Managing rewash

This month we look at how switched on launderers manage rewash effectively and how every laundry can match their superior performance. The secret lies in using modern laundry technology to exploit low-temperature stain removal whilst reducing residual staining, so that large quantities of circulating stock do not need washing twice. This removes double handling and in the case of towelling, wasted tumbler minutes. Here is how to set about it.

Stain removal

The secrets of effective stain removal are not universally applied, and the result is very varied performance from different laundries. There are three groups of stains on most classifications:

Vegetable dye stains from tea, coffee, beetroot, red wine and anything which came from plant life, require chemical oxidation to de-colour them. Unfortunately, oxidising agents also degrade cotton, causing premature tears and excess lint on the dryer filters in the case of towelling. This means the dosage must be carefully controlled; if this is done correctly, then it is quite possible to obtain over 200 wash and use cycles from the circulating stock and still get total removal of even the worst red wine or beetroot spillages.

Protein stains from meat juices, dairy products, blood and anything which came from the human or animal body, require softening in the pre-wash. Many will then come away with normal mechanical action and detergency in the main wash, provided this is carried out at the temperature specified by the chemicals’ supplier. There should be no need to overdose with bleaches to get protein stains out. This simply causes accelerated rotting of the cotton fibres and reduces textile life.

Oily, fatty stains come from some proteins (blood, and fish oils, for example). They also occur in many plants (essential oils from spa treatments, such as eucalyptus oil, for example) and they make up a variety of mineral oils. The hard way to remove these is with high detergent dosages in high-temperature main wash, which runs for a long time. A much better way is to soften and solubilise them with an emulsifier, starting in the pre-wash. They will then come away with normal detergent dosages and open the way for low-temperature washing.

Just using any old emulsifier will not work on every fatty, oily stain. To achieve very low rewash, the HLB (hydrophilic lipophilic balance) ratio of the emulsifier must be matched to that of the staining. If you are washing towels and sheets from a spa, for example, you will need an emulsifier with a very low HLB value (probably around 7). If you take the trouble to get this right you will find massive improvements in product quality for spa textiles (no rancid odours) and textile life (the rancid fats tend to be acidic and rot cotton). If you have to deal with every type of oily stain you may need a wide-range emulsifier, which are a little more expensive but usually well worth it.

Low temperature washing

Energy is expensive and the steps now being taken to avert climate change are unlikely to make it significantly cheaper. Laundering uses about nine times more heat energy than electric power, so it makes sound sense to minimise this first. Most launderers have reduced heat energy demand in washer extractors from around 1kWh/kg dry textiles down to 0.6kWh/ kg (by optimising wash dips and tightening temperature controls). The next step has been to introduce low temperature washing and one of the keys to this has been sorting out stain removal. Getting this right has enabled low energy washing, particularly using the latest emulsifier technology to remove protein staining, as described in the previous paragraph.

Energy recycling

Utilisation of waste heat streams from the laundry has been widely promoted and increasingly taken up. Using the waste heat in the ironer exhaust and in the central boiler flue has enabled generation of warm water for the washhouse, but this is much less valuable now, with the advent of reduced temperatures in the main wash in washer extractors and in the washing zone of a CBTW. In any event, producing a warm water supply for a CBTW can be counter-productive, because the fresh water supply to this machine is used in the rinse, which is then recycled internally to the front of the machine for the pre-wash. In many cases this results in the pre-wash temperature going above 40C, the critical temperature for setting of protein stains. Several users have found their stain removal performance declining sharply when this has happened, especially on hospitality linen and food industry workwear.

It therefore makes sense to focus investment in recycling on tumble drying (where a controlled portion of the unsaturated exhaust airstream can be returned to the air inlet) or on minimisation of water use in a washer extractor-based washhouse (by utilising the final rinse to satisfy pre-wash and main-wash water requirement). Low temperature washing is eliminating the demand for hot wash water and the central boiler house is unlikely to survive the transition to gas powered finishing equipment.

