Guest Post: How to Measure Quality and Use This to Rate Detergents

| Feb 18, 2021 3:00:00 PM

Wash quality is a key factor in decision making for detergent purchase and even for washing machine selection, and now this can be reliably measured (numerically) using simple and readily available pre-stained test fabrics.

It is also possible to measure long-term greying after multiple laundering and minimise this in a variety of simple ways. Perhaps the most valuable quality measurement is that related to removal of different types of oily soiling and staining, because some types of oils have been linked to laundry fires which are believed to have been triggered by poor washing performance.

Spontaneous combustion is thought by many to be responsible for several laundry fires and their stocks of textiles, at significant cost. This month we also look at how you can minimise this serious risk.

Measuring whiteness retention and long-term greying

Greying in washing:

White and pastel-coloured textiles can become progressively greyed after multiple laundering, because of poor classification, the wrong detergent system in the wash, or over-drying. Greying in washing is predominantly caused by re-deposition of soiling in the wash liquor back onto the clean textiles, usually in the main wash. A good detergent formulation is designed to counter re-deposition by incorporating a suspending agent, which wraps around each bit of loose soiling to neutralise the tiny electro-chemical charge, which would otherwise attract it back onto the clean fabric and saponification and/or emulsification of fats and oils.

Pastel – coloured textiles can also change colour – appearing to grey if washed using a detergent containing OBA (optical brightening agent)

Detergent dosage:

Sometimes correcting greying needs nothing more than an adjustment to the detergent dosage, to ensure an ad equate amount of suspending agent is added every time. A premium detergent, containing a good concentration of suspending agent, is designed to prevent greying without requiring an excessive dosage.

Hard water:

Can lead to greying due to the production of scum and the hardness impurities reducing the effectiveness of the detergent.

Iron contamination (Fe++):

Can lead to an overall brown shading to linen as well as localised rust-coloured spots.

Turbidity:

A measure of the degree to which the water loses its transparency due to the presence of suspended particulates may also be a contributing factor, especially from well water.

Classification:

Textiles carrying heavy soiling should be separated from lightly soiled work and the detergent dosage adjusted appropriately.

Dye transfer:

This can be an issue if water is recycled or if white and coloured items are washed together.

Greying in drying:

If textiles continue to be tumbled when they are bone dry, the friction as they rub against the walls of the rotating cage and against each other creates a tiny electric charge. This acts as a ‘magnet’ for every dust particle in the drying air stream which causes long-term greying. This increases with every wash and it gets worse with every few seconds of the over-drying to which the textile is subjected. The optimum endpoint for drying towelling is that which leaves about 2% moisture in the finished towels, which is sufficient to prevent the charge from building. This produces towels which not only stay whiter but are also softer to the touch and can often delight the guest user.

Greying is measured using a Laundry Reflectometer:

Large laundries often have their own; others use the one carried by their detergent supplier. The modern meter delivers a percentage score running from 0% (a black hole) right up to 100% (pure brilliant white light). Some contract customers, especially in healthcare, specify a minimum whiteness for their clean textiles (typically 92% – 94%), in order to build this aspect of quality into their expectation from the laundry service. There is sound logic in this, especially for healthcare, because much healthcare soiling is protein based. If this were to build-up on the textile surface, it could provide nutrient to encourage microbial growth in, say, care-home linen storage cupboards.

Measuring stain removal performance

Calibrated swatches of specific test fabrics are available from LTC Worldwide, to enable accurate comparison of different wash processes with respect to each of the following types of soiling and staining:

Protein stains:

Stained shirts and clean shirts_HydrofinityFluids from an animal body (including the human body) are generally protein based. They include, blood, urine, faeces, mucus and many fats, oils and greases. Gravy, beef dripping, milk and cheese are just a few of the animal-based products which give rise to protein stains. One popular test swatch for protein removal is based on a mixture of blood, milk and carbon black. This swatch is stitched to a carrier cloth and washed once in the target process. Its colour is then measured using the same Laundry Reflectometer as was used to assess greying, on the same percentage scale. It has been found that a process which scores above 40% by this method is usually adequate for most hospitality work, although food industry customers do sometimes require 45% or even 50%.

Vegetable dye stains:

Substances from plant life (anything which originally grew in the ground) usually contain dyes which discolour the textile. Strong examples include beetroot, blackcurrant and tomato. Fainter, but no less irritating, stains can be caused by beer, orange juice and champagne. Vegetable dye stains often cannot be washed out of the fabric, they have to be de-coloured by chemical oxidation. Launderers used to rely on sodium hypochlorite (‘chlorine bleach’), but this reduces the life of cotton goods and can produce indelible yellow-brown stains on healthcare work (and even occasionally on hotel and spa items). A safer alternative for these goods is hydrogen peroxide. The latest detergent systems tend to use peracetic acid (which involves acidified hydrogen peroxide, increasing its power).

The effectiveness of removal of vegetable dye stains can be measured accurately and numerically, on a percentage scale, using a calibrated test swatch stained with iridium dye. This is washed once in the target process and the colour is then assessed using a Laundry Reflectometer. For most hospitality work, a typical score of 40 - 50% has been found to give adequate stain removal performance to meet customer requirements.

Oily stains:

These fall into three groups. Proteinic fats, oils and greases should be dealt with as protein stains (see earlier paragraph). Vegetable oils occur in nuts and other seeds and fruits and include, for example, olive oil, pumpkin oil and nut products generally. One popular test swatch for vegetable oil marking is stained with olive oil and carbon black, and a reflectometer score of 40-50% after one wash has been found to meet most customer requirements. Mineral oils, fats and greases occur in petroleum products used in automobiles, industrial machinery, lubrication of domestic appliances and in some healthcare applications. These can be assessed using a popular test swatch based on lubricating oil and carbon black. The required test score after one wash should be agreed separately with the customer, as requirements vary considerably.

Special stains:

Spa oils, certain products used in the motor trade and oils used for decontamination of metal parts in industry require special, expert treatment. There have been instances of spontaneous combustion of textiles on the launderer’s premises, often overnight when there is no one present. This has led to extensive damage. The risk is minimised by processing soiled items on the day they are received and by ensuring that the wash process removes the soiling with a process designed to achieve this. Cooling the goods before folding and packing out is also a sensible precaution, but the essential key is to get the wash process right.

There are, to the best of our knowledge, no commercially available test swatches to assist with this, but leading detergent suppliers are able to advise on the correct wash product and dosage to achieve safe removal. The secret usually lies in the choice of emulsifier and the ability to match this to the specific products to be removed. With spa towels, there is often a characteristic odour from the products used in the spa treatment. The launderer should aim, as an absolute minimum, to remove this odour completely and might then use a simple ‘sniff-test’ on every batch for very basic quality control.

Assessing the detergent

The function of the detergent includes removing the soiling and staining and preventing long term greying. The test swatches are designed to enable the launderer to rate each of these functions accurately and numerically, permitting justified comparison between two competing products. This may involve washing the test swatch from one to twenty-five processes. It is important when carrying out this exercise to use the dosage recommended by the detergent supplier and to include costings in the comparison, because doubling the dosage of an inferior product could produce an acceptable result but at considerable cost.

Effect of machine choice

Most washer extractors are much of a muchness, with perhaps one exception. That is the Hydrofinity machine, which displaces much of the water for the process with XOrbsTM.

This produces at least two impressive results: firstly, it means that the water required for the main wash is roughly halved, so it uses only half of the detergent dose that would be required to make the necessary concentration in the wash liquor.

Secondly, the XOrbs are designed to attract oily staining. The combination of these two factors might be why some users have reported such excellent performance from this machine when delivering a shirt service, with low temperature washing removing even stubborn collar and cuff grime. This is usually protein-based soiling from skin sebum from the neck and wrist, which can be difficult to remove at low temperature.

Conclusion

Quality can be measured accurately, and the results used to control washing performance and to do this at an affordable cost. In the present commercial climate, this is becoming essential and the tools are readily available.

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