Finding answers to towel laundering problems

12 August 2014



Richard Neale of the Laundry Technology Centre suggests ways to approach towel laundering that will produce a good result while avoiding risks and maintaining a cost-effective operation


The laundry and textile rental industry is in the business of cleaning textiles and ensuring that whites come out of the process looking bright.
While still aiming to produce a good standard of result, the industry must find ways to counter intense cost pressures that are made even greater by the ever-rising costs of energy in all its forms. Many laundries are setting tough target reductions of up to
7% year-on-year and are steadily achieving these
For laundries offering a towel service, especially for both spa and hotel use the difficulties involved in reducing costs may be affecting the laundry's ability to produce towels that are white, stain-free and smell fresh, leading to disappointed customers.
Fire risks may also get overlooked, and as a result insurance costs for the sector are being pushed up to very high levels. The answer is to address customer concerns, fire-risk, quality and operating costs together.

Getting towels clean and fresh
Modern detergent systems are designed to do a very good job at stain and soil removal when used at very low concentrations in the wash liquor.
This does not mean reducing the dosage below the level needed to get the work clean and even more importantly the dose must not drop below a level that will prevent greying in the wash.
The most important ingredient in the detergent (as far as greying is concerned) is probably the suspending agent. This is designed to wrap the removed protein soiling and to hold it in suspension so that it all goes to drain at the end of the wash stage.
Reducing the dosage below the critical level allows soiling to re-deposit onto the cloth, producing greying, which gets worse with every wash. This is partly the reason why two- and three-year old towels often look grey and dingy when stacked with their brand new counterparts.
Reducing the amount of wash liquor to a low but safe level is an essential first step to reducing the detergent dose.
For the washer-extractor this usually means a running dip of around 7.5cm, which should be set accurately using a well-damped dip tube.
Safely minimising the wash liquor level in a tunnel washer means setting the wash-water flow to the safe minimum and keeping it there.
The variable area flow-meter needs at at least a weekly clean and calibration check to ensure that this is done accurately.
The risk of tunnel blockage can be minimised by setting the weirs so that there is no danger of the main-wash compartments running short of water. The detergent supplier should be able to advise in detail on the procedures.

Essential oils on spa towels
All launderers have difficulties in removing treatment oils from spa towels. Even the best launderers are reporting that these towels still have aromatic odours when they are unloaded
from the dryers.
In cases where removal is very poor, launderers are inundated with complaints about foul, rancid odours.
This is because spa treatments frequently involve highly refined essential oils, which smell sweet but which do not succumb to normal detergency.
The usual solution to removing these oils, and therefore any lingering smells, is to use an emulsifier but this alone does not solve the problem completely. Firstly, the spa towels need a higher level of detergency (sometimes double or even treble the normal dosage, especially if the laundry is trying to re-cover rancid towels).
Secondly, the emulsifier properties must be matched to the oils to be removed. The important factor here is the emulsifier's HLB (hydrophilic lipophilic balance)'.
Most emulsifiers used in the industry are designed to deal with essential oils with a broad range of HLB value but if the oil has an HLB value outside this range, the process will not work. As a result, the towels will darken and degrade in the tumble dryer, progressively developing foul and rancid odours.
The leading detergent suppliers are adept at dealing with this kind of problem, although they will need to know the ingredients of the "difficult" spa treatment. It may be that a different emulsifier is needed or perhaps a blend of emulsifiers.
The laundry needs to solve the problem, not only to satisfy one or two difficult customers, but also because if towels are being supplied from pool stock, the whole stock will eventually become contaminated. Many customers and rental operators use coloured towels for spas and pools for this reason but they must still be clean and odour-free.

Fire risk
Towels stained with essential oils pose a significant fire risk and this is yet another reason why it is essential to remove these oils, however difficult it may prove.
Laundry fires generally occur as the result of spontaneous combustion when soiling that has not been removed in washing starts to oxidise in drying. Unless the towels are cooled very thoroughly, then there is a considerable risk of oxidisation continuing in the centre of the pile of warm towels in the despatch area.
If the heat generated (this is an exothermic reaction) dissipates, without heating up the pile, this will not cause a fire but if the centre is insulated by the towels around it then the temperature rises exponentially and fire breaks out spontaneously and explosively, throwing a pile of flaming towels in all directions.
It is therefore important to get this stain removal on spa towels right and avoid the risk.
If the towels can be washed in a washer-extractor then the detergent dosages can be adjusted and the solution found. This can be confirmed every time the towels are washed just by sniffing the warm towels from the dryer.
In a tunnel washer, the detergent and emulsifier immediately start to travel forward with the work (which is good) and backwards with the water flow (which can divert them from the soiled areas),. In this respect, a tunnel washer with a co-current standing bath arrangement for the main wash will give a better result more economically.
For the general tunnel washer, with counter current flow through the wash zone, it is best to separate the spa towels into short runs to process as many batches as possible in one run, without blocking the dryers and creating tumbler "holds".
So for example if there are six tumblers, a batch of five spa towels might be possible, with batches of
work to be ironed to precede this and to follow it.
The work for ironing can go through the sixth dryer within the cycle time, avoiding delays.

Greying in the tumble dryer
Overdrying in the tumble dryer is the most common cause of two- and three-year old towels becoming grey.
The optimum moisture content of a finished towel is 4 to 6%, calculated on bone-dry weight, not air-dry weight. Towels dried beyond this level will pick-up moisture from the air in the laundry or in the hotel guest's room, so overdrying wastes both money and tumbler time.
Drying below 4% moisture will also affect quality. Once the tips of the terry loops are bone dry, they do not have any moisture that would dissipate the static charge that is generated when the textile brushes against the dryer's metal cage.
As a result, the towel surface attracts every particle from the drying airstream leading to progressive greying. This is the main cause of grey and dingy towels, rather than greying in the wash.
The degree of greying in the dryer can be measured by taking two new towels, folding one into a small net bag and stitching the other to the outside of the bag so that it can float freely.
This combined test piece is washed and dried 25 times and then the towels are finally dried and compared. Both towels have been washed 25 times, but the one folded into the net bag will not dry properly. The difference in colour between the two towels (measured by whiteness reflectance value) indicates the degree of greying in drying.
The difference in colour between the towel washed in the bag and a third brand new towel indicates the degree of greying in the wash.
The best way of minimising greying in drying is to fit the tumble dryers with automatic cycle terminators set very precisely to give a minimum 4% moisture in the dried towel. The end-point setting must be exact.

Avoiding hardness and harshness
If the laundry is under pressure there is a great temptation to minimise drying times by setting the gas burners to give maximum inlet temperature (so as just to avoid scorching).
Doing this will mean that the towels start to dry before the terry loops float free from the surface and the result is a much harder flatter towel.
The ideal is to start the drying at a lower temperature so that the cool towel has time to break up and regain its full thickness before drying really gets under way.
When this staged process is combined with control of the final moisture content, it will be found that the towels will be close to their "as-new" thickness and will be soft, with no trace of either hardness or harshness.
The customers will be impressed and delighted with the difference. They will be even more impressed in the second and third years, when the older towels look as white as the new ones.
This is also a good time for the laundry to review the need for high levels of towel bleaching and to strive to get a fourth year from the towel stock, now that it is still soft and fluffy and white.
The suggestions here are not exhaustive, but they are intended to offer a way to counter the high charges imposed by insurers and to address the continuing need to achieve progressive savings. Combined with savings in energy and improvements in quality, this approach will help to answer some of the main problems that launderers can face.



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