Tackling stains effectively to reduce re-wash and cut costs1 April 2016
Richard Neale of LTC Worldwide argues that tackling difficult stains effectively first time can minimise re-wash, improve margins and cut costs
Residual staining is a serious problem for the laundry/textile rental industry and can have a damaging effect on costs. Margins are so slim in many sub-sectors that removing stains first time can make the difference between profit and loss.
The knee-jerk reaction in many plants is to increase bleach dosages without any attempt to find the cause of the problem and the most cost-effective solution.
To reduce residual staining, launderers need to be aware of the different stain types and have an armoury of techniques for removal. In this way it is usually possible to solve stain problems, minimise re-wash and extend linen life.
Sometimes the solution requires a different approach, sometimes it relies on traditional methods that are rarely used now but should be revived.
Failure to tackle residual stains effectively is costly. A 5% increase in the re-wash will raise energy and water bills by the same amount. Further, if that re-wash only works half the time, the stock replacement costs rise by 2½%. The sums involved are huge and unless problems with residual staining are solved, costs will continue to rise.
Vegetable dye stains include tea, coffee, red wine, blackcurrant and beetroot. These might look horrific on table linen but in most cases they can be readily removed by using an oxidising bleach such as sodium hypochlorite. Hydrogen peroxide is also effective on vegetable stains but sodium hypochlorite has the advantage of being able to reduce some protein stains as well and is therefore known as "the better bleach".
The main cases in which sodium hypochlorite will not work are those where vegetable dye is bound to the fabric by set protein as the protein prevents the hypochlorite from tackling the vegetable dye.
Protein stains come from human body fluids, meat juices and dairy products. They need to be softened in a pre-wash that runs for at least four minutes at a temperature below 40C.
Protein stains will "set" once the temperature rises above 40C and are then much more difficult to remove.
This can be a serious problem on many tunnel washer installations, where it can be difficult to control pre-wash temperatures, if local water temperatures are high or if heat recycling systems are in place.
If yellow-brown staining remains or appears unexpectedly after finishing it should be examined under UV light. If it fluoresces towards coral pink, then this is probably a protein stain and will need a re-wash process, specifically designed for this purpose.
Grey marks and rusty brown marks, which fluoresce towards black under ultraviolet light cannot be washed out because they contain metal ions.
Instead they must be treated in a special washer-extractor process with oxalic acid crystals.
Rust marks (iron oxide) fall into this category but they will come away completely if they are correctly treated. The best practice here is to put rust-marked stock to one side until there is enough for a full washer-extractor load.
Grey marks may well appear on napkins or pillowcase as a result of these items being wrongly used to polish knives. The dark grey lines that characterise this staining will fluoresce to an intense black under UV light.
Black marks - membrane press traps: If the press basket is even slightly misshapen or if the membrane itself is damaged, then rubber oil from the membrane will mark off onto the sheets that are in contact with the membrane.
Black membranes are typically made from recovered rubber crumb blended with rubber oil and re-vulcanised. The rubber oil and the carbon black reinforcement in the rubber combine to cause this type of black mark.
A press basket may lose its circular shape when the press fails to discharge one cheese before forming another and jams as a result.
Such jams, and the black marks they leave, can be avoided by bleeding out all air from the membrane when setting the profile and by checking periodically that air has not leaked back in past the sealing washer on the bleed nipple.
The black marks caused by a damaged membrane press can be recognised by their slug-like shape and by localised tears that are curved and cross the lines of warp and weft.
Black marks - seal degradation: These marks look like "snake bites" and consist of two small, circular black dots 1 - 2mm across. They occur when the seal between two tunnel washer compartments starts to break-up and as a result a small crumb of sticky rubber becomes trapped in a fold of fabric, pressing firmly into both sides.
The degradation is frequently caused by acid conditions in one chamber of the tunnel washer.
The standard seal material is EPDM rubber, which will resist alkaline attack very well and can also tolerate low residual concentrations of sodium hypochlorite bleach. However, this rubber is far less resistant to acid and it is this that breaks down the rubber's molecular structure.
Increasingly modern wash chemistry relies on using an acid to neutralise residual alkaline as this saves water.
Rinsing out alkaline and other residues can take 7litres of fresh water per kilogram washed, whereas neutralisation uses less than 5litres/kg and in some cases below 2litres.
