Advertorial: Oligomer removal

Excerpt: Polyester fabric is sensitive to dye migration. The actual dye migration on Polyester fibre surface occurs as a result of migration of oligomers of Polyester from core to fabric surface.

Introduction

NOW a days consumer has become more conscious about looks and feel of garment. Slight mismatch or shade variation is not accepted at consumer's end. Polyester fabric is sensitive to dye migration. The actual dye migration on Polyester fibre surface occurs as a result of migration of oligomers of Polyester from core to fabric surface.

Oligomers are low molecular weight byproduct, during polymerization reaction between diethylene glycol with terephthalic acid to obtain Polyester. They have different structures and are classified according to the number of units they contain.

These oligomers exhibit high thermal sensitivity, and hence they migrate from fabric/ fibre core to surface during high temperature Polyester dyeing. Higher the depth of dye, more is the displacement of Oligomer to the fibre surface.

These oligomers are insoluble and form agglomerate forming bigger crystals. Presence of oligomers can lead to nucleation and growth of dye crystals resulting in dye spots, unevenness, and poor fastness.

These oligomers pose following problems

  1. White deposit on yarn/ package
  2. Deposition on machine wall
  3. Unlevel dyeing
  4. Clogging of spindles
  5. Dusting during rewinding, knitting and weaving
  6. Filtration effect (inside – out variation) due to build up of Oligomers in package.
  7. Improper pump pressure due to deposits on pump
  8. Variation in rate of rise of temperature due to deposits on heating elements.
  9. Duller shades
  10. Higher energy requirement
  11. Increase friction value of yarn resulting into more breakages of yarn in winding.

Keeping in mind above problems and remedies, Sarex has developed a novel process using Eliminator-GLO to resolve problem of Oligomers in Polyester dyeing.

Unique features

An effective oligomer removing agent used during polyester dyeing.

  • Enables uniform and solid dyeing.
  • Reduces the machine cleaning cycles as it keeps the oligomers in suspended/dispersed forms and prevents their redeposition.
  • One can use the product along with caustic for machine cleaning during polyester dyeing.
  • If we use the product in dye bath, improved washing fastness can be obtained.
  • Improves the combing quality of stock-dyed material.
  • No retardation of disperse dyes: No negative effect on colour yield or fastness.

Mechanism

Polyethylene terephthalate polymers have a certain proportion of low molecular weight compounds which are referred to as oligomers, produced as a side reaction during the manufacture of polyester. At temperatures above the glass transition temperature of polyethylene terephthalate, oligomers migrate out of the fibre on to the surface. These oligomers have a tendency to deposit on the surface of the polyester and on the dyeing machine on cooling. Since oligomers cannot be dyed with the disperse dyestuffs, they appear as a white dusting powder on the dyed goods.

Eliminator-GLO has a tendency to keep the oligomers in suspended/dispersed form. Eliminator-GLO will prevent the re-deposition of oligomers onto the fabric allowing more oligomer to go down the drain.

Application process

Eliminator-GLO Dilution Method

Take 01 part of Eliminator-GLO and dilute it with 05 parts of warm water with stirring. Continue stirring to get homogenous product.

Avoid adding concentrated product directly in the machine.

Experiment

To study the efficiency of Eliminator-GLO by oligomer filtration test

A definite amount of oligomer is taken in the test solution. Same parameters to be kept as that of polyester dyeing. The temperature was raised to 135°C and then it was lower down to 80°C. The solution is filtered with black filter paper.

Oligoer content determination methodm

Place 10 gm of polyester yarn/fabric in Soxhlet extractor. Take adequate quantity of solvent (one and half cycle) and extract the sample for 4hrs. Recover bulk of solvent by distillation and evaporate the extract to dryness. Further dry the residue in flask by drying oven at 105°C for 4hrs or till constant weight is obtained. Weigh the Flask

Calculation

% Oligomer content = (Weight of residue X 100)/ Weight of specimen

Where, Weight of residue= (Weight of flask + residue) – initial weight of flask

Thus with Eliminator-GLO treatment, 70-80% oligomer removal is obtained in single treatment.

Author details

Dr. Naresh Saraf

Sarex Chemicals A division of Saraf Chemicals Ltd., Andheri (W), India