Effective stain removal at affordable cost

In the spectrum of customer complaints, sending a hotel or restaurant items which are still stained is guaranteed to send housekeepers or restaurant managers into a frenzy. The laundry is perceived as being staffed by skilled professionals, for whom removing every stain should be ‘a walk in the park’.

Here we review the common errors in effective stain removal and suggest simple steps to get this right. More importantly, we indicate the costs of not doing it properly, which can (for large circulating stocks) run into large and unnecessary losses, every year.

Stain identi­cation

If you are faced with an increase in washed items which emerge still-stained, rather than leaping for the bleach or increasing your rewash capacity (both which will raise your costs), it usually makes sense to examine some of the surviving marks under ultraviolet light. Protein stains will fluoresce towards pink, whereas tannin stains will not change much if at all. Metal marks from rust, old blood, aluminium cooking vessels and so on will fluoresce very distinctively towards black. Overall tinting, caused by use of an inappropriate optical brightener in manufacture, will give an enhanced tint.

Once you have identified which group of stains is giving you the main problem, you can then target the correct part of the laundering process and tweak this with confidence.

Tannin stains

Tannin and similar vegetable dyes feature in a great many heavily coloured stains, but they can be removed without damaging their textile host. They come from vegetable sources, such as beetroot, blackcurrant, red wine, grass and many curry spices – indeed, anything which once grew in the ground.

They are decoloured (and made invisible) by mild oxidation using one of a variety of bleaches. Dilute solutions of sodium hypochlorite are still preferred in many areas, because these are inexpensive, but many regions now demand banning of this chemical (because it can cause eutrophication of long, slow-flowing rivers, with severe environmental effects). It could be replaced by hydrogen peroxide or other similar chemical, which are just as effective as hypochlorite on vegetable dyes.

These oxidising agents will degrade cotton only slightly if used correctly, which reduces textile life by a negligible amount. The launderer should still get 200 wash and use cycles, unless the items disappear earlier or other reasons.

The danger with sodium hypochlorite is twofold – some launderers use this at too high a strength, to try to burn off protein stains chemically, which can be a very expensive mistake (because this can reduce textile life down to well under 100 wash and use cycles). Other systems (especially those using tunnel washers) allow recycling of excess sodium hypochlorite into the pre-wash or the hot wash. This has a devastating effect on cotton life and can reduce this to below 50 wash and use cycles!

Launderers of hotel linen are encountering chlorhexidine staining, which is now used as a disinfectant in a wide range of retail skin treatments. This is colourless until it comes into contact with sodium hypochlorite, which reacts with it to form an indelible yellow-brown dye! This type of stain is avoided entirely by using hydrogen peroxide for bleaching!

In addition to the two chemicals mentioned, speak with your chemical supplier to get a full understanding of the alternatives.

Protein stains

No launderer should ever rely on oxidation by a bleach to take out difficult protein stains. These usually come from a living animal or human body and include all human body fluids such as blood, urine, faeces, perspiration, semen, hair oils and skin sebum. They also include greasy cooking fats, gravy, and some vegetable oils.

Protein stains need to be softened by a pre-wash which runs for at least four minutes below 40C. They will then come away easily in the hot wash, with a combination of temperature, detergency and mechanical action. Failure to ensure correct pre-wash conditions will result in partial or total setting of the proteins, making them much more difficult to remove in the hot wash. This is the origin of many “very stubborn stains” and the solution is to check the pre-wash time and temperature and get these right.

Poor removal of protein stains is becoming more of a problem with the current essential trend to cool washing, with ‘hot wash’ temperatures commonly reducing to around 40C. This is being addressed by detergent suppliers using chemical emulsification to disperse softened proteins.

Some modern chemical systems also use low-temperature activators to release hydrogen peroxide directly into the wash, from suitable chemicals such as sodium percarbonate to achieve tannin stain removal without resorting to sodium hypochlorite. This often improves linen life as well.

It is important to note that compound stains, containing both tannin and protein fats or oils, will only come away completely if the protein is removed first, so that the system can then oxidise the tannin stains.

Thus, particularly in CBTW’s, modern chemical systems may include the addition of Alkali at the pre-wash compartments of the CBTW. If controlled effectively, this assists in offsetting the effects of the heat contained in the CBTW’s recycled water on the protein soiling allowing the prewash to operate at temperatures slightly over 40’C without setting the protein staining.

