Desizing Enzymes

Alpha-amylase breaks the starch size on the warp into water-soluble fragments and takes it off the cloth. Because it does not touch cellulose, it causes no strength loss. Derin Kimya's desizing range holds six products, in medium- and high-temperature types.

Why does size have to come off?

Before weaving, warp yarn is sized so it can stand the abrasion of the loom. On cotton wovens most of that size is starch, and it sits on the cloth as a water-insoluble film. While the film is there, neither the bleach liquor nor the dye reaches the fibre. Desizing is therefore the first step of pre-treatment, and it sets the efficiency of everything that follows.

Alpha-amylase cleaves the α-1,4 glycosidic bond in starch at random points. The long chain breaks into short, water-soluble fragments that rinse out of the cloth. Because it does not touch cellulose, it causes no strength loss, and that is what separates it from caustic or oxidative desizing.

How does enzymatic desizing compare with the alternatives?

Synthetic sizes (PVA, acrylate, CMC) are not removed by enzyme; they come off with hot water and a suitable washing agent. Where mixed sizes are used, both routes have to be planned together.

High-temperature or medium-temperature amylase?

The machine decides. On a continuous range the cloth enters the steamer hot and the dwell time is limited, which calls for a high-temperature amylase. In exhaust and jigger work the temperature is lower and the time longer, so medium-temperature types will do.

The general working window quoted in the literature for the alpha-amylase class is pH 5.5–7.0, with temperature ranging from around 60 °C to above 100 °C depending on type. That is a class range, not a product specification. Derin Kimya's own figures are given on each product page: pending from the client.

Wide-window types are formulated for mills that want one product to cover several machines, and they cut the number of items on the recipe sheet.

How do you know the size is off?

The standard method is the TEGEWA violet scale. A drop of iodine solution is put on the cloth; any starch left gives a blue-violet colour with the iodine. The colour is matched against the steps of the scale and the degree of desizing is read off. For reactive dyeing the upper steps are normally the target, because residual starch shows up as a light stain.

The test can be run on a wet sample without drying the cloth. One reading at the start of a shift costs less than scrapping a whole batch after dyeing.

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