Designing the wash for effective stain removal

Staining and soiling can be defined as “matter out of place” – make-up on a pillow or wine on a table cloth, for example.

Different types of soiling will behave very differently during the wash process. For example, sugar and salt will be readily dissolved in plain cold water without the need to add any chemicals but oily, greasy soiling needs detergents and alkali to emulsify it.

If these chemicals are not used then oil and grease marks will cling steadfastly to the fabric regardless of the vigour of the mechanical action and the temperature of the water.

To illustrate this, try washing oily or greasy hands under hot or cold water without using any soap. All that will happen is that the oil or grease will spread evenly over the hands.

The types of soiling that leave stains fall into different categories and each needs a particular set of conditions for efficient removal from the fabric.

The main categories are:

Water soluble stains such as sugar and salt;

Oily, greasy soiling such as sweat, oils, creams and topical skin preparations;

Proteins such as egg, albumen or milk;

Particulate soiling, such as household dust, smoke or sand;

Vegetable dyes such as wine, fruit juices and beetroot;

Mineral/metallic soiling such as aluminium or rust marks.

There are other soiling/staining types such as mildew or dye transfer/colour mark-off but these are generally grouped as “acquired” soiling/staining and would not normally occur as a result of normal use (or abuse) by the customer.

The final consideration is the type of fabric that has been soiled or stained as this will also dictate the type of process and chemicals to be used. The aim is to remove the soiling/staining ideally without any damage to the fabric or at least only the minimum.

For example, 100% cottons are relatively unaffected by high levels of alkali, raised wash temperatures or even sudden changes in wash temperature. However, polyester and polyester-cotton blends can be seriously damaged by sudden wash temperature changes or by alkalis with an excessive pH such as caustic soda.

Many animal fibres such as wool, silk and certain man-made fibres will be damaged by even small amounts of alkali or by using wash temperatures above 40C.

So, having identified the type of soiling and fabric the next step is to design the wash process to achieve the correct level of stain/soil removal so that the work is bright, white and stain-free when it is returned to the customer.

Stains often have a mix of soils. A cup of tea contains tannin (a vegetable dye), milk (which contains both protein and fats) and possibly sugar.

The wash process must be designed to meet the requirements of each soiling type. For example, if an egg (protein) is dropped into hot water it will very quickly “cook” and the watery liquid part will turn solid and appear white.

So if protein soiling or staining matter is exposed to high temperatures in the initial stages of the wash process, the protein will very quickly “cook” and hard stains may form on the fabric.

At the start of the process it is essential to keep the temperature below 39C for at least 4 – 5 minutes after the wash dip has been achieved. This creates the right environment for providing the maximum levels of mechanical action to break-up the particulate soiling and remove the maximum amount of debris and protein. This assumes that the dip level is correct and that the degree of loading is right for the washer.

Using a high wash temperature during the early stage of the wash process will lead to the formation of stains that may be difficult, or even impossible, to remove at a later stage in the process. This applies especially to protein soiling such as blood.

If the first stage is carried out at the right temperature and for the right length of time, the temperature can then be raised to start removing the oils and fats on the fabric. At this point the process requires both maximum levels of alkalinity and the highest wash temperature. The levels of alkalinity will be largely dictated by both the level of soiling and by the type of fabric being handled.

If the process is not sufficiently alkaline, the detergent will not have sufficient suspending power so as soon as the grease and oils start to be emulsified, they will drop out of solution. So what was originally a small localised area of grease or oil will be redistributed right across the fabric so that the work comes out of the washer an even shade of grey.

Polyester-cotton blends in particular need a process that is sufficiently alkaline to ensure good suspension. Polyester has a special affinity for oil and will rapidly turn grey if oily soiling is not quickly removed and held in suspension. Once polyester has turned grey it is almost impossible to reverse the result.

Some types of soiling simply cannot be removed as a result of normal washing methods as described above. For example, dried-in tea, coffee, wine and fruit juices need to be de-natured as detergency alone is not sufficient.

This means that some form of bleaching is required. If sodium hypochlorite is used, then ideally the bleaching should take place during the first rinse.

Other bleaches that have a less damaging effect on cotton, such as hydrogen peroxide or peracetic acid, can also be used for denaturing. At the concentrations used in the laundry these only start to work once the temperature is over 60C so they would normally be applied during the main wash, when the temperature is raised. Both of these bleaches are liquid, which makes them much easier to dose automatically into the wash process. However, sodium percarbonate, which comes in powder or tablet form, is a much safer bleach and causes much less fabric damage.

Using the correct wash process and chemicals will eliminate most of the common staining and soiling. Residual staining is often a sign that the wash process is not right and needs to be checked.

Still some stains cannot be removed just by washing and these require special treatment. Rust is one such and it will only be removed by treating with oxalic or hydrofluoric acid. Similarly, washroom mud where an item has been dropped onto a wet, dirty floor will seldom wash out from the fabric and this also needs a specific special treatment.