Detergents and soaps
by Chris Woodford. Last updated: January 24, 2012.
When you're young, "bathtime" is
another word for "torture" and a
harmless block of soap can seem like an offensive weapon. Fortunately,
most of us soon grow out of that little problem and learn to recognize
soap and water for what they are: a perfect way to shift the daily grime.
Soap seems like the simplest thing in the world. Just splash it on your face and it gets
rid of the dirt, right? In fact, it's quite a cunning chemical and it
works in a really interesting way. Let's take a closer look!
Photo: Some typical household detergents. All
of them, except for the soap, are liquids. Environmentally friendly detergents, such as those
produced by Ecover, are made with plant-based ingredients to reduce their environmental impact.
What are detergents?
Often we use the words "soap" and "detergent" interchangeably, but
really they're quite different things. A detergent is a chemical
substance you use to break up and remove grease and grime, while soap
is simply one kind of detergent. Soap has a long history and was
originally made from purely natural products like goat's fat and wood
ash. Today, detergents are more likely to be a mixture of synthetic
chemicals and additives cooked up in a huge chemical plant and, unlike
traditional soap, they're generally liquids rather than solids.
Detergents are used in everything from hair shampoo and clothes washing
powder to shaving foam and stain removers. The most important
ingredients in detergents are chemicals called surfactants—a word made
from bits of the words surface active agents.
Photo: Soap: the detergent we know best. This one
describes itself as "pure" because it contains no added chemicals or perfumes.
How surfactants work
You might think water gets you wet—and it does. But it doesn't get
you nearly as wet as it might. That's because it has something called surface tension. Water molecules prefer their own
company so they tend
to stick together in drops. When rain falls on a window, it doesn't wet
the glass uniformly: instead, it sticks to
the surface in
distinct droplets that gravity pulls down in streaks. To make water
wash better, we have to reduce its
surface tension so it wets things more uniformly. And that's precisely
what a surfactant does. The surfactants in detergents improve water's
ability to wet things, spread over surfaces, and seep into dirty
clothes fibers.
Surfactants do another important job too. One end of their molecule
is attracted to water, while the other end is attracted to dirt and
grease. So the surfactant molecules help water to get a hold of grease,
break it up, and wash it away.
What other chemicals are in detergents?
Surfactants aren't the only thing in detergents; look at the
ingredients on a typical detergent bottle and you'll see lots of other
chemicals too. In washing detergents, you'll find optical
brighteners (which make your clothes gleam in sunlight). Biological detergents
contain active chemicals called enzymes,
which help to break up and
remove food and other deposits. The main enzymes are proteases (which
break up proteins), lipases (which break up fats), and amylases (which
attack starch). Other ingredients include perfumes
with names like "limone", while household cleaning detergents
contain abrasive substances such as chalk to help scour away things
like burned-on cooker grease and bath-tub grime.
Photo: Soap and water can clean almost anything thanks to detergent action. Photo by Joshua Scott courtesy of US Navy.
A brief history of soaps and detergents
- 600BC: Historians think people have been making soap for around 2000 years, even since the time of the Phoenicians (an early
Mediterranean civilization).
- 1790: Soap remains an expensive luxury until French chemist Nicolas
Leblanc (1742–1806) finds a cheaper way of making it using salt.
- 1800s: Soap-making becomes popular in the United States and North America, where people mix the ingredients in large "soap kettles".
Soap kettles are used for most soap-making until World War II.
- 1916: German chemist Franz Gunther develops the first surfactant for detergents from coal tar.
- 1930s: Detergents based on surfactants are introduced in the United States.
- 1950s: Synthetic detergents are developed to counter soap shortages caused by World War II and soon overtake traditional soap to
become our favorite chemical cleaners.
- 1960s/1970s: Concerns about water pollution from detergents building up
in rivers and seas lead to the development of the first biodegradable surfactants.
Further reading
On this website
On other sites
- The American Cleaning Institute (ACI): Formerly the Soap and Detergent Institute, but still representing the manufacturers of cleaning products. Includes educational resources, and information on environmental impacts of detergents and sustainability.
- Taking the water out of detergent: BBC News, 4 February 2009. Unilever chemist Richard Craven shows how to make concentrated clothes washing detergent in a laboratory, going through all the ingredients step by step. Amazing how many different ingredients there are!
Articles
Books
- Handbook On Soaps, Detergents & Acid Slurry by Niir Board. Delhi, India: National Institute of Industrial Research, 2006. A detailed book about the manufacture of detergents and soaps, and their chemical ingredients.
- Soaps, Detergents, and Toiletries by P. K. Chattopadhyay. Delhi, India: National Institute of Industrial Research, 2003. Another detailed volume covering everything from shaving foam and after shave to tooth paste and hair shampoo. Covers manufacturing and testing processes and chemical ingredients.
- Green Cleaning for Dummies by Elizabeth B. Goldsmith and Betsy Sheldon. New York: Wiley, 2008. Considers the environmental impact of cleaning products and how you can clean in greener ways.
