Choosing a silicone softener: handle, yellowing and emulsion stability

Micro, macro, elastomeric: where does the difference come from?

All three are silicone. What separates them is the particle size of the emulsion, and therefore where the silicone ends up sitting on the fibre.

Macro-emulsions are built from large particles. They look milky white, because the particles are big enough to scatter visible light. They do not penetrate far into the yarn body and stay largely on the fibre surface and between fibres. The handle is slippery on the surface, full and bulky. That first-touch softness comes from here.

Micro-emulsions are built from much smaller particles, which is why they look translucent or clear. The particles get into the yarn body and between individual fibres. What you feel is internal rather than surface softness: silky, fluid, with good drape. The cloth reads thinner and softer, and it gains no bulk.

Elastomeric silicones are defined by structure rather than particle size. They form a crosslinked, rubber-like network on the fabric. What they add is recovery more than softness: the cloth returns to itself after being stretched, with a fuller and springier handle.

The Derin Kimya families follow that split. DK MICRO F, DK MICRO S NEW and DK MICRO S CONC are micro-emulsions. DK MACROPLUS 8020, DK SOFT MACRO, DK SOFT MACRO CONC and DK MACROSOFT 1347 sit on the macro side, while DK SOFT MACROMIX is positioned as a macro and micro blend. DK ELASTOSIL and DK ELASTOSIL 300 are the elastomeric products. Application figures are product specific: pending from the client.

What does amino content buy, and what does it cost?

Amino groups are what anchor the silicone to the fibre and orient it correctly. As amino content rises, softness rises with it and the effect survives washing better.

The cost comes from the same groups. Amino functions oxidise under heat and air on the stenter, and the fabric yellows. So the same molecule is the source of both the softness and the yellowing. The trade-off is direct and there is no way around it. There is only a place to stop.

The shade decides. On optically brightened whites and on pastels, low amino or modified types are used; the target there is keeping the whiteness, not reaching maximum softness. On dark shades the yellowing is invisible, so high amino types can be used freely.

Modified structures fill the space between the two ends. Blocking the amine or converting it to amide-type functions lowers yellowing, and softness gives a little ground in return. A product described as low yellowing is not the same as a product that is equally soft and does not yellow.

Why can a towel not take a standard amino silicone?

A silicone film orients its methyl groups outwards, and that surface repels water. What is wanted for handle is exactly the problem for absorbency.

On towelling, sportswear, diaper coverstock, wipes and medical textiles, the rate of water uptake is a specification, not a preference. A standard amino silicone ends the drop test on those articles. The picture is recognisable: the cloth is extremely soft and the water droplet sits on the surface.

Hydrophilic silicones exist for that reason. Polyether segments are built into the chain, so part of the molecule stays friendly to water and the surface stops repelling it. What you get is a usable balance between softness and absorbency. What you give up is real: hydrophilic types usually do not feel as slippery as a straight amino silicone, and their durability to washing is more limited.

DK HYDROSIL JET, DK HYDROSIL JET ECO and DK HYDROSIL JET 654 belong to this group. Which one works on a given quality is settled with a drop test; a handle approval on its own is not enough.

What problem does an elastomeric silicone solve?

The crosslinked network an elastomeric silicone forms lets the fibre move and helps it come back. In practice that pays off in three places.

The first is elastic recovery. On elastane knits the fabric returns better after stretching and growth in wear goes down. The second is dimensional behaviour: the cloth stands up rather than collapsing, and the handle reads full instead of empty. The third is sewability. With lower surface friction the needle enters more easily, needle heating and the knit damage that follows it go down, and seam puckering complaints fall back.

The curing temperature band quoted in the literature for silicone finishing on the stenter is 150 to 170 °C. That is a class range, not a product specification; Derin Kimya's own figures sit on each product page.

There are downsides. Elastomeric types do not give the silky slip of a micro-emulsion, which is why recipes combining the two are common. Film formation is also sensitive to drying and curing conditions, so when the stenter settings move, the handle moves with them.

How does an emulsion cost you a batch?

Silicone spotting is an expensive fault. It appears after drying, looks dark and oily, usually comes out only with a solvent wash or a re-emulsifying treatment, and sometimes does not come out at all.

The things that break an emulsion are a short list.

Shear. The pump and circulation in the padder trough apply continuous mechanical stress to the emulsion. On long runs it breaks and free silicone oil comes to the surface.

Water hardness and electrolyte. Hardness ions and residual salt reduce emulsion stability.

pH. Amino silicone emulsions are stable in a particular pH region. Alkali carried over from the previous step breaks that balance, which makes proper neutralisation a precondition for the softening step.

Ionic incompatibility. Amino silicones behave as weakly cationic. Put one in the same bath as an anionic finish or an anionic softener and it precipitates.

Wrong dilution. Pouring concentrate straight into the bath is the most common failure and the easiest one to avoid.

So the application sequence is fixed:

1. Confirm the cloth is neutralised and the pH is on target.
2. Dilute the concentrate in a separate vessel with cold water, stirring. Never dilute the other way round.
3. Add the diluted product to the bath slowly, with circulation running.
4. Keep the bath volume and run time in the padder trough under control; refresh the bath on long runs.
5. Check the strainer and filter on every batch. A broken emulsion shows up there first.
6. Verify the ionic character of anything being combined in the same bath before the batch, not during it.
7. Take samples from the selvedges and from folds and check them before the batch is dried.

Exhaust or pad?

Dosages do not convert between the two. On exhaust the dosage is set against fabric weight; on the pad it is set by bath concentration, and pick-up is the bridge. Change the nip pressure and the recipe changes with it.

The machinery usually settles the question: a finishing line means padding, and without one it is exhaust in the dyeing machine. The same handle target can be reached either way, but not with the same recipe.

Comparing the types

What to check before approving a softener on a new quality

1. Assess the handle on a dry sample. A decision made on wet or half-dry cloth does not hold in production.
2. Measure whiteness and shade on a cured sample. Yellowing appears after the stenter, so a sample judged before curing misleads you.
3. Run a drop test. On articles with an absorbency requirement, this comes before the handle approval, not after it.
4. Assess the handle again after washing. Durability cannot be judged from the first touch.
5. Test bath compatibility in the lab, with your own water, at your working pH and alongside every other product in the bath.
6. Check the effect on the next step. Sewing trials, and adhesion trials where printing or bonding follows, belong at this stage.
7. Write the approved conditions onto the quality card. Without nip pressure, stenter temperature and speed on record, the handle cannot be repeated.