Builders and water softening
The ingredient that makes the surfactant work by getting the calcium out of the way. It is why the same detergent performs differently in two towns.
In detail
Hard water carries dissolved calcium and magnesium, and those ions interfere with cleaning in two ways: they react with soap to form an insoluble curd, and they reduce the effectiveness of many surfactants. A builder is an ingredient added to a detergent specifically to deal with them, by binding the ions into a soluble complex — sequestration — or by exchanging them for ions that do not interfere. Phosphates did this job for decades and have been restricted in many countries on environmental grounds; citrates, carbonates, silicates and zeolites do it now. The idea explains a set of otherwise unconnected observations. A detergent that works well in Glasgow can underperform in Cambridge, because there is more hardness to consume before any surfactant is free to clean. A dishwasher has a salt reservoir because it softens its own water by ion exchange, and running it empty is why glasses film and etch. Trisodium phosphate is described by a regulator as a water softener and a detergent ingredient in the same sentence, which is the clearest statement of the dual role. And citric acid works on limescale partly by chelation as well as by acidity.
Why
- Trisodium phosphate is explained by Builders and water softening
- Laundry detergent is explained by Builders and water softening
- Dishwasher salt is explained by Builders and water softening
- Zeolite is explained by Builders and water softening
- Polycarboxylate is explained by Builders and water softening
Sources for this page
Sources
Handbook of Detergents (Surfactant Science Series)
CRC Press / Taylor & Francis · Reference work
Relied on for: That water hardness reduces detergency through interaction of calcium and magnesium ions with surfactants, and that builders and chelants are used to address it. (background and mechanism only)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Right to Know Hazardous Substance Fact Sheet: Sodium Phosphate, Tribasic (RTK 1724)
New Jersey Department of Health · Government or regulator
Relied on for: That trisodium phosphate is used as a water softener and in detergents. (states this directly)
Verification: a person has read the passage relied on.
Read on — The 'IDENTIFICATION' paragraph and the 'HANDLING AND STORAGE' reactivity list. Supports the claim as stated. Adds the alkaline builder family to the agent records, and gives the catalogue a fourth independent regulator statement that alkalis attack aluminium — which is now sourced from sodium hydroxide, potassium hydroxide, trisodium phosphate and sodium carbonate rather than from one sheet.
Last reviewed by a person on .