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TECHNICAL MEMO #1: Choosing between powder and liquid alkaline cleaner formulations.

There are effective alkaline cleaner formulations in both powder and liquid form on the market that will handle most soil conditions, metal combinations, and washer configurations commonly encountered. Choosing between powder and liquid formulations requires consideration of some rather obvious factors, and others that are less obvious.

Safety and convenience in storing and handling the product are obvious factors, and largely a matter of personal preference. Spills of powder products are more easily contained, cleaned up and reclaimed than liquid, but it is generally easier to set up a liquid formulation for automatic control and replenishment, if this is desired (see Technical Memo #17: Automated Testing and Control). In storage, liquids are subject to damage from low temperatures, while powders can pack or cake in the drum, particularly after being opened.

Cleaning ability, if it varies between powder and liquid forms of alkaline cleaners, will usually favor the powder form. Special requirements placed on the cleaner, such as the amount of metal etch desired, soil-load tolerance, water conditioning requirements, rinseability, and pH favor the use of certain components. The low solubility of some of these highly desirable conponents makes it very difficult to formulate a liquid product that is both concentrated and stable. Solubility of the various components becomes a primary concern in formulating a liquid cleaner, with the result that some very beneficial raw materials may be left out.

The following table shows the solubility of some types of raw materials that are commonly used in alkaline cleaners. Many of the components listed serve more functions than the one that is shown. Solubility is cumulative, so once the solution is saturated, no more can be added. In general, the solubilities shown decrease dramatically as the temperature is reduced.

Powdered alkaline cleaners will generally have an overall cost advantage over liquid materials, even though the liquids are priced lower. Freight costs will be higher for liquid materials because a given operation will normally use three to four times as many pounds of liquid as they would powder. Container costs are also a significant factor favoring powdered cleaners.

Some will argue that the amount of surfactant that can be added to a powder product is limited by the need to produce a loose, dry product, while a liquid product can contain much more surfactant. This is partially true, but some surfactants are available in a powder form. There are also special physical forms of powdered raw materials that can be used to allow powdered cleaners to absorb and carry larger amounts of surfactant. Surfactants have limited solubility in water, and a hydrotrope, or "coupling agent" may be needed to keep them in solution in water. This adds cost, and may contribute to undesirable side effects, such as streaking.

I only raise the comparative difficulty of formulating a concentrated, stable liquid alkaline cleaner so that you will adequately question whether a liquid cleaner will do everything you want. Unless there is a good reason to choose a liquid material, I usually favor powdered alkaline cleaners because of cost considerations, and the relative ease of producing an adequate formulation.