Dye bleeds

A loose marker pen in an overall pocket can tint an entire load of white polycotton garments. A tiny amount of ink goes a very long way! This is rarely removable by oxidation and it is unwise to try massive amounts of sodium hypochlorite to prove this. The polyester might survive but the cotton will rapidly disappear. It is often worth trying a reducing agent such as sodium dithionite to recover the damaged work, but be sure to check the safety instructions with the supplier, as the process will generate an odour of bad eggs. This is potentially poisonous and calls for good ventilation and a deserted workroom.

Spa treatments

Spa oils are notorious for two reasons – firstly they can be very difficult to remove resulting in residual odours. This is because not all emulsifiers work on several types of spa oil – they need one with an appropriate HLB (hydrophilic-lipophilic balance) value. This leads to the second problem: the unremoved oils slowly degrade, giving rise to acidic by-products, which rot cotton and lead to early holes and tears. There is a third issue as well: unremoved oils can ignite during tumble drying (or later in the warm, finished goods pile), making them a source of spontaneous ignition and serious fires.

Spa oils, and the odour and yellowness they produce, can be removed quite easily simply by using the correct emulsifier. The way to check that this is happening is simply to sniff each batch of spa towels as they come out of the dryer. If there is any trace of the scent of these essential oils (or their rancid breakdown products) then take remedial action straight away!

Optical brighteners

If you are unfortunate enough to receive batches of textiles with a background tint (which could be red, yellow, blue or green) from new, then you have an immediate customer problem. Inexpensive brighteners (often those intended for the paper industry) can react with the optical brightener in good quality laundry detergents to produce a tint, sometimes where nothing could be seen before the first wash. If you want to rectify this and the goods are 100% cotton, then rather than returning the goods to the supplier, you could try a normal dose of sodium hypochlorite in a test load in a small washer extractor. Otherwise, return is the best option, because the tinting will probably survive for the first twenty washes or so.

Iron marks

Iron is an important constituent of blood (in the haemoglobin), which is why old blood stains frequently develop a rusty brown ring around them. Whilst fresh blood is readily removed (provided the pre-wash conditions are correct), rusty brown rings are near indelible. They can be removed using a special treatment in a washer extractor. The process involves the addition of oxalic acid crystals to the initial hot treatment stage (which dissolves the iron oxide in the rusty ring as iron oxalate), followed by three rinses. It is important not to add detergent to the treatment stage (because the alkali in this neutralises the oxalic acid and nothing happens). The best procedure is to accumulate rust marked stock until you have a full washer-extractor load, then put it through the treatment process, followed by a normal wash to ensure the treatment is completely removed. This procedure also minimises the slight damage which oxalic acid can cause to the machine and to the cotton in the textiles.

Aluminium stains

Modern kitchens often use aluminium for cooking vessels and other surfaces. If textiles are used to wipe these, they can accumulate dark unsightly marks which a wash process cannot remove. The most successful recovery processes for aluminium marking tend to use sodium hydroxide crystals in a special recovery wash. This can also include detergent, unlike the process for iron removal. The sodium hydroxide dissolves the aluminium to form aluminium hydroxide, which goes into the wash liquor and is flushed to drain in the rinses.

You should contact your detergent supplier for the chemicals for both iron and aluminium removal and for the process details for your equipment.

Mildew

Mildew grows on the textile from vegetable spores that create vivid dyes, typically black , red, green and blue. These dyes generally do not wash out but the mildew spore can be killed effectively and the dyes can be decoloured (with the occasional exception of the black) using a very dilute solution of sodium hypochlorite (about the same dosage as might be used for bleaching with hypochlorite). If the process is not completely successful, don’t increase the hypochlorite dosage (because this will risk rotting the cotton); simply increase the stage time, by several fold if necessary. Mildew spores can grow deep into the cotton fibre and removal might take many minutes. Finish the process with three rinses and full extract.

Conclusion

Stain removal relies mainly on correct processing and good process control, but professional launderers are now able to do a much better job using the techniques described. Working with the advice here and/or liaising with your chemical suppliers can lead to improvements in customer satisfaction without significant increase in laundering costs. ­