How World War Two Brought
Us the Aerosol Can

How World War Two brought us the Aerosol can

An aerosol is a suspension of particles of a solid or a liquid in air or another gas. There are many examples of aerosols found in nature, including fog and airborne dust. Due to their suspension in gas, aerosols are transported finely and uniformly, making them perfect for many applications in cosmetics, manufacturing, and healthcare.

Developed in the 20th century, the aerosol can is a convenient handheld device that can produce aerosols in an instant. This revolutionized industries, birthing an industry that was valued at USD 10.24 billion in 2020. (1)

The development of the Aerosol can

Whilst the idea of using a pressurised canister to produce aerosols dates back to the 19th century, the first patent was awarded in 1927 to Erik Rotheim, a chemical engineer in Oslo. Rotheim developed a simple can and valve to wax his skis. (2) This however was not fully developed, and the aerosol can could not be put to effective use until WWII.

In the second world war, the US stationed many troops in the Pacific in an effort to combat the threat from Japan. Due to the harsh living conditions and unfamiliar tropical climate, they found themselves in, many troops died not from wounding but rather from poor sanitation, and insect-carried diseases such as malaria.

Whilst malaria was hard to treat, it could be prevented. Researchers from the US Department of Agriculture developed handheld canisters containing the insecticide DDT, and a liquefied gas known as a propellant.  These so-called Bug Bombs allowed soldiers to spray themselves and their surroundings with a thin layer of insecticide, protecting themselves from mosquitos. The solution was simple and effective, with over 50 million units being produced before the end of the war. (3) The Bug Bomb had all of the features of a modern aerosol can.

 

How it works

An aerosol can is a pressurized can containing two key ingredients – a concentrate and a propellant. The concentrate is made up of solid or liquid particles we wish to suspend in the aerosol, and the propellant is a liquidized gas, used to force the concentrate out of the canister.

 

When producing an aerosol can, the concentrate is liquid at room temperature so can be poured in before the can is sealed. The propellant on the other hand must be pumped in under high pressure afterwards. (4) This produces sufficient pressure that the content can burst out of the can in a controlled manner. 

An aerosol is a suspension of particles of a solid or a liquid in air or another gas. There are many examples of aerosols found in nature, including fog and airborne dust. Due to their suspension in gas, aerosols are transported finely and uniformly, making them perfect for many applications in cosmetics, manufacturing, and healthcare.

Developed in the 20th century, the aerosol can is a convenient handheld device that can produce aerosols in an instant. This revolutionized