The basis of almost all cleaning products is one of two things, either solvent or water. These have several functions but, fundamentally, they are the carrier for whatever contamination one desires to remove. Of course, not all contamination is readily removed so additional components are added to help optimize the cleaning.
The most common additives are surfactants. Surfactants added to water based systems, for example, will assist in making the system compatible with oily contamination. As a result, the water will be more efficient at wetting the contamination and thus more efficient at removing it. There are many other additives possible which act in a similar way. Acidic additives will help in converting insoluble elements into forms which can be solubilised by the system. Alkaline elements will often work analogously to surfactants thanks to the saponification of oils to form soaps (which are basic surfactants in their own right). Sequestrants act in some ways like the acidic elements – they can help dissolve soiling which is otherwise insoluble in the system. They are often combined with alkalinity boosters since their efficiency is optimal at specific pH values.
Whilst there are many thousands of potential additives, they are almost always present to facilitate the natural action of the solvent or water which is the element ultimately responsible for the cleaning.
Acid based Cleaning
Acid cleaners are generally used when metals or metal salts need to be removed. Often these are highly insoluble in water based systems. The acid reacts with the soiling/contamination, converting it into a water soluble form. An example of this is rust removal. Whilst the most obvious parameter in acid cleaning is the ‘strength’ of the acid and thus the pH, the chemistry of the counter ions is also important. For instance, the use of hydrochloric acid for stainless steel cleaning will result in permanent damage to the surface whilst nitric acid is quite safe. As a result it is important to use the correct acid.
Alkaline based Cleaning
Alkaline cleaners are the most common product type, primarily because most soil types are acidic in nature. They are also used because of the detergency produced as a result of the reaction with oily components. They can be broadly separated into two groups – caustic and non-caustic. Caustics are sodium/potassium/etc. hydroxides and are extremely potent and dangerous. They produce solutions which are extremely high in pH and they are highly corrosive to many materials, even at low concentrations. Non-caustics can be any range of alternative chemicals but these are typically much safer and much less corrosive. Whilst caustic products do present a notable risk to both the surfaces being cleaned and the user, on an equivalent cost basis, they will be more effective than non-caustics – as a result they are very common. In high end cleaning it is very important to be aware of all the materials the product may contact before the use of caustic products since they can cause irreparable damage to sensitive surfaces (such as trims) and can even be responsible for ‘frosting’ of glass. As a result, unless the user is experienced and well informed of the hazards and/or the cost is the primary consideration, non-caustic products should be preferentially used.
pH Neutral Cleaning
The use of pH neutral products is typically in response to surface sensitivity. Typically the corrosion resulting from these products will be notably lower than acid/alkaline products. Unfortunately the trade-off is that they are either less effective or require advanced additives which result in increased cost. In some cases this is warranted and in others not.
Solvent based cleaning
Here the water is replaced by an alternative solvent. Most commonly a solvent based cleaner is used when the level of soiling is high and is of a character incompatible with water based systems. Oily soils can, as explained earlier, be removed by surfactants (a relatively gentle process, but with limited effectiveness with heavy hydrocarbon soiling) and alkalinity (can require strong caustics which, whilst effective, can be far too aggressive to the underlying materials) but the correct choice of solvent can often result in a product which is much more effective, much less hazardous and much safer for the area being cleaned.
An additional note in this area is with regards to pH. pH is a measure of the concentration of hydrogen ions in an aqueous solution. The term aqueous is critical here – if a product is based on a solvent then it does not have a pH. It is increasingly common on internet forums that individuals and even companies will discuss the pH of solvent based products. There are even instances where pH meters will be used to measure this. Unfortunately this is entirely meaningless and the practice will give results which do not reflect the concentration of hydrogen ions or the acidity/alkalinity (which are not specific to water based systems) of the product.