Acidic cleaning chemistries were discussed in a preceding blog. Now let’s talk about the second of the three classifications of chemistry we defined – caustics. Caustics are materials that are basic as opposed to acidic in nature. The use of caustics for cleaning, especially for removing oils and greases, can be traced to the ancients. Bases when mixed with oils form soaps! Soaps, in fact, are emulsifiers and are able to emulsify many soils. Our more recent forefathers made soap by reacting caustics (lye for example) with animal fats. Those of you who have had the occasion to encounter caustic chemicals know that when they are mixed with water and come in contact with your skin the skin becomes slippery. In actuality, the caustic has combined with the fats in your skin to produce soap – – but I’m sure you wouldn’t want to wash your face with lye every morning, or at all for that matter. Contact with concentrated caustics is, at best, not good for you! When it comes to removing oils and greases, however, the use of caustics is pretty much a “no brainer.”
In heavy-duty applications, caustics like sodium hydroxide and potassium hydroxide are diluted with water in concentrations that may exceed a 1 to 1 mix. Such concentrations, along with heat and mechanical energy are effective at removing oil, grease, and even oxides in some cases. High concentrations of caustic chemicals are generally safe to use on substrates which include steel, cast iron and stainless steel. Such strong concentrations, however, are not suitable for use on copper, brass and other relatively “soft” alloys. Aluminum, for example, is readily dissolved by concentrated caustics. The benefits of using caustics, however, is undeniable. This fact has led to the development of caustic chemistries that are compatible with almost any substrate.
One way to improve the compatibility of caustic chemistry with a wider variety of substrates is to reduce the concentration. Many “caustic” cleaners contain the actual caustic ingredients in concentrations far less than 10%. Another way to reduce the aggressive qualities of caustics is to use “inhibitors” as part of the formulation. Inhibitors, in essence, alter the characteristics of caustic ingredients rendering them chemically non-aggressive against specific substrates such as aluminum as well as brass and copper and their alloys.
Since caustic chemistries do not naturally possess the low surface tension properties required to make them effective at penetrating capillary spaces, most caustic cleaning formulations include wetting agents and other ingredients to improve their ability to penetrate. Most caustic cleaning chemistry also includes any of a long list of other ingredients to make them suitable for a specific use. These ingredients include emulsifiers, saponifiers, chelating agents (to “soften” water), and the list goes on. Most formulations are proprietary and are not disclosed other than an occasional mention of an ingredient that may be potentially toxic or otherwise environmentally unfriendly.
Although the formulation of caustic chemistries at first may seem relatively straight forward, it is really a very complex science and, in some ways, an “art.” Interactions between components and totally unexpected results (good or bad) are not uncommon.
Finally, a word of caution! If you find a chemistry that works in your application, stick with it! There will always be something out there that is “the same or better” than what you are presently using. Before making any move, first make sure that it produces the same result!
As you might imagine, this has been only a “brush over” of caustic cleaning chemistries. There are, it seems, whole libraries devoted to the subject. Future blogs will go into more detail on these and other chemistries.
– FJF –