Mechanical action

Efficient removal of protein stains still demands good mechanical action in the main wash. This means eliminating overloading and under-loading, neither of which give an adequate ‘lift and drop’, or item to item abrasion, to lift the softened protein stain out of the fabric. Optimum stain removal for multiple clients is generally achieved by sorting by classification, rather than by trying to keep all articles belonging to one customer together. The best arrangement is that given by a pooled rental stock, with each batch of similar items being correctly weighed into the washer.

Greying and tinting

Greying and tinting are both forms of overall staining which are caused by the launderer, rather than simple stains that are put on by the user.

Greying is caused by re-deposition of soiling which has been washed off the textiles and which then succumbs to the electrochemical attraction (which all textiles display) towards loose soiling floating around in the wash liquor. A good quality detergent system is formulated with enough suspending agent in it to wrap around each bit of loose soiling and neutralise the attractive charge. A good suspending agent will also form a physical barrier between the soiling and the textile, to further hinder any tendency to re-deposition (and hence greying). Leading detergent suppliers generally take responsibility for greying in washing caused by re-deposition, because avoiding this is part of their craft skill. (However, they are not able to prevent greying in tumble drying caused by failure to terminate the cycle at the correct point. Over-drying is a common cause of greying, even in the best run plants.) There is no quick way of reversing greying, caused either by re-deposition or by over-drying. It will take many washes with a properly designed process and good dryer control to reduce it.

Tinting is caused by poor classification, when white textiles are mixed in with the occasional coloured item, often accidentally. However colourfast a supplier believes his textiles to be, it is folly to risk mixing them with white items. Recovery of tinted items is often possible, although they can rarely be rectified with an oxidising bleach (such as sodium hypochlorite or hydrogen peroxide). They often react favourably to a reducing bleach, such as sodium dithionite (formerly called sodium hydrosulphite). Caution is needed, both in storage and in use with this chemical, and the advice of the supplier should be sought and followed to avoid safety issues.

Textile life

It is an old-fashioned fallacy that improving stain removal requires an acceptance of reduced textile life, because this was based on the assumption that perfect stain removal required excessive bleaching with sodium hypochlorite (and therefore rapid rotting of the stock). Modern stain removal is possible without degrading the stock and if done correctly at low temperature, it is reasonable to expect improved life.

Designing the rewash process

A great many launderers still treat rewash by putting it back into the same process as failed to get it stain-free the first time. Leading operators now have dedicated rewash processes with superior protein removal power (usually higher alkalinity and/or stronger emulsification) and sometimes stronger oxidation. Work from these processes is sorted into stains needing special treatment (for iron, mildew or aluminium markings) and scrap.

Iron marking is taken out using a dedicated process consisting of one hot wash with oxalic acid crystals (the design of which your chemicals supplier should be able to assist with) followed by three good rinses. The iron oxide marking on the textiles is converted to iron oxalate, which is soluble and goes to drain at the end of the wash).

Aluminium marking is taken put with a dedicated process which starts with a hot, high-alkali wash (to solubilise the aluminium as its hydroxide), again followed by three good rinses.

Marks which look like rust but do not come out with the iron removal process may well be from chlorhexidine disinfectant, which is a common constituent of modern skin treatments (it occurs in Savlon fo example). Chlorhexidine stains go into the normal wash colourless, but if the process uses sodium hypochlorite, a chemical reaction occurs which produces an indelible (and irremovable) stain which looks just like a rust mark

Conclusion

Successful laundering requires many skills and adoption of the latest in laundry chemistry and careful implementation of this has enabled great improvements in stain removal without necessitating significant cost increases. In fact, low temperature washing and greater water efficiency have lowered costs. Unsurprisingly, this is starting to raise customer expectations and critical clients have increased their complaints when these expectations are not met.

If you have problem that you think LTC Worldwide can help with, or that you feel would make a good subject for Material Solutions, please call T: 00 44 (0) 816545 www.ltcworldwide.com