For disperse dye manufacturers using Naphthalene (NNO), with laboratory data on Jiefa ES-3 sodium lignosulfonate dispersant versus naphthalene-type dispersants.
Conclusions
- Oligomers come from the polyester, not from the dye. About 1–3 % of the fibre is oligomer, mostly cyclic trimer. It comes out into the bath at 130 °C and forms crystals as the bath cools. The fibre decides how much there is.
- But oligomer in the bath also makes disperse dye particles stick together at top temperature.Whether the dye survives this is decided by the dispersant inside the dye, not by the dyeing house.
- Naphthalene (NNO) has a heat stability below 110 °C and fails the 130 °C dispersibility test (E/1). At top temperature the dye is already unprotected, even before oligomer arrives. A naphthalene-dispersed dye leaves the whole oligomer problem to the dyeing house.
Jiefa ES-3 costs about the same as Naphthalene (NNO), or slightly more, and keeps the dye stable through 130 °C with polyester in the bath: 0.25 bar package-dyeing pressure and residue grade 4–5, against more than 1.0 bar and grade 1–2 for a naphthalene-type dispersant.
What oligomers are, and what they do
Polyester contains 1–3 % of short polymer chains left over from polymerization, mostly cyclic trimer. At room temperature they stay inside the fibre. At 130 °C the polymer opens up, the oligomer moves to the fibre surface and part of it passes into the bath. It dissolves very poorly in water, so it appears as fine particles once the bath is saturated and forms crystals as the bath cools. Every polyester lot brings its own oligomer into the dye bath; microfibers, cationic-dyeable polyester and long holds at 130 °C bring more.
The visible half of the problem is familiar to every dyeing house: a white powder on fabric and yarn that gives deep shades a white frost and a dull look, a harsh handle, and scale on vessel walls, nozzles, filters and heat exchangers that means more frequent dyeing machine cleaning. Package dyeing, warp beam dyeing and airflow dyeing machines suffer most, because yarn layers and a low liquor ratio concentrate the deposit.
The invisible half is what this article is about. Oligomer particles in a hot bath are hydrophobic, and dye particles stick to them and to each other. They pull dye particles and free tar into a sticky mass and speed up the aggregation of sensitive dyes such as disperse turquoise blue, magenta and disperse violet. The result is dye specks, dye blotches and tar stains that look exactly like a dye quality defect. The dyeing house blames the dye; the dye manufacturer, whose 130 °C filter test was clean, blames the fibre.
Why the standard tests do not show it
The 130 °C high-temperature dispersibility test (GB/T 5541) and the 71 °C test (AATCC 146) are run in clean water, with no fibre and no oligomer. A dye can pass both and still fail in a bath full of polyester. Oligomer resistance can only be seen in a test that contains fibre. The most practical one is laboratory package dyeing with the differential pressure recorded: polyester packed on a perforated tube releases its own oligomer at 130 °C, and if the dye aggregates, the pressure across the package rises. A flat pressure trace means the dispersant kept the dye stable with oligomer present.
Two kinds of dye manufacturer, two different experiences
Dye manufacturers who use quality lignosulfonates rarely hear about oligomer-related specks. A lignosulfonate with high heat stability stays on the dye particle through the 130 °C hold, keeps its electrostatic and steric stabilization working while oligomer enters the bath, and keeps the oligomer particles suspended so that more of them leave with the drain. They paid more for the dispersant, and oligomer control came with it.
Dye manufacturers on Naphthalene (NNO) hear about it all the time, usually without recognizing it. Naphthalene (NNO) is cheap, mills fast and stains little, but its heat stability is below 110 °C and it carries about 20 % salt. In our laboratory two commercial samples both rated E/1 with heavy aggregation in the 130 °C test, in clean water; oligomer only makes it worse. The dyeing house then does what it can: hot draining at 120–130 °C, alkaline dyeing at pH 9–9.5 with alkali-stable dyes, hot reduction clearing and oligomer-dispersing auxiliaries. All of these remove oligomer that has already come out. None of them can stop the dye from aggregating during the 130 °C hold, because that is decided by the dispersant inside the dye. The naphthalene user did not avoid the oligomer problem. It passed it on. On open, lightweight fabric such as saree material the frost and specks are easy to miss; on packages, dense knits, deep shades and export orders they are not.
