Much has happened in the last twenty years to revolutionise laundry chemistry – not all of it good. Alongside the major advances in wash performance, there have been restrictions on laundry effluent which have led to the banning or much reduced use of some very effective ingredients. This month we review the results of some of these changes and point the way forward for getting the best ‘bang for your buck’ from the detergent recipes which are still available.
As late as the 1960s, much washing was still done using pure soap (sodium stearate) and alkali (usually sodium carbonate or sodium metasilicate). This worked fairly well, provided the water was softened down to zero degrees of hardness. Even then, there was still much grey scum formed in hard water areas by the formation of ‘lime soap’ (calcium and magnesium silicates). This happened despite softening of the laundry water, because hotels in these areas rarely softened water to the guest bathrooms, so used towels coming in with average moisture content of over 20% would rapidly exhibit progressive greying.
Pure soap gave way to synthetic detergents, produced inexpensively from petrochemicals, which removed most of the problem with lime soap scum, although the problem with hard water in towels from hotels in hard water areas persists to this day. It is one major reason why towels are so much more difficult to keep white than sheets and pillowcases (the other major reason being persistent over-drying of towel batches in the absence of accurate end-point detection in the tumble dryer).
The best detergents now contain sequestering agents to capture water hardness ions (from calcium and magnesium) and neutralise the greying and hard deposits which these would otherwise cause. Modern premium detergents also have a wider variety of suspending agents to prevent greying caused by re-deposition.
Objectives for the wash chemicals
General soil and stain removal is achieved fairly easily with the synthetic detergent component, providing the detergent dose is sufficient to enable emulsification of the oily and fatty soiling. The sequestering agent in premium detergents deals with the hardness ions on incoming soiled towels, so provided the main laundry water supply is softened right down to zero degrees, there is no problem in producing clean, white textiles for the hotel guest room.
By using a washing medium which is a mixture of water and XOrbsTM , the Hydrofinity design achieves high chemical concentrations for rapid, effective soil removal with lower detergent dosages (around half of those used in conventional machines).
Soil suspension (to prevent greying) also relies on an adequate detergent dose, with the premium detergents generally having higher soil suspension power. These ‘capture’ the loose soiling and suspend this in the wash liquor until the bath is drained.
Protein soiling and staining relies on complete emulsification of food residues, especially gravy based on meat juices, vegetable oils, chicken fats and fish oils and similar foodstuffs. The secret of removing these is to use a pre-wash that runs for at least four minutes at below 40C (38C is ideal), in order to soften the proteins so that they come away easily and completely with the mechanical action, detergency and temperature in the main wash. If the pre-wash stage is not executed correctly (for example if it is too short or if the temperature exceeds 40C), then the protein stains become set firmly onto the textile and removal is difficult if not impossible). A great many launderers still fail this basic test, and their rewash analysis often reveals many set protein stains.
Interestingly, the Hydrofinity design actually permits accelerated removal of fatty and oily staining, by absorption into the XOrbs, which may be why it gives such superb results on shirt service collars, with very effective removal of the grime around the inner collar.
More stubborn protein soiling may require an emulsifying agent in the detergent mix. This is usually added at the pre-wash, where most of it clings to the textile, so that it acts both in the pre-wash and main wash. Emulsifiers work by accelerating the break-up of difficult proteins, such as fish oils or beef fats (especially important on polyester blends). However, this only works if the laundry purchases an emulsifier with a hydrophilic-lipophilic balance (HLB) range which is matched to that of the soiling. For foodstuffs an HLB value in the range 9 – 13 generally works well.
Vegetable dye stains cannot be removed completely by washing alone, especially if they are aged and have started to dye the cotton fibre. The residual marks must be de-coloured by chemical oxidation, using an oxidising bleach (such as hydrogen peroxide in the main wash or sodium hypochlorite in the first rinse). Provided the fatty and oily staining from proteins and suchlike have been correctly removed, then very little bleach is needed to remove the vegetable dyes and very little chemical damage occurs to the cotton in the textile. It is only if the bleach dosage is increased, to chemically ‘burn’ set protein stains off the fabric, that the textile is life is abruptly shortened. This would be indicated by multiple holes and tears starting to appear in the circulating stock.
Whiteness retention is of major importance in modern laundering because the colour perceived by the customer is rightly used as a determinant of how good the launderer is at basic washing. Greying, yellowing and tinting can each result from incorrect laundering procedures or poor laundry chemistry. Most discoloration can be reversed by the skilful use of the correct recovery chemicals. Greying is prevented by use of a detergent dose that contains sufficient suspending agent to prevent re-deposition of loose soiling. Yellowing from local water which is excessively alkaline can be prevented using a chemical ‘sour’ in the last rinse. Tinting of whites can often be reversed using a high temperature treatment with sodium dithionite.
Colour retention is important if the laundry is supplying high quality cotton table linen for example. The customer with a smart restaurant will want their pale green tablecloths to be the same shade of pale green, not a variety from very pale to full and bright. This can be achieved by fine control of just two of the laundry chemicals which might interfere with this aspiration. Firstly, coloured table linen containing natural fibres such as cotton must be washed in a colour detergent which is free of optical brighteners. These ingredients of a normal whitework detergent are designed to bond to the surface of any natural fibre. From there they react with the ultraviolet portion of natural daylight (which is invisible to the human eye), turning this into brilliant white light. This has the effect of diluting the original colour of cotton or polycotton table linen, making it appear prematurely (and severely) very faded. Once the mistake is made it cannot be rectified, so care is needed to use a correctly formulated colour detergent every time
Secondly, care is needed in the use of bleach for the removal of vegetable dye stains from coloured cotton table linen. Some dyes fade with use of sodium hypochlorite, but they can often withstand hydrogen peroxide.
Rust removal may be required following removal of a bloodstain. Iron from the haemoglobin in the blood reacts with the oxygen in the air or water to form iron oxide (rust), which then dyes the cotton. Rust cannot be removed in any wash process. It needs special treatment in a washer extractor, using crystals of oxalic acid dosed into a high temperature bath at the rate of 20g/kg dry textiles. It is important not to add any detergent to this process as this negates its effect. Some laundries collect rust-marked work for regular weekly or monthly recovery in this way.
Aluminium marking is increasingly common, especially on cloths used in a modern kitchen, with many aluminium vessels and surfaces. These marks cannot be washed off, but they can be reduced in a single bath process using a single high temperature stage dosed with crystals of sodium hydroxide at the rate of 20g/kg dry textiles.
Washing machine design and laundry chemistry
Only one manufacturer (to our knowledge) has successfully built soil and stain removal into the actual design of their washing machine components. The XOrbs in the Hydrofinity machine target oily greasy soiling and staining and pull this off the fabric and into the XOrbs. This means that the Hydrofinity user can concentrate its detergency on other difficult aspects of the wash process, which may be why the manufacturers of this design claim such good soil and stain removal overall. To find out which laundry chemicals the Hydrofinity machine uses, read our specialist blog.
Modern detergent technology is a movable feast of ideas and novel compounds, which is constantly changing. This month we have concentrated on how the basic chemistry works and how to use some of the lesser known techniques to surprise and delight your customers. In a later blog we will be reviewing current trends and predicting where these will be taking us.