Ph.D in Detergent pH
By George Weise
A Basic 'Chemistry 101' Primer on Using Today's Advanced Cleaners
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with basic soap is defined by molecular activity. Hydrophilic molecules are attracted to water while hydrophobic molecules are repelled. The phenomenon of wetting occurs where the surface tension of water is broken down allowing it to penetrate various surfaces during cleaning. Without this action, water would bead up and could not saturate a surface. Additional surfactants in detergent accelerate the breakdown of surface tension and help detergent cleaners to penetrate soil faster and deeper than basic soap. We like to say that they make the water wetter.
Modern surfactants have added different ionic charges to detergents. Surfactants are divided into basic types: anionic (negative), cationic (positive) or non-anionic (neutral). In rare cases, an amphoteric surfactant, which has both positive and negative charges, may be used.
Matching surfactant to cleaning challenge
Knowing what type of surfactant a cleaner has may be necessary for effective application. For example, using products together where one has an anionic charge and the other a cationic charge will create reverse saponification. Saponification occurs when a high pH comes in contact with oil or grease and produces soap. Remember, basic soap is a mixture of oil and hydroxide. Alkaline builders help saponify and emulsify grease and oils from the surface. Emulsification also helps remove oil and grease that did not saponify by suspending dirt in a form of tiny droplets. Reverse saponification results in a gummy, messy residue that can become difficult to remove and attracts dirt.
Using a cationic cleaner, which includes most disinfectants, will cause carpets to release the carpet protectant. This happens because the carpet protectant has a negative charge to help it repel acids. A cationic cleaner features a positive charge. It will attract the negative charge from the carpet protectant and will help to neutralize it.
Modern detergents also have added alkaline builders. These boost the detergents cleaning effectiveness; they separate minerals to soften the water, making the detergent more effective.
Alkaline builders are not cleaners. They must be combined with surfactants because they have virtually no wetting properties on their own.
Some detergents also have added solvents. A solvent is a substance that will dissolve other substances. Solvents are added because after the alkali builders saponify grease and oil, they start to oxidize and become hard to remove.
The solvent inhibits this process and provides an added emulsification process for oil and grease. This keeps oil and grease separated so they will not recombine. This type of solvent is generally a glycol base.
Since most dirt is acid, the alkaline in the detergent makes it a good cleaner for common dirt. For detergents to be effective most need to have the proper pH (percentage of hydrogen) which measures acidity and alkalinity. The scale goes from 0 to 14. Seven is halfway and is neutral. It is the balance between acidity and alkalinity. A solution that is acid will read 0-6 on the scale (6 being weaker than 1) and a solution that is alkali will be 8-14 on the scale (8 being weaker than 14).
Each number on the scale is a 10-fold difference from the adjacent number. For example, a pH of 5 is 10 times as acid as a pH of 6; a pH of 3 is 10 times the acid of 4 and 100 times as acid as 5. Different cleaners have different pH factors.
pH is very important in cleaning. Too strong a pH can damage surfaces, remove floor finish, as well as damage or discolor carpet fiber. It also can weaken carpet protectors.
Using an acid cleaner to do general cleaning will be of little value since most dirt is acid. The reason most shower cleaners are acid-based is because the soap residue is alkaline. Most general cleaning should be done with a pH of 9 and no more than 10. Anything stronger may damage surfaces and possibly void carpet warranties.
Cleaning challenge dictates pH factor
To choose the right chemical for cleaning, determine the type of dirt to be cleaned. This will help decide the degree of pH needed, either alkaline or acid. A greasy surface will need a stronger pH than one that has dirt on it.
What is the surface that is being cleaned? Is it a carpet? If so, what type of fiber is it? Fiber type is very important in determining pH needs. Does the surface have a floor finish? A neutral pH is needed. A pH that is not neutral will damage floor finish. Will the surfactant interfere with or cause reverse saponification if used in conjunction with other products? Some surfactants cause products to foam and bubble up.
A high pH used to be very important for a detergent cleaner to clean well. With new surfactants and added solvents it is now possible to use a pH level that is close to neutral and still clean better than the high pH cleaners of old. This makes it easier on the person cleaning, it is a safer product to use and it has far less residue and will not damage surfaces.
George Weise is superintendent of custodial services at the University of South Carolina.