A manufacturer made small, aluminum tubular parts, about one inch in diameter, for one of its customers. The parts were used in highly sophisticated equipment. One of the problems the manufacturer was encountering was removing chemical residue left on the parts during the manufacturing process. Not only did the residue have to be removed before the parts could be shipped, there were concerns that acids might be entrapped in the parts, which also had to be removed.

The company turned to a leading product finishing expert for advice. The expert suggested, “I would first recommend rinsing [the aluminum tubular parts] thoroughly in a cold water rinse. Then go back and forth between a hot rinse and a cold rinse. This will cause expansion and contraction of the ‘pores,’ or surfaces, and will most likely rinse out all of the residue.”¹

While cleanroom environments may not be manufacturing tubular parts, they may be dealing with chemical residue in more ways than they realize. And one of those ways may actually be in the way the facility is cleaned. The challenge is that chemical cleaning solutions invariably leave some residue on the surfaces on which they are used and this residue can become such a problem, it has the potential of taking “clean” out of the cleanroom environment.

Learning from carpet cleaning

When wall-to-wall carpet became popular after World War II, about the only way to clean them was by using a shampoo or bonnet cleaning system. While the two systems differ, for our purposes in this article those differences are of no consequence.

Both systems involve applying a chemical cleaning solution to the carpet to help dissolve soils. From here, a rotary floor machine is used on the carpet to provide the necessary agitation to loosen and remove those soils. So far, so good. In most cases, the carpet looks very good right after cleaning and some chemical manufacturers add ingredients to “lighten” and “brighten” the carpet, enhancing its just-cleaned appearance.

However, things invariably start “going south” within two or three weeks after cleaning. This cleaning process leaves considerable amounts of chemical ingredients in the carpet. While vacuuming helps remove some of this chemical, what remains could be compared to a magnet. As building users walk over the recently cleaned carpet, soils, dust, and contaminants on shoe bottoms are all drawn to the carpet, causing what is known in the carpet cleaning industry as “rapid resoiling.”

In essence, the carpet returns to the drab and soiled appearance it had before cleaning. The same can happen on other surfaces, including many of those in a cleanroom setting.

“Immediately after use in surface cleaning, detergent molecules remain chemically unchanged [on the surfaces],” says Dr. Jay Glasel, managing member and founder of Global Scientific Consulting LLC. “A small but finite amount of detergent remains — in all too many cases — as residue on the surface.”²

Soiling is just one problem related to chemical residue left on surfaces. Chemical residues can also become airborne and be inhaled, potentially causing asthmatic and allergic reactions. Some facilities are so concerned about chemical residue left on surfaces that they contact organizations and laboratories specifically to test, analyze, and detect if any chemical residue is on a surface. Chemical residue can not only cause rapid re-soiling or have negative health impacts … it can also result in discoloration, stains, and corrosion of some surfaces.

Cleaning without chemicals

So it appears the only way around this situation, especially in a cleanroom environment where the cleanliness of surfaces is paramount, is to find ways to clean without chemicals. But, before we jump that far, there are some non-traditional chemical options.

For instance, more and more chemical manufacturers are introducing bio-enzymatic cleaning solutions. They are doing this because these cleaning solutions, which contain enzymes that essentially digest soils, have a reduced impact on the environment. But with bio-enzymatic products, “cleaning professionals don’t have to worry as much about leaving chemical residue behind,” says Laura Craven, director of communications and marketing for Miami-based Dade Paper. “With bio-enzymatic products, the residue continues to consume organic material and helps control odor.”³

However, even with bio-enzymatic cleaning solutions, some residue remains. And issues arise as to proper application of the solution, and where and how it has been applied. For instance, bio-enzymatic products are often used to kill odors. Many times they are just sprayed on to a surface or hard-to-reach area which may be the source of the odors. If not wiped away, cleaning solution is left to dry on the surface, leaving more chemical residue.

True no-chemical options

While bio-enzymatic products can help, they do not end the chemical residue problem. There are two options that cleanroom managers can consider. The first is what is called vapor cleaning, which has a long history in the professional cleaning industry.

A vapor cleaner generates pressurized steam via an internal boiler. Used for professional and not consumer use, vapor cleaners heat water to 250 F or more, hot enough to destroy most germs, mold, mildew, bacteria, and other contaminants, leaving surfaces clean. Once cleaning is over, moisture evaporates and no chemical residue is left on surfaces. The key issue with vapor cleaning is that, while effective, it is a slow process and because cleaning is very labor intensive. This means it can also be a costly process.

Another option is the use of aqueous ozone cleaning systems. Ozone, as we know, is naturally found in the atmosphere. However, using water and oxygen, it can be engineered into aqueous ozone and then infused into water. Dispensed through a wall-mounted “fill station,” as it is often referred to, or from a portable rolling “caddy,” it can now be used for many cleaning tasks, on-site and on-demand which helps improve worker productivity.

“While aqueous ozone technology is relatively new to the professional cleaning industry, it is certainly not new in other industries,” says Matt Montag, National Sales Manager for CleanCore, manufacturer of aqueous ozone cleaning systems. In the U.S., aqueous ozone has been recognized safe as an antimicrobial agent for the treatment, storage, and pro-
cessing of food products since 2001.

These systems have also been tested as to their effectiveness. In September 2015, the University of Nebraska Medical Center released two studies regarding the use of aqueous ozone for cleaning. According to Montag, they found that these systems proved very effective at reducing colony-forming units (CFUs) of both E. coli and listeria from hard sur-
faces, comparable in many cases to the key ingredient found in sanitizers and much more powerful cleaning solutions.

Explore your options

It was easy for floor covering manufacturers to realize they had a problem. To eliminate chemical residue, extractors that vacuum up chemicals and other systems were developed, including new chemicals designed to eliminate chemical residue in carpet.

However, for other surfaces, the problems caused by chemical residue are less visible — until they cause a problem, as with the tubular parts discussed earlier. Cleanroom managers should be aware of the potential negative impact of chemical residue on surfaces and, to be safe, consider the no-chemical options mentioned above that leave no residue whatsoever.

References

1. Chesterfield, L. “Rinsing parts with entrapped chemical residue,” Products Finishing Magazine, Nov. 1, 2005.
2. Cooper, S. “The Hidden Hazards of Cleaning Residues,” Cleaning Maintenance Magazine, Jan. 3, 2013.
3. Garrett, R. “Enzymes and Bacteria Add a Powerful Punch to Cleaners,” Contracting Profits Magazine, Nov. 11, 2014.

Robert Kravitz of AlturaSolutions Communications is a frequent writer for the professional cleaning and building industries. [email protected]

This article appeared in the July/August 2016 issue of Controlled Environments.