Controlling the acidity/alkalinity in the final two compartments can be quite difficult as automatic pH controllers are notoriously difficult to maintain and calibrate. This factor together with variable load weights means that occasional acidity is difficult to avoid and will lead to premature seal failure and therefore to black marks.
However, the latest seals have been designed to overcome acid degradation.
Black marks from feeder and folder traps: These occur when textiles go astray and get caught in feeder or folder rolls, belts or bearings. Once membrane press problems have been ruled out, the presence of oil and grime near the marks identifies them as resulting from feeder or folder traps.
Floor marks: If linen is dropped or trailed along the floor, concrete dust and floor grime gets embedded into the interstices of the weave. Removing this is exceptionally difficult, especially when the marking occurs on "one-night" hotel sheets that would normally need only a mild process.
While there are processes that will remove floor marks, these will shorten the linen life. The best solution is to stop linen getting marked in this way.
The laundry manager and production managers should complain so loudly if even a single item gets dropped or trailed, that staff will make every effort to avoid such mishaps.
Once carelessness in the laundry has been eliminated, the managers can then turn their attention to problems caused by customers. Check stock from one customer at 100% level to see how much of their incoming stock has fresh floor marks. The main culprits should swiftly emerge after a few days and then customer services can deal with these individually.
Rancid-smelling yellow/ brown marks: If the marks occur on chefs' wear, then a specific, well-designed process will usually remove the marks completely. Problems arise when the kitchen uses pillowcases and napkins for mopping up or catching cooking oils. A typical pillowcase process will not work and the marks will often survive even a process designed for table linen.
The problem becomes acute if the textiles contain polyester because this is oleophilic, meaning that it attracts and holds the oils very strongly (as users of cotton-rich bed linen have found).
Table linen processes with a shrewdly chosen emulsifier can handle this, but if cooking oil marks remain on a polyester or polyester blend pillowcase, then they will oxidise and set onto the polyester yarns, creating rancid smells and yellow brown patches that require a severe re-wash.
Re-wash process design
There is no point in putting linen with residual stains back through the same, standard wash process.
A good, general purpose re-wash process consists of a high temperature, main wash process that is dosed with plenty of detergent, (typically 15g/kg of textiles) and plenty of alkali (typically 20g of a standard alkali booster per kg of textiles). There is little point in a pre-wash stage for such a wash.
If rancid odours and yellow brown marks from oxidised oils are a problem, then use a high-temperature wash with an appropriate emulsifier. This will probably need only a very little detergent, as foaming should be avoided. The key here is to match the emulsifier's HLB (hydrophilic-lipophilic balance) value to that of the oils and greases to be removed.
Spa oils pose a particular problem but the correct emulsifier should solve this and the detergent supplier should be able to advise on the choice.
Getting the re-wash right for residual cooking oils and for spa oils has the additional benefit of considerably reducing the laundry's fire risk as these oils can be a prime cause of spontaneous combustion. There have been recent fires from this cause both in laundries and on customers' premises.
Developments in emulsifier chemistry have now produced additives that will not only take out spa oils, but can do so in a tunnel washer.
White linen that has been tinted by a stray coloured item such as a red linen or paper napkin can often be recovered successfully, even if sodium hypochlorite bleach has no effect. It is generally worth trying a process based on sodium dithionite (which is a reducing bleach rather than an oxidising one). Special safety considerations apply, so seek advice from your detergent supplier.
Finally, the laundry will need a dedicated re-wash process for metal marking from rust marks (and other metal oxides of manganese, copper, vanadium, nickel, chromium and so on).
Provided the metal oxalate is water soluble, then a 15-minute main wash at 60 - 80C (the hotter the better) with 20g oxalic acid crystals per kg textiles will take out otherwise irremovable metal marks, even those from knife cleaning.
This process will only work in a washer-extractor and even then there will be some attack on the metal of the washer, so it should be reserved specifically for metal-marked textiles and never form part of a general
re-wash system. Do not add detergent to this special metal-mark process as doing so will neutralise the acid, and stop it working.
Review your re-wash processes
Most types of normal but severe stains can be now be recovered with the right treatment. There is even some prospect of recovering abused linen and the black marks caused by corrosive failures in a tunnel washer.
A thorough review of the laundry's procedures for recovery washes should bring substantial benefits.