Which is the ‘best’ detergent?
Why are some detergents more expensive than others?
Why can some launderers remove stains that defeat your team?
Why do your towels gradually turn grey?
Can rust marks be removed?
This month we look at the latest laundry chemistry and how to make this work for you!
Saponification and emulsification
Laundry detergents are generally alkaline: they generate lots of hydroxyl (OH-) ions, which in combination with heat and mechanical action will react with fatty soiling and staining (from both foodstuffs and human skin oils).
This reaction is termed ‘saponification’ because it converts any insoluble fat into a soluble soap, so that it comes away and gets flushed to drain. Oils, greases and fats can also be solubilised at lower temperatures if the chemicals supplier adds a tiny dose of an ‘emulsifier’. This normally goes into the pre-wash, from where it is carried forward to act in the main wash as well.
Small amounts of emulsifier can work miracles with wash quality, avoiding the need to overdose with detergent to clear fatty staining. They are particularly useful when laundering polyester and blends containing this fibre, because oils, fats and greases tend to cling tenaciously to synthetics, which sometimes makes stain and soil removal from polyester table linen surprisingly difficult.
Even better results are obtained by matching the HLB (hydrophilic-lipophilic balance) of the emulsifier to that of the oils to be removed. This is particularly important when removing spa oils from towels and sheets. Premium emulsifiers span a range of HLB values, giving good results for a wide variety of stain types.
Launderers used to rely heavily on oxidising bleaches such as sodium hypochlorite for stain removal. With an increasing demand for lower temperature washing the bleaching agents and supporting detergent systems now being used are evolving and worthy of discussions with your detergent suppliers.
A “gentle” oxidising bleach, such hydrogen peroxide solution or sodium percarbonate powder is still widely used for removing vegetable dye stains from tea, coffee, red wine, beetroot and blackcurrant – indeed for any plant dye.
In order to remove food fats, food oils and human skin sebum from one-night hotel sheets, the first priority is to soften these stains in the pre-wash (a minimum of four minutes below 40C), so that they come away easily in the main wash.
The effectiveness of this can then be enhanced using the appropriate emulsifier, which often enables lower detergent dosage and lower main wash temperatures. Launderers often make the mistake of trying to wash out stains in a one-wash, high-temperature process, which often results in severe stain-setting of proteins as soon as the temperature exceeds 40C.
If time and water usage are critical, it makes more sense to convert this to a stepped wash, in which the temperature rise is held just below 40C for 4 – 5 minutes before going on up to main wash temperature.
Machines that incorporate Xeros Technologies, report a reduction of over 50% in water and energy consumption, by using XOrbsTM to displace half of the wash water in the drum, making this extremely attractive in terms of cost reduction (with no reduction in wash quality). This is another triumph for human innovation!
Difficult stains – rust, aluminium, tinting
Metal marking used to be regarded as staining which it was impossible to remove, but that has changed.
There should now be no need to scrap quantities of sheets or towels which have been stored outdoors. If rust-marked linen is collected until there is enough for a full washer-extractor load, then this can be recovered using a dedicated process. Most leading detergent suppliers can now offer a recovery system, which can be safely flushed to drain.
The same applies to aluminium marks picked up from kitchenware and misuse during use. This can be removed using a dedicated high-alkali process, based on sodium hydroxide or sodium metasilicate. Again, the aluminium-marked stock should be classified together until there is enough for a washer-extractor load. Both of these recovery processes will reduce the life of the textiles slightly, which is why they should not be used on a regular basis, but only for the stains in question.
If a coloured pen, which has been missed in a pocket search, accidentally tints an entire load of whitework, the replacement cost for the now unusable textiles can be considerable. It is often found that normal oxidising bleaches (even sodium hypochlorite) do not remove the unsightly tint. It is then worth trying a reducing bleach such as one based on sodium dithionite crystals. Most leading suppliers of laundry chemicals can offer this process, but it is important to follow their instructions carefully, for safety reasons.
Suspending power – whiteness retention
Historically, low-cost, high volume laundering was often characterised by increasing greying of the circulating stock of white textiles, particularly towels and pillowcases. Greying that occurs in the wash process is usually caused not by failure to wash the soiling off the fabric, but by failure to stop soiling now in the wash liquor from re-depositing onto the clean fabric (which is caused by normal electro-chemical attraction).
Premium detergents contain adequate ‘suspending agent’ to prevent this. The suspending agent wraps around every tiny group of soiling molecules, neutralising any electro-chemical charge as well as physically preventing re-deposition.
Greying or browning localised in the central area of a pillowcase, where the sleeper’s head has been, is caused by failure to wash off the skin sebum and hair oils from the sleeper. This is cured by improving the wash process itself (by attention to the detergent dose, the emulsifier, the stage time or the temperature).
Overall greying of towels is occasionally caused by re-deposition in the wash process, but much more frequently it occurs as a result of over-drying. This is cured by setting the drying times to give around 2% residual moisture in the towels. Drying down to zero moisture results in the dry terry loops acquiring a tiny static charge as they brush against the rotating metal cage, which causes them to attract every tiny particle of dust from the drying airstream. The resultant greying is not removed completely in the next wash and the result is towels which look grey and old when they are often less than half way through their useful lives. This can best be cured by fitting automatic cycle terminators in the dryers and setting these carefully to deliver a consistent residual moisture in the dry towels.
Concentration of active ingredients
Successful laundering relies on the correct concentration of each critical chemical in the wash liquor. Performance generally improves with dosage until the optimum is reached, above which any improvement stops and sometimes causes harm. For example, overdosing with detergent can cause foaming and gall marking, whilst overdosing with bleaches can reduce textile life. Quality management relies on finding the optimum process in conjunction with the chemicals supplier and then operating with this. In order to reduce the chemicals cost, the dosage could be reduced but this carries a quality penalty. Only one washer designer has really tackled the amazing opportunity this offers.
Xeros-enabled washing machines use XOrbsTM to reduce the amount of wash water needed to make the required dip. One consequence of this is that it also reduces dramatically the dosage of the key chemicals needed, because it is the concentration of chemistry in the wash which determines the wash quality, not the absolute amount.
This offers the chance of halving the chemicals demand without any reduction in quality, making Xeros-enabled machines quite outstanding. It means that if the suggestions made here are adopted, then achieving optimum soil and stain removal at very low chemicals cost becomes possible, even for operators in the most cost-conscious of markets.
At one time, achieving assured disinfection meant ensuring the main wash maintained a minimum of 71C for a minimum of 3 minutes plus mixing time. This typically gave a 5log10 reduction in viable micro-organisms to meet the requirements of the UK National Health Service and most national healthcare standards bodies worldwide.
Most leading chemical suppliers can now achieve disinfection to the required standards at temperatures down as low as 40C and this includes control of new viruses such as SARS-CoV-1 which causes Covid-19.
Some of these processes use peracetic acid, whilst others use a variety of low temperature disinfecting agents, but all of them require careful adherence to every process parameter – there is no single magic chemical ‘bullet’!
Laundry chemistry has come a long way in the last 10 years and modern research is now having wide and far-reaching effects on quality, operating cost and productivity.
It is important that the Washhouse Supervisor and Laundry Manager have sound understanding of the vital components of a well-designed wash process.
They are vital when purchasing, using and managing effective wash processes.
Written by Steve Anderton, Director at LTC Worldwide.