The cause of the oligomer and how to remove it

Date:Oct 12, 2020

1. Definition

Oligomer, also known as oligomer, oligomer, short polymer, is a kind of low-molecular substance with the same chemical structure as polyester fiber that exists in polyester fiber, and it is a by-product in the polyester spinning process. . Generally, polyester contains 1% to 3% oligomers.

Oligomers are polymers composed of fewer repeating units, and their relative molecular weight is between small molecules and high molecules. Its English name is "oligomer". The prefix oligo comes from the Greek word ολιγος, which means "some". Most of the polyester oligomers are cyclic compounds formed by three ethyl terephthalates.

2. Impact

Influence of oligomers: colored spots and spots on the cloth surface; white powder produced by yarn dyeing.

When the temperature exceeds 120°C, the oligomer can dissolve in the dye bath and crystallize out of the solution, combining with the agglomerated dye. When it cools, it deposits on the surface of the machine or fabric, causing stains, spots and other defects. The disperse dye dyeing is generally kept at 130°C for about 30 minutes to ensure the dyeing depth and fastness. Therefore, as a solution, light colors can be kept at 120°C for 30 minutes, and dark colors must be pre-treated before dyeing. In addition, dyeing under alkaline conditions is also an effective method to solve oligomers.

3. Comprehensive measures

Specific treatment measures:

3.1. Use 100% NaOH 3% for grey fabric before dyeing. Surface active detergent 1%. Treated at 130℃ for 60min with a bath ratio of 1:10~l:15. The pre-dyeing method has a certain corrosive effect on the polyester fiber, but it is extremely beneficial to the removal of oligomers. For polyester filament fabrics, it can reduce "Aurora", and for short fibers, it can improve the phenomenon of pilling.

3.2. Control the dyeing temperature below 120°C, and use appropriate carrier dyeing methods to reduce the production of oligomers and obtain the same depth of dyeing.

3.3. Adding dispersing protective colloid auxiliaries during dyeing can not only produce leveling effect, but also prevent the precipitation of oligomers on the fabric.

3.4. After dyeing, drain the dye solution rapidly from the high temperature, and drain the solution for up to 5 minutes. Because oligomers are evenly distributed in the dye liquor at a temperature of 100 to 120°C, they tend to accumulate and settle on the dyed fabric when the temperature is below 100°C. However, some heavy fabrics are prone to wrinkles.

3.5. Dyeing under alkaline conditions can effectively reduce the formation of oligomers and remove the remaining oil on the cloth surface, but dyes suitable for dyeing under alkaline conditions must be selected.

3.6. Wash with reducing agent after dyeing, add 32.5% (380Be)NaOH 3—5ml/L, sodium hydroxide 3~4g/L, treat at 70℃ for 30 min, then wash cold, hot, cold, and neutralize with acetic acid .

4. For yarn white powder

1) The thorough method is the high temperature drainage method.

For example, immediately open the drain valve after the temperature of 130 ℃ is completed (120 ℃ is also possible, but not lower, because 120 ℃ is the polyester glass transition point).

●That said, it seems simple, but the most important thing is that the safety problem is the most difficult: the sound and mechanical vibration at the moment of high-temperature discharge are amazing, and the aging machinery is easy to crack or loose screws, and the machinery is cracked. Will explode (pay special attention).

●If you want to refit, please go to the original machinery factory to design the refit. Don't just use human life as a trifle.

●There are two ways to drain the liquid into the water tank and to the outside of the atmosphere.

●Pay attention to the phenomenon of backlash after the discharge (experienced dye vat manufacturing company knows it well).

●High temperature drainage has the advantage of shortening dyeing, but factories with poor reproducibility are troubled

2) For factories that cannot discharge liquid at high temperature, Oligomer detergent can be used to replace detergent in the reduction and cleaning process, but the effect is not 100%

●Wash the vat frequently after dyeing, wash the vat once after about 5 vats for medium and dark colors.

●If the current liquid dyeing machine has a lot of white powder, the first priority is to wash the vat.

5. Some think that the price of table salt is cheaper

Some people think that the price of table salt is cheaper, and table salt can be used to replace Yuanming powder. However, it is better to dye light colors with Yuanming powder than table salt, and for dark colors, table salt is better. Whatever is appropriate, it must be applied after testing.

6. The relationship between sodium sulfate and salt

The relationship between sodium sulfate and salt consumption is roughly as follows:

6 parts anhydrous Na2SO4=5 parts NaCl

12 parts hydrate Na2SO4·10H20=5 parts NaCl

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