Wash fastness on polyester is usually decided after the dyeing is finished, in a step that gets five minutes of attention: clearing. Dye that never fixed sits on the fibre surface. If it is not removed, it bleeds in the first domestic wash and rubs off onto a white cloth in the shop. The fix is a reductive clearing step — and the economics sit less in the chemical than in the rinses and the neutralisation you no longer have to run.
Product covered in this guide: Acid Cleaning Agent — a white powder at pH 11, supplied in 25 kg bags for polyester, polyester blends and synthetic fibres. It is listed in the Energy Solutions range; ask for the TDS and a sample if you want to trial it on your own dye lots.
Key takeaways
- Unfixed disperse dye sits on the fibre surface and will not rinse off with water — it has to be reduced first.
- Over-clearing attacks dye that was correctly fixed; the symptom is a shade shift, not better fastness.
- An alkaline clearing agent that holds pH 11 removes two machine fillings and one 60–90 minute neutralisation cycle per batch.
What an Acid Cleaning Agent Actually Removes
After disperse dyeing, a fraction of the dye is not fixed inside the fibre. It sits on the surface as loose pigment and oligomer. It is not dirt, and it does not rinse off with water alone — it needs to be chemically changed into something water-soluble before it will leave.
That is what an acid cleaning agent does as a reductive clearing step: in an alkaline bath it reduces the surface dye, breaking the chromophore so the fragment dissolves and rinses away. Soaping with a surfactant removes some of it; reduction removes the rest. That difference shows up directly in wash and rub fastness.
Three Ways Clearing Goes Wrong
| Failure | What you see | Usual cause |
|---|---|---|
| Under-clearing | Colour bleeds in the first wash; poor rub fastness | Too little reducing power, hold too short, or pH too low |
| Over-reduction | Shade shifts or dulls, especially on sensitive dyes | Excess dosage, temperature too high, or hold too long |
| Wrong pH | Incomplete reduction, or a bath that cannot hold the condition | Acid contamination, or no alkaline buffer |
The first two look similar in a lab report and opposite in a bath. Under-clearing leaves dye on the fibre; over-reduction attacks dye that was correctly fixed. Both are avoided by running the step inside a defined window instead of adding more chemical until the shade looks right.
Where the Water and the Time Go
A conventional clearing route looks like this: dye, drop, rinse, clear, rinse, neutralise, rinse. Every rinse is a full machine filling; the neutralisation step alone commonly runs 60–90 minutes. A reductive clearing agent that removes two of those steps changes the arithmetic.
An acid cleaning agent that is stable in alkaline conditions and in hard water removes two of those steps from the sequence: two full machine fillings per application, and one acid neutralisation cycle of roughly 60–90 minutes. On a machine running three batches a day, that is the difference between four batches and five.
Acid Cleaning Agent: The Parameters That Matter
| Parameter | Value | Why it matters |
|---|---|---|
| pH | 11 | The reduction only works in alkaline conditions; the bath must stay there |
| Physical form | White powder | Dosed by weight; dissolves in the clear bath |
| Stability | Hard water and alkaline solution | No softening step, no precipitation in the bath |
| Incompatible with | Strong oxidising agents, acid | An oxidant consumes the reducing power; an acid drops the pH out of the window |
| Packaging | 25 kg bag | Standard dry-goods handling |
Typical process window
The figures below are the industry-typical range for this class of product. They are a starting point, not a substitute for your own TDS — confirm the exact values with the supplier before setting a recipe.
| Parameter | Typical range | Notes |
|---|---|---|
| Dosage | 1–3 g/L | Scale with depth of shade and oligomer load |
| pH | 10.5–11.5 | Below 10.5 the reduction stalls |
| Temperature | 70–85 °C | Higher temperatures raise the over-reduction risk |
| Hold time | 15–30 min | Start short, extend only if fastness fails |
| Liquor ratio | 1:10–1:20 | Match the machine and the fabric weight |
Product Specifications
| Property | Value |
|---|---|
| Product name | Acid Cleaning Agent |
| Physical form | White powder |
| pH (as supplied) | 11 |
| Stability | Stable in hard water and alkaline solution |
| Incompatible with | Strong oxidising agents, acidic products |
| Applications | Dyeing and washing factories |
| Fabrics | Polyester, polyester blends, synthetic fibres |
| Packaging | 25 kg bag |
Acid Cleaning Agent Dosage and Cost per Batch
Clearing dosage scales with the depth of shade and the oligomer load, not with fabric weight alone. A heavy black or navy carries more surface dye than a pastel, and a fibre with a high oligomer content needs more reducing power to lift the waxy deposit. Start from the TDS range, then adjust on the fastness result rather than on appearance.
The cost comparison that matters is not price per kilogram against another acid cleaning agent. It is cost per batch, including the fillings and the neutralisation cycle the step removes:
| Cost line | What to count |
|---|---|
| Clearing chemical | Dosage × bath volume × price per kg |
| Rinse water | Fillings × machine volume × water and effluent cost |
| Steam | Heat-up time for each filling that is no longer run |
| Machine time | The 60–90 minute neutralisation cycle |
An acid cleaning agent that looks 20% more expensive per kilogram and removes two fillings and one neutralisation cycle is cheaper per batch. That is the comparison to put in front of a dyehouse manager.
How to Verify Clearing
Clear a dye lot, then measure the same three things before and after:
- Wash fastness. ISO 105-C06, assessed on the grey scale. This is the number buyers ask for.
- Rub fastness. ISO 105-X12, dry and wet. Wet rub is where under-cleared polyester fails first.
- Surface dye. A simple solvent wipe on a white cloth, or a reflectance reading against the same lot before clearing.
Run the test on your own dye selection, not on a reference card: some disperse dyes shift shade under reduction and others do not. If the shade moves more than your tolerance, the answer is a shorter hold or a lower temperature, not a different product. ISO 105-C06 sets out the wash method; the grey scale judgement is what the buyer sees, and what OEKO-TEX audits check. Where a brand screens suppliers on chemical conformance, ZDHC MRSL is the other framework they will ask about.
Why Polyester Needs This Step and Cotton Doesn’t
Reactive dyes on cotton form a covalent bond with the fibre. Dye that does not react hydrolyses, becomes water-soluble, and rinses away in the soaping step. Disperse dyes on polyester work by dissolving into the fibre — there is no bond to break — and the dye that stays on the surface is still the same insoluble molecule. Water will not move it. It has to be reduced first.
That is why a cotton route can be cleared with a surfactant and a hot rinse, while polyester needs a reductive step — the reductive clearing chemistry that separates a passing lot from a failing one. Mills that copy a cotton clearing recipe onto a polyester line usually end up with acceptable appearance and failing wash fastness, which surfaces at the buyer’s lab rather than in the dyehouse.
The Rinse Arithmetic
Take a machine that runs three batches a day, with a clearing sequence of rinse, clear, rinse, neutralise, rinse. Each rinse is one full filling. A clearing step that holds its own pH removes two fillings and the neutralisation cycle from that sequence:
| Item | Conventional route | With an alkaline clearing agent |
|---|---|---|
| Rinses after clearing | 3 | 1 |
| Acid neutralisation | 60–90 min | Not required |
| Machine fillings per batch | 3 | 1 |
| Water per batch (1 m³ fillings) | 3 m³ | 1 m³ |
| Batches per shift (8 h) | ~3 | ~4 |
The saving is not theoretical, but it is also not automatic: it only appears if the bath actually stays alkaline. A leaking acid valve or a rinse that carries acid forward cancels the benefit and the step fails at the same time.
Effluent load is part of the same calculation. The reduction products add to the COD that the treatment plant has to handle, and buyers increasingly ask for documentation under REACH before a chemical goes into an approved list.
What to Log Per Batch
Reductive clearing is the step where a dyehouse most often trusts its eyes. Four numbers per batch turn it into a process:
| Record | Why |
|---|---|
| pH at start and end of the hold | A drift below 10.5 explains most ‘it did nothing’ batches |
| Temperature and hold time | Over-reduction shows up here first |
| Dosage actually weighed | Dosing by scoop is the second most common cause of variation |
| Shade reading against the approved standard | Catches over-reduction before the batch is packed |
Keep the fastness result on the same sheet. When a buyer asks why one lot passed and another did not, the answer is usually in these four columns rather than in the dye lot.
What It Won’t Do
- It won’t fix a badly selected dye. If a dye has poor wet-fastness by nature, clearing cannot add what is not there.
- It won’t replace soaping for every dye class. Some shades still need a surfactant step to lift oligomer.
- It isn’t for acid dyeing. Nylon and wool rely on a different chemistry and a different pH window.
- It won’t mix with acid or oxidant. Both destroy the condition the reduction needs.
- It won’t fix uneven dyeing. Clearing works on the surface; it does not redistribute dye inside the fibre.
Frequently Asked Questions
What is a reductive clearing agent used for?
Removing unfixed disperse dye from the surface of polyester after dyeing, so wash and rub fastness meet the buyer’s specification.
Why is an ‘acid cleaning agent’ at pH 11?
The trade name is historical. On the line it works as an alkaline reducing system: the bath must be held at pH 11, and an acid shift stops the reduction. Treat the name as a product label, not a description of the bath.
Can I run it in hard water?
Yes. It is formulated to stay stable in hard water and in alkaline solution, so no softening step is required.
What happens if the bath turns acidic?
The reduction stops. An acid shift is the most common reason a clearing step ‘does nothing’ — check the pH before adding more product.
Can I mix it with hydrogen peroxide or another oxidant?
No. Strong oxidising agents consume the reducing power and the step fails.
How much water does it save?
Two full machine fillings per application, plus one acid neutralisation cycle of roughly 60–90 minutes.
Does it affect the shade?
It can, on dyes that are sensitive to reduction. Run a short hold first and check the shade against your tolerance before extending the time.
Which fabrics is it for?
Polyester, polyester blends and synthetic fibres after disperse dyeing, including wool/polyester, polyester/cotton and polyester/nylon blends.
The Short Version
An acid cleaning agent is a short step with an outsized effect on fastness. Run the reductive clearing step at pH 11, keep the oxidants and acids out of the bath, and verify with ISO 105-C06 and ISO 105-X12 rather than by eye. The water and time saving — two machine fillings and one neutralisation cycle — is the part that shows up in the monthly numbers.
Related Reading
If your route also starts with starch-sized woven greige, the desizing step decides dye uniformity before the dye ever goes in. For denim washing enzymes, see Water Free Powder Enzyme; for low-temperature pretreatment chemistry, see low-temperature pretreatment agents; and for PFAS-free alternatives in the washing process, see Eco-Washing.
Next Step
Send us your current clearing recipe, the dye class and the fastness specification you have to hit. We will return a dosage recommendation and a test protocol you can run on one machine.
[…] Related reading. For the step that decides polyester fastness after dyeing, see Acid Cleaning Agent: reductive clearing for polyester. […]