Micro Silicone Emulsions

Micro silicone emulsions are amino-functional silicones whose droplet size has been taken below the wavelength of visible light. The emulsion looks clear, the silicone penetrates the yarn body, and the softness it gives comes from inside the yarn rather than from the surface.

What separates a micro-emulsion from a macro-emulsion?

The difference is particle size, and particle size decides where the product ends up. The droplets of a micro-emulsion are small enough to move in between the fibres inside the yarn; a macro-emulsion stays largely on the fabric surface.

The result shows in the handle. Cloth finished with a micro silicone feels full and solid in the hand. A macro silicone gives the same cloth more surface slip and flow. One does not replace the other, and many recipes use both.

Clarity of the emulsion is a side indicator here: because the droplets are smaller than the wavelength of visible light, the emulsion looks transparent. A micro-emulsion that has started to go cloudy in store is usually losing its stability.

Why does amino silicone yellow?

What gives the softness also causes the yellowing. Amino groups anchor to the charge on the fibre and tie the silicone chain to the cloth, but those same groups oxidise under heat and air into coloured structures. The higher the stenter temperature, and the longer the cloth stays in the oven once dry, the more visible the yellowing.

Three places to look in practice:

1. Amine value. On whites and pastels, low amine value or blocked-amine grades are preferred. On dark shades a high amine value causes no trouble and gives a fuller handle.
2. Stenter regime. Every second the cloth spends in the oven after it is dry goes onto the yellowing account. Needlessly high temperature is the most common cause.
3. Liquor pH. Amino silicone emulsions are more stable on the slightly acid side; alkali carry-over both strains the emulsion and speeds the yellowing.

How does a hydrophilic silicone work?

A conventional amino silicone repels water. On towelling, socks, underwear and sportswear, a loss of absorbency is not acceptable. In hydrophilic grades, polyether blocks are built onto the silicone chain; these blocks are compatible with water, so the film stays wettable and a drop sinks in.

The cost is paid in the handle. A fully hydrophilic silicone leaves a less slippery, drier handle than a standard amino silicone at the same dosage. When the recipe is set, the absorbency target and the handle target are discussed together.

Where does micro silicone show best?

The effect reads more clearly on knits than on wovens; the loop structure is free to move, so the slip the silicone brings shows in the handle straight away. On viscose and modal a micro silicone adds softness without flattening the natural drape. On a densely woven cotton gabardine it will not carry the job alone, and the recipe is usually built together with a macro grade or a polyethylene emulsion.

Synthetics behave differently. Polyester and polyamide offer little charge for the amino group to anchor to, so the same dosage is less durable there than on cotton.

Why does the emulsion break in exhaust?

In jet and overflow machines the emulsion meets high shear, pump pressure and a hot bath. When it breaks, silicone oil separates out and leaves spotting that rinsing will not remove. The name of the DK HYDROSIL JET series points at this application; its working conditions are given on the product pages: pending from the client.

Two habits prevent most of the spotting. The product is never dropped into the machine as a concentrate; it is diluted in warm water and fed under agitation. Heavy electrolyte and alkali carry-over from the previous step is drained as well, because salt breaks the emulsion.

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