Deaerating Surfactants

In densely woven and heavy fabrics, air trapped in the pores keeps the liquor out of that spot and leaves a light speck in the dyeing. Deaerating surfactants wet the cloth and destabilise that bubble at the same time. Two products in the family.

Why does air stay inside the fabric?

Dry fabric is a network of pores, and every one of them is full of air. For the liquor to get in, that air has to get out; dense construction, high twist and heavy weight all make the exit harder. Air that cannot leave is trapped in the pore as a bubble, and liquor never reaches that point.

The result shows up in the dyeing: the spot under the bubble stays light, and when the cloth is opened out it reads as a speck or a pinpoint fault. The same mechanism operates on a larger scale in the pad trough, where entrained air changes the pick-up from point to point.

Is a deaerating surfactant the same as an antifoam?

Both deal with air bubbles, but in different places.

Deaerating surfactants wet by lowering surface tension and at the same time destabilise the bubble. An antifoam contributes nothing to wetting; it only collapses foam. The two are not interchangeable, though they can appear in the same recipe.

Where does it make a difference?

On densely woven polyester and microfibre, on heavy gabardine and canvas, and on HT jet programmes that fill quickly. On those fabrics a standard wetting agent lowers the surface tension but cannot get the trapped air out.

On pad-batch and pad-steam ranges the reason is even pick-up. A deaerating surfactant makes the cloth take the same amount of liquor along the run, and as the variation in pick-up falls, so does the shade variation across the width: pending from the client.

Dosage and verification

Dosage on a deaerating surfactant follows how tight the fabric is and how fast the machine fills. The same product that is enough at a low dose on a loose knit wants a markedly higher dose on heavy canvas.

Verification is done in the laboratory with the sinking-time test, set up with the real bath composition. When the fabric specimen is dropped into the solution, both the sinking time and the moment bubbling from the surface stops are recorded; the difference between two products usually shows in the second reading.

Why is low foam a condition?

If the deaerating surfactant foams itself, it undoes its own work. Foam collecting on the surface delays the release of the air coming out of the cloth and cuts circulation in a jet. Products in this family are therefore formulated to be low-foaming, and foam behaviour is judged alongside wetting speed when selecting one.

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