The Science of Laundry Detergent

Welcome to science blogger Julian Taub, who is putting the science back into home economics. Check out the footnotes!

Posted by Julian Taub | Nov 22, 2011
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duboix/morguefile.comWe all love clean clothes: their smell, their look, their feel. We all use copious amounts of detergent each year. However, aside from watching commercial dramatizations, we pay little attention to how stains are removed. To understand how detergents work, you must first understand the factors that come into play while washing. You have the dirty shirt and a stain made up of a "compound" that chemically bonds itself to the shirt's fibers. Beyond that, charged metal particles like sodium, calcium, and iron are floating around the water you wash your clothes with, which can make your cleaning agent less effective.(1,2)

How detergent "ecosystems" remove stains

A detergent should not be seen as one substance, but its own "ecosystem" that affects the space where the water comes in contact with the clothing, to effectively remove stains. Most detergents have 7 different components working together. Surfactants (short for "surface actants") act as "emissaries" between the water and stain areas, easing the tension between the two, eventually enveloping and dissolving the stain.(2)

Enzymes break down stain molecules into smaller components. Builders bond with the metals in the water, so that the surfactants can work efficiently. Polymers catch dirt in the water, making sure it doesn't settle back on the clothing. Lastly, bleach destroys molecules that produce color,(3) optical enhancers absorb UV light and release the light that is the color of the shirt (to brighten),(1,4) and lye or ammonia keeps the pH balance steady.

Detergent is all about balance

Just like Eastern philosophy, detergent is all about balance. The pH and the amount of surfactants or enzymes in the product all play a key role in its effectiveness. Too few surfactants won't get out the stain, and too many will leave a residue on your clothing.(2) Although reading the clothing label washing instructions and detergent package directions  is common sense, it's also important to set the right balance for the laundry. You might find it hard to gauge what percentage of a specific chemical is being used for the cleaning, so I would suggest improvising and adjusting the water amount, temperature, and detergent concentration, depending on your results for different loads.

Phosphate vs non-phosphate detergent

You've all probably heard about phosphate versus non-phosphate detergent. Both can be used in the same way. Phosphate, a phosphorous-based salt sometimes used as a surfactant, is one of the key ingredients to life and is non-toxic. However, the problem is that when the phosphate enters the outside world it likes to promote life ― sewer and river life. It helps cells like blue-green algae grow exponentially, killing off fish populations in rivers.(5) To avoid this, many companies now use a synthetic surfactant called zeolite, which is not as effective without the help of other chemicals.(6) Phosphorous can be recycled, but a very small percentage is removed from sewage treatment (although some countries in Europe have been working on this).(7, 8) If you're environmentally conscious, you should steer clear of phosphate detergents. 








8.      Phosphates, The Only Recyclable Detergent Ingredient. Centre Européen d'Etudes des Polyphosphates. July 2007. 

Julian Taub is a Networx writer. 

Updated February 27, 2018.

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