Material solutions

Selecting the essential ingredients

1 August 2008



Richard Neale looks at some at the essential laundry chemical ingredients which combine to produce a good stain-free result and how each contributes to final quality


The laundry chemical supplier may deserve much of the credit for delivering good quality, stain-free results. However, they frequently receive little more than criticism for every complaint and for the cost of the product.

The days when the knee-jerk reaction to residual staining was to increase the bleach dosage are long gone. In the current competitive market, the first step is a re-wash analysis of residual stain types followed by a careful check of the detergent ingredients and wash chemistry to determine the correct solution.

Detergent suppliers that have this knowledge and skill are a valuable resource and the laundry should recognise this.

Extensive chemical knowledge is necessary both to formulate a detergent and to advise launderers of the best one to use.

While there is no such thing as a perfect detergent blend, there is certainly an optimum choice for each user.

Detergent blends may include a number of different ingredients.

Surfactant: This is the ingredient that makes the water wet the cloth and more importantly the stain itself. It is essential to soften protein stains quickly in the low-temperature pre-wash, so that they wash off in the high temperature main-wash. By lowering the surface tension, the surfactant helps the water to take the chemistry to the staining and soiling to deliver a clean product within a reasonable stage time.

The simplest surfactants are used in washing up liquid, but more sophistication is needed in commercial laundering to avoid foaming in the machine and at the effluent treatment plant.

Alkali: This provides lots of hydroxyl ions in the wash liquor to target skin sebum, perspiration, urine, faeces and many foodstuffs with an “animal” ingredient (such as cheese sauce and fish oils).

Alkalis are aggressive and for this reason strong detergents are labelled as corrosive rather than irritant.

The most searching detergents for restaurant work tend to contain lots of sodium metasilicate, which works more effectively than the cheaper sodium carbonate or sodium hydroxide.

Optical brightening agents (OBAs) or fluorescent whitening agents (FWAs): These are “clever” chemicals. When they are subjected to light from the (invisible) ultraviolet end of the spectrum for natural daylight, they change the wavelength of the ultraviolet rays into the visible spectrum, making the sheet or napkin look twice as white. Although very expensive, they are usually needed only as a fraction of one per cent of the detergent blend. The best OBAs will create an intense pure white, whereas others produce a blue-white or a warm-white (which is slightly pink).

Most detergent OBAs bond only to cotton and natural fibres but it is possible to have one or two which will also enhance polyester. These are becoming very important with the recent moves to polyester-cotton blends for rental sheeting.

New fabric carries its own OBAs which are often destroyed or removed in multiple washing (especially if this involves multiple bleaching). The ones lost from the cotton are replaced by the OBA from the detergent and after five or six washes (as the OBA builds up on the cloth surface) the linen is often brighter and whiter than it was originally.

Polyester may contain OBAs dispersed throughout the plastic fibres and these are protected from damage until the plastic surface becomes roughened. This can make the polyester fabric look irreversibly greyer, which is why older polyester-cotton food industry white coats usually have a much poorer colour than pure cotton ones.

Suspending agent: The soiling washed off the textile usually has a natural affinity for the textile and is immediately attracted back to it by strong electro-chemical forces. If it is allowed to go back onto the fabric, the thin layer of redeposition causes the cloth to take on a greyish tone that can take many washes to reverse.

The suspending agent in the detergent is designed to wrap around the tiny micelles of soiling to neutralise any electro-chemical charge and physically prevent redeposition and consequent greying. There are several types of suspending agent and their effectiveness depends on type and concentration. They include sodium carboxy-methyl-cellulose (CMC) and sodium tri-poly-phosphate (STPP) amongst others.

Changes in formulations may be driven by the reluctance of many water companies to continue to accept phosphate-based suspending agents such as STPP.

This may lead to more greying problems, but launderers should remember that even the best suspending agents cannot hold soiling in suspension for more than fifteen minutes at most and this sets the maximum time for the hot wash.

Hydrogen peroxide generator: Hydrogen peroxide is a very effective oxidising bleach (for vegetable dyes such as coffee and red wine) but it is not stable enough to include in a liquid detergent and it cannot be blended into a powdered one. Many suppliers use sodium perborate or sodium percarbonate in the mix. These are powders which break down to generate hydrogen peroxide in the hot wash itself.

Enzyme: Enzymes are chemicals (some of which are found in the human stomach) that progressively break down or digest protein soiling and staining from blood, perspiration and other human body fluids. They are excellent for heavy restaurant soiling and healthcare work because they will digest aged soiling and staining. They work best at 40 – 60C and they take time to work completely.

Sequestering agent: The best laundries use softened water but where this is not immediately possible, the use of a built detergent containing a sequestering agent will capture the hardness ions (calcium and magnesium ions for example) and so avoid greying and excessive detergent use.

Chelating agent: Iron continues to be an intermittent problem in many laundries, accelerating fabric damage and causing greying, yellowing and rust speckles. Detergents containing chelating agents are designed to capture iron and render it harmless, dramatically improving quality and textile life.

The ingredients listed above are those that a laundry might find in the detergent it is buying. If a detergent is not working, then the laundry might be buying the wrong one or it might not be dosing correctly or it might be using wash times and temperatures that are not getting the best from the product. The problems should be discussed with the chemicals supplier.

Dosed separately

There are also several chemicals which are dosed separately from the main detergent. These include:

Hydrogen peroxide: This is a liquid bleach designed to work in the hot wash at temperatures above 60C.

If it gets into the pre-wash, this can slow down protein stain removal. Hydrogen peroxide can decompose explosively if stored incorrectly or if it is mixed accidentally with sodium hypochlorite bleach.

Sodium hypochlorite: This is a liquid bleach but it is designed to work at temperatures below 60C, so it is ideal for stain removal in the first rinse where it targets those stains not removed by the wash. Used correctly, sodium hypochlorite and hydrogen peroxide both produce an acceptably low level of chemical damage. Used incorrectly (at higher temperatures), sodium hypochlorite causes excessive damage to cotton and this is accelerated further by the presence of iron.

Sodium dithionite: This is a reducing bleach powder which works by removing a molecule of oxygen from the staining.

It often works where oxidising bleaches (such as hydrogen peroxide and sodium hypochlorite) fail, making it ideal for reversing overall tinting of a batch of white goods by accidental inclusion of a coloured item in the load.

Emulsifier: This is a liquid added to the first wash of a batch of heavily soiled work to help to solubilise the oils, greases and fats more quickly and at lower temperature.

Oxalic acid: This is supplied in crystalline form and is used to remove iron discolouration (including rust speckles) from otherwise serviceable goods. It is also used to remove the brown ring residues from old blood stains, (which are iron oxide from the haemoglobin in the original blood).

Hydrofluoric acid: This is a liquid solution of hydrogen fluoride in water. It is a very powerful chemical kept in plastic bottles because it will dissolve glass ones. It is usually used for removing the odd rust spot, after which the article must be washed immediately before the fabric dissolves to form a hole. Stringent safety conditions apply to its storage and use.




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