ES-3: a lignosulfonate priced against naphthalene
ES-3 is the general-purpose grade of the Jiefa ES series of sodium lignosulfonate dispersants, made from natural softwood lignin and purified by ultrafiltration. It costs about the same as Naphthalene (NNO), or slightly more where very cheap naphthalene is being bought, is used at a similar dosage, and fits into the same sand-milling process. What the naphthalene user gains is the property that matters at 130 °C: heat stability of 150 °C and a salt content of about 1 %. The dispersant stays on the dye when oligomer enters the bath, the dye does not aggregate, and more of the oligomer leaves with the drain instead of staying on the goods and the machine.
One honest limit: ES-3 stains polyester more than naphthalene does (ΔE about 7 against 0.2–1.4 for Naphthalene (NNO), measured with the dispersant alone on white polyester). For navy, black and other deep shades this does not matter. For bright and pale shades it should be checked on the specific dye, and we do this together with the customer before any change.
Laboratory results: ES-3 versus naphthalene-type dispersants
Indicator | Naphthalene (NNO), two commercial samples | MF (naphthalene-type) | Jiefa ES-3 |
Chemistry | Naphthalene sulfonate–formaldehyde condensate | Methylnaphthalene sulfonate–formaldehyde condensate | Sodium lignosulfonate, softwood, ultrafiltered |
Heat stability | < 110 °C | 130 °C | 150 °C |
High-temperature dispersibility (130 °C) | E/1, heavy aggregation | 23 s | 19 s |
Dispersibility at 71 °C | A/3 (AATCC class / residue grade) | 12 s | 12 s |
Total salt content | 20.61 % / 20.34 % | 4.89 % | 1.16 % |
Reducibility | 0.15 % / 0.14 % | 3.02 % | 1.98 % |
Polyester staining by dispersant alone, ΔE (CIE) vs. undyed blank | 0.15 / 1.41 | 6.35 | 7.0 |
Table 1. Routine indicators measured in the Jiefa application laboratory under the same protocol (HG/T 3507, HG/T 3399, GB/T 5541-2017); dispersibility is reported as filtration time or as AATCC 146 class and residue grade depending on the test series.
Package dyeing with polyester in the bath: ES-3 versus MF
Cake: Disperse Blue 79, chlorine-type; cake to dispersant 1:0.6; both dispersants milled to D90 < 1 µm under identical conditions; laboratory package dyeing at 3.0 % owf with the differential pressure recorded throughout. The polyester in the package releases its own oligomer during the run, so this is the closest bench test to a production dye bath.
Test | ES-3 | MF (naphthalene-type) |
Heat stability (HG/T 3507) | 150 °C | 130 °C |
130 °C dispersibility, filtration time (GB/T 5541) | 19 s | 23 s |
Package dyeing, max differential pressure | 0.25 bar, slight peak | > 1.0 bar at 97.7 °C, run stopped |
Package dyeing, dye residue grade | 4–5 | 1–2, heavy precipitation |
Table 2. ES-3 versus MF on a chlorine-type Disperse Blue 79 press cake.
Figure 1. Package dyeing at 3.0 %. With the naphthalene-type dispersant the pressure passed 1 bar before 100 °C and the package came out grey and blotchy; with ES-3 the pressure stayed flat through the 130 °C hold and the package dyed level. Same cake, same milling, same machine.
FAQ
Oligomer comes from the polyester. How can a dye dispersant help? It cannot change how much oligomer the fibre releases. It decides whether the dye aggregates around it. The fibre sets the amount of oligomer; the dispersant sets whether it takes the dye down with it.
Are hot draining and alkaline dyeing not enough? They remove oligomer that has already come out of the bath. They do nothing during the 130 °C hold, which is when the dye aggregates. The two measures deal with different halves of the problem.
Will ES-3 affect my bright and pale shades? Possibly, because it stains polyester more than naphthalene. Navy, black and deep shades are not affected. For bright and pale shades we run the comparison on your dye before you switch; many manufacturers keep naphthalene in a few bright formulations and move everything else to ES-3.
Test ES-3 on your own dye
The fibre brings the oligomer; the dispersant decides whether it becomes a complaint. Send us a press cake you currently make with Naphthalene (NNO). We will mill it with ES-3 next to your dispersant, run the 130 °C and package dyeing tests, check staining on your shade, and send you the results side by side.
