The Role of pH in Cleaning
By Aziz Ullah
When chemicals are dissolved in water, the mixture’s pH level can become either acidic or basic (alkaline).Vinegar and lemon juice are acidic substances, while laundry detergent and ammonia are basic. With a pH level of 7.0, pure water is neutral.
Acid and basic are two extremes that describe the property of a chemical, such as how hot and cold are used to describe the two extremes of temperature.
pH (potential of hydrogen) is the measurement of acidity or alkalinity of a substance when dissolved in water. Just as degree is used to measure precise temperature, pH gives us the precise measurement of acidity or alkalinity.
Mixing acids and bases can cancel out their extreme effects, much like mixing hot and cold water can “even out” water temperature. Extremely acidic or basic materials are called “reactive”, and can cause severe burns. Examples include automobile battery acid, which is very acidic, and drain cleaner, which is very alkaline.
Unlike the temperature scale, the pH scale is logarithmic. In other words, each number is 10 times more powerful or less powerful than the next, or preceding, number. The pH of 8 is 10 times more alkaline than the pH of 7, and the pH of 9 is 100 times more alkaline than the pH of 7, and so on.
Buffer solutions are equilibrium systems that resist changes in pH upon addition of an acid or alkaline.
A typical system may consist of a weak acid, such as vinegar (acetic acid), and its salt, sodium acetate. When a strong alkali such as caustic soda is added, the weak acid reacts with the strong alkali, forming more sodium acetate without a shift in pH.
In the cleaning industry, the term “buffer” is generally used to describe cleaning products that resist change in pH when diluting with water.
pH cleaning factors
Protein fibers (wool and silk) will tolerate the absorption of a limited amount of mild acid, and cellulose will tolerate a certain degree of alkalinity; however, both can be destroyed by strong acids and alkalis. Strong acids and alkalis can also adversely affect dyes.
What is most important is to maintain a pH level that effectively cleans the surface, without damaging dyes or fibers.
Olefin fibers can withstand a high degree of alkalinity. Solution dyed nylon, polyester and acrylic fibers can tolerate moderate alkalinity. Stain resistant nylon, wool and silk are more sensitive to alkalinity and should be cleaned in the neutral pH range.
The cleaning chemical”s pH value can have a direct effect on cleaning effectiveness. Each detergent formulation has maximum effectiveness at a specific pH value. For example, an acid solution is needed to remove metal oxide, such as rust, and an alkaline solution may be needed to clean a heavily soiled, solution-dyed olefin carpet in a rental unit.
A close-to-neutral pH is needed to clean wool, silk or stain resistant fibers.
Choosing the proper pH
The critical component in selecting a cleaner based on pH is how fast it needs to work.
Most cleaning chemicals are alkaline in nature, since hydrolysis (saponification), chelation and dispersion of soils typically occurs most effectively at alkaline pH levels.
Other factors, such as time, agitation and temperature play essential roles in the cleaning process. Although more detergency is achieved with longer times, more agitation and higher temperatures, this should be balanced against the damage these higher factors will do to the carpet or fiber.
The higher the pH level, the more corrosive the cleaner and the more damage it will do to pH sensitive fibers and dyes; hot temperatures employed in steam cleaning, together with higher alkalinity, makes it even worse.
Alkaline cleaners work best when soil can be hydrolyzed, such as kitchen grease containing natural oils and fats, natural greases, body oils and some proteins.
How fast can an alkaline cleaner damage a fiber? For dyes, the damage can be instantaneous and generally not reversible; the same is true with stain resistant fibers. With indicator-type dyes, the change may be reversible; for the fibers themselves, such as protein or silk, the damage will be slower, but corrective action must be taken immediately.
Oriental hand-knotted wool carpet undergoes harsh treatment during the washing and finishing in the manufacturing process, where luster is attained by use of caustic soda and bleach in the presence of a mineral acid. So there is no room for error as the carpet or rug may have gained the sheen, but as a result has become very fragile.
The following is a table showing what types of soil that can be cleaned at a certain pH.
|Type of cleaner
|Heavy oxide scales
|Inorganic salts, water soluble metal complexes
|Light oils, small particles
|Oils, particulates, film
|Oils, fats, proteins
Altering the pH of chemicals
If an attempt is made to lower or raise the pH (by using an acid or alkali) of the cleaning chemical without knowing the chemistry of a formulated product, the result can be counterproductive.
There could be ingredients in the product that only work at a particular pH, but may drop out, be rendered ineffective or may even hinder the cleaning.
The carpet or upholstery to be cleaned should be cleaned at the appropriate pH level that does not harm the fiber or the finishes.
If an alkaline product inadvertently is employed in cleaning wool or silk, the alkalinity must be immediately neutralized with a mild acid solution, such as a tribasic organic acid, which has three times the neutralizing ability of an alkali as compared to a monobasic acid. Moreover, being a mild acid, the chance of leaving the carpet or upholstery highly acidic is non-existent.
Aziz Ullah, Ph.D., MBA, is president of Fabpro Manufacturing, a formulator of carpet and upholstery cleaning products. He is a member of the American Chemical Society, senior member of the American Association of Textile Chemists and Colorists, and a member of The Textile Institute (UK). He can be reached at www.fabpro.com.