Modern solutions to the complex challenge of stains

5 February 2014



The types of stains that now confront launderers and rental operators have led to a radical re-think of the wash process. Richard Neale looks at just some of the current problems and suggests some tried and tested solutions


The types of stains that now confront the launderer and rental operator have changed significantly during the last twenty years.
Some of these changes have occurred because of developments in the washing equipment. Far more have arisen because the water has changed, both in temperature (with the advent of heat recovery from hot effluent) and in flow-rate (falling from a typical 8litre/kg down to as low as 1.2 litre/kg now).
The results of these changes have meant a radical re-think of the wash process. To take one example, washing now continues right through the rinse zone in systems using peracetic acid neutralisation.
Detergent suppliers have had to respond to the problems associated with warm rinse water in tunnel washers. Complaints of poor stain removal can occur three months after the heat recovery system was commissioned. By this time there may be one or two un-removed stains on every item in circulation.
This month's article examines some of the current problems and suggests some tried and tested solutions, together with a few problems for which the jury is still out.

Stains caused by cosmetic dyes
The use of rental towels by spas and hotels with spa treatments has led to complaints following poor removal of brown marks from white towels.
These marks do not succumb to oxidising bleaches such as sodium hypochlorite or hydrogen peroxide.
Even a reducing bleach such as sodium dithionite can fail to remove many of these. However this should always be tried as it will remove 90% of stains that hypochlorite does not touch.
If a stain cannot be removed either by oxidation or reduction, then it is almost certainly a dye from a self-tanning lotion or other cosmetic preparation. The very few stains that survive are genuinely irremovable and the only solution is to scrap the towel and charge the customer for the replacement.

Removing oily staining
In many circulating rental stocks the central area of the pillowcases is frequently a much poorer colour than the sheets. Often this central area looks brown in comparison with the pillowcase edges.
This is partly because many launderers tend to use the same process for the pillowcases as for the sheets, without recognising that the sleeper's head moves over the small area of the pillowcase during the night, transferring skin sebum and hair oils onto a small part of the fabric.
It is not reasonable to expect a wash process designed for a sheet to cope with this concentration of soiling on a pillowcase. If this is not addressed correctly, then after a year the pillowcase acquires a brown circular patch in the centre that is irrecoverable.
The solution is to increase the oil-removing power of the pillowcase wash by using an emulsifier at low dosage.
This may need to be augmented by keeping the pre-wash temperature below 40C, so that at this stage the proteins in the skin and hair oils are softened rather than set.
Similarly oily, greasy staining on chefs' trousers frequently becomes a shade darker over time, acquiring a rancid odour at the same time. This can usually be completely removed with a high alkali wash with sufficient detergent plus an emulsifier to break down the oil and grease.
Redeposition of oily soiling onto engineers' overalls can only be prevented with sufficient suspending agent, either by increasing the detergent dose or by the use of a better detergent with more suspending power built in.

Black "snake bite" marks
The cause of these black marks has generated much debate, with the Textile Services Association already convening a working group to look at this problem. There is evidence, from Europe in particular, that suggests that certain components of washing equipment, made from various grades of rubber, are a possible cause.
The best components probably use one of the higher grades of EPDM rubber because of its excellent resistance to the strong alkalis used in the best detergents. These have worked well for many years.
However, modern wash systems use acid sours, acid antichlors and acid neutralisation in the final compartments of the tunnel washer. These are designed to produce neutrality in the last compartment but this is by no means an exact science.
If the acid component is slightly over-dosed, then the liquor goes to the acid side of neutral (below pH7.0) and the rubber might be far less resistant to this than it is to high alkalinity. As a result equipment seals can come under attack after two or three years producing a black tarry breakdown.
There is at present a spate of black mark problems across the rental industry, characterised by twin (occasionally triple) marks that look rather like a snake bite. These might be caused by the breakdown of rubber seals under conditions which are occasionally acid.
There is no known means of recovering stock damaged in this way. The best advice is to prevent any possibility of the formation of these marks through acid attack by controlling the pH of the final compartment and by changing seals at the manufacturer's recommended intervals (probably annually).
Control of pH is needed, because the actual pH in the final compartment will vary with the bone-dry weight of the batch, which inevitably varies from batch to batch. Because pH is difficult to control, the most successful systems use measuring probes, that allow a laundry engineer to investigate if they are giving different readings.

Hotel cleaning chemicals
Hand towels and pillowcases make very handy cleaning cloths for the room service staff, who may frequently use them for wiping down bathroom ceramics and mirrors.
Ceramic cleaners tend to be very acidic and they will quickly strip the pile off one side of a terry towel after a single misuse. Mirror cleaners contain a wide variety of contaminants, some of which leave permanent marks. Those that contain metallic compounds can usually be seen very clearly under ultraviolet light. Damage from ceramic cleaners is terminal and the towels with bald areas should be scrapped and the customer charged for the replacements.
If a cage of soiled towels is checked with the appropriate abuse-indicator, it will often be found that 30 - 40% of the hand towels are affected in this way.
To detect abuse, it is best to use a UV light, when the presence of any metal salts will show up as dark areas of staining. These need to be discussed in a tough fashion with the user.
Premature replacement of linen takes away the rental profit and more, so there is no point in worrying about upsetting the customer. These customers are not wanted at any price.
Napkins in particular are often used for cutlery cleaning, which creates black areas of marking that are very distinctive. These are often exacerbated by use of the same cloths for cleaning the kitchen work-surfaces.
Once these abuses have been addressed at source it is often possible to recover some of the damaged stock with a good recovery process.
Dark protein staining from a kitchen wipe-down will often succumb to a very high alkali wash for 15 minutes at 85C. This same high temperature, high alkali wash will also remove most of the ingrained yellow protein soiling and staining acquired by chefs' wear in normal use.
Metallic stains (from cutlery cleaning or rusty rainwater contamination) will come off with an oxalic acid wash (no detergent, just one bath with oxalic acid crystals for 10 minutes at 80C, followed by three rinses).

Mildew stains
Mildew is a naturally occurring fungus, which grows on the cellulose of the cotton. It plants "roots" deep in the yarns and does not succumb quickly to stain removal. Although strong bleaching will sometimes improve very fresh mildew, it will not take out growth that has had a few days to establish itself. The result is the familiar black, blue, green and occasionally red or yellow spots.
If this is a familiar and recurrent problem, then the first step to solving it is to improve the storage conditions for the soiled work, to eliminate wet, dark and cold conditions under which many varieties of mildew thrive.
Some types of mildew will also be encouraged to grow in warm and humid conditions. Storage is usually under the control of the user, so if mildew develops on a regular basis and ruins stock, then the user should be charged.
To recover mildew-damaged stock, it may well prove much more effective to soak the textiles overnight in a very weak solution of sodium hypochlorite (around 50 parts per million) than to risk a short bleach rinse at high concentration. The long soak will cause less fabric damage and be more effective at removing the deepest mildew discolouration.



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