polyester made up of two or more molecules of ethylene terephthalate, i.e., dime or termer, produced as a side action ring manufacture of polyester.  The oligoether because of its smaller chain length is in the form of a fine powder that is entrapped in basic polymer and migrates out of the textile arterial during high-temperature polyester dyeing and is deposited in an aggregated form on the material and in the dyeing machine as the liquor cools Higher the depth ore is the displacement of the oligomer to the fiber surface.  Approximately 0.1 %to 1 .0 % of the oligomer is produced as a side reaction in the manufacture of basic polyester. Oligomers are like cholesterol. It has to be prevented by various means during and before dyeing otherwise the subsequent processes get affected.

Problems caused by oligomer deposits are different in the case of fiber dyeing, yarn dyeing, and fabric dyeing.

Oligomer deposition on the substrate and machine can cause considerable problems in the dyeing of polyester The production of the oligomer is dependent upon the quantity of low molecular polyester produced during the polyester synthesis. Under high-temperature processing, these oligomers exude from within the polyester fiber and redeposit. Due to their small size, they remain undyed during the process, aggregate, and can be seen as a grey “frosty “deposit on the substrate. They can also gather in the machine itself, and then redeposit as sticky lumps on the polyester. If the polyester quality is high, then the quantities remain small and are usually removed during the machine cleaning process between dyeing production schedule changes from dark to light shade processing. The white powder is collected from the inner wall of the dyeing machines, rewinding machines, etc. The oligomer percentage is calculated by the Solvent Extraction method from polyester fiber (grey and dyed).

It has been found that the oligomer percentage is more in heavy dark shades of polyester fiber as compared to light shade polyester fiber.

It is entirely based on practical experience working with dyed polyester fiber in spinning and dyed polyester yarn working in knitting and weaving machines.                                           

M/C cleaning procedure to clean oligomer scaling from dyeing machines

Objective: Depending on the scaling of oligomer deposits inside the dyeing vessel, carrier holes are closed, white powder deposits, etc. then accordingly the type of machine cleaning procedure can be selected. If possible, once in a while the pump can be taken out and see if any oligomer scaling is there.

Such a type of machine cleaning is required because chances are their oligomer deposits inside the pipelines also.

Complete M/C cleaning (Once a year)

Chemicals to be used

  1. Strong dispersing agent – 5 GPL
  2. CAUSTIC – 15 GPL
  3. HYDROS- 1 GPL
  4. Non-Ionic Detergent – 0.5 GPL

Steps:

  1. Take one empty carrier in the m/c
  2. Add the above chemicals
  3. Run at room temp for 10 mins
  4. Raise temp to 130 deg c. and hold the temp for 4 hrs., pump running.
  5. Stop the pump and heating.
  6. Leave it for 4-5 hrs
  7. Take out the empty carrier
  8. Wipe the empty carrier & inside of the dyeing vessel with hessian cloth. it will shine like a new carrier.
  9. Put the other empty carrier
  10. Leave it for 4-5 hrs
  11. Again, start pump raise to 135 deg c and hold for 2 hrs.
  12. H.T. drain
  13. hot wash at 95 deg c with non-ionic detergent -0.25 GPL, for 10 mins.
  14. Drain
  15. Neutralize at 95 deg with acetic acid -2 GPL.
  16. Drain
  17. Cold wash
  18. Unload empty carrier.
  19. Wipe the empty carrier   & inside of the dyeing vessel with hessian cloth. it will shine like a new carrier.

Total time required: 18-19 Hours.

Routine cleaning once a month

Chemicals to be used:

  1. Strong Dispersing Agent – 2 GPL
  2. Caustic – 5 GPL
  3. Hydros – 0.5 GPL
  4. Non-ionic detergent– 0.25 GPL

Steps:

  1. Take one empty carrier in the m/c
  2. Add the above chemicals
  3. Raise temp to 135 deg c.
  4. hold for 1 hr with the pump running.
  5. h. t. drain
  6. Neutralize with acetic acid -1 GPL
  7. Hot wash with non-ionic detergent – 0.25 GPL at 90 deg c. for 10 mins.
  8. Hot drain
  9. Cold wash
  10. Unload empty carrier.
  11. Repeat the same process for the other empty carrier
  12. Both times wipe the empty carrier &inside of the vessel using hessian cloth. both will shine like new

Total time required: 7-8 hours