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When it comes to pH and proper application to carpet and furniture cleaning, it can safely be said that many cleaning technicians are confused.
Different voices in our industry are stating conflicting points of view. Part of that confusion originates in that much of the training concerning pH is based upon generalities.
You might have appreciated the article by Dr. Aziz Ullah on the topic of pH in the August 2012 issue of Cleanfax magazine. It is important to understand that this is not the first time someone with higher-level qualifications, such as a Ph.D., has explained pH so specifically.
Here are some points you should review from Dr. Aziz.
- While the pH scale starts at 0 and goes to 14, it does not mean that there are no negative numbers or the scale cannot go over 14. In others words, there is a pH negative 1 and a pH 15. There is no need for there to be an emphasis on the scale in carpet cleaning training.
- While pH is about the ionization of water (H2O yielding H+ and OH-), that does not mean that other substances, such as alcohol, can’t have a pH as well. In other words, you do not always have to have water to have a pH.
The 0 to 14 pH scale was started in 1909 by chemist named Arrhenius. For the professional cleaner, Arrhenius’ scale is a well-designed theory of pseudo-science. A rough guess of its accuracy is 75 percent for the professional cleaner. There is a lot of junk-science that has come from Arrhenius’ theory because parts of it are not emphasized.
In 1923, two other chemists named Brønsted and Lowry developed a better theory. But is it really it necessary for us to know more about pH than we do now? We are kidding ourselves if we think making chemistry more complicated will solve our dilemma, but we do need definitive limits to avoid unwanted reactions from acids and alkalines.
Here are the three simple alternative approaches for the industry to consider:
1. The first is to use the pH number listed on the product container or from its material safety data sheet (MSDS).
2. The second is to use the pH reading, obtained with an electronic meter, directly from the freshly cleaned textile.
3. The third is to follow an accreditation program, such as the Seal of Approval (SOA) by the Carpet and Rug Institute (CRI), or WoolSafe.
The first approach is the weakest, but has had the support of rule makers since the early 1950s.
We have heard, but cannot support with credible sources, that most synthetic fibers (nylon) should be cleaned with products with pH readings of 10 or less. We have also heard, but cannot support, that wool should be cleaned with products with a pH range between 4.5 and 8.5. This is not pseudo-science. It is junk-science that not even Arrhenius’ theory would agree.
The IICRC S100, fifth edition, made a bold step in the right direction by saying this:
“However, since pH is but one limited measure of alkalinity or acidity of an aqueous solution and does not measure reactivity due to concentration, buffering and ionic strength, knowledge of pH alone is an inadequate measure of chemical and fiber compatibilities.”
This should imply that all rules restricting cleaning products solely upon their pH are in a transition from pseudo to junk-science.
One of the primary problems with this approach is it has often left out considerations for buffering.
To explain buffering, think of two armies facing off in a battlefield. One army is called “Acid” and the other is called “Alkaline.” The soldiers line up, face-to-face, in columns. The number of columns is the pH. The number of soldiers on each side is the total acidity or alkalinity.
Buffering is a part of Arrhenius’ theory, but it is under-emphasized. Thus, we have seen where a product’s original pH was 13.5 and it was safe for wool, then we have seen where products with a pH of 6.5 were too alkaline.
This may be confusing, but the reason (and according to Arrhenius) is that pH is measuring acidity, and not alkalinity. There is a general correlation between the pH scale and scale that measures alkalinity called the pOH.
If a pH of 6.5 is well-buffered, then it could have more alkalinity that a substance with a pH of 13.5. This was the case in a WoolSafe study that was published in 2004.
One can measure pH directly from the fiber with an electronic meter, and this resolves the problem of buffering. But there are no official guidelines setting definitive limits with this system.
The lack of rules for this approach, however, will not necessarily negate its power in litigation. There are charts to explain the meaning of pH readings.
The accreditation programs offer some official guidance. Plus, laboratory testing can assure considerations for buffering and reactivity.
However, the SOA is partially based upon the pH of the products.
WoolSafe has not, nor have any of the wool authorities, ever used the pH of a product as a definitive limit. Instead, WoolSafe has used buffering in their testing programs. Thus, the “4.5 to 8.5” rule reportedly from Wools of New Zealand was an example of junk-science.
Use real science
The bottom line is that measuring pH directly from the fiber is the noblest achievable goal based upon real science.
We must remember that nylon and wool are the two fibers most likely to need definitive alkaline limits.
- In most cases, wool should not be over a pH of 5.5. This would include before it is cleaned, during its cleaning, and afterwards. If wool’s reading is higher than this, its polarity will revert to its natural anionic state and it will no long have colorfastness with acid-dyes.
- It is just an educated guess, but nylon should not have a pH higher than 8. It needs a pH higher than 7 for detergency to reach a satisfactory level. Higher than 8 indicates that its stain resistance is likely damaged. Soil’s pH is generally from 6.1 to 6.7.
Therefore, the real choices are for either accreditation programs or meters. Cleaners need to challenge those who teach half-truths of the Arrhenius’ theory and demand a simpler applicable approach on understanding pH.
James (Jim) B. Smith is an IICRC-approved instructor and a senior practicing inspector. His educational studies come from Texas A&M University and the University of Houston. He has been in the cleaning industry since 1975. For more information, visit his website at www.carpetinspector.com/jbs or call (972) 334-0533 or (800) 675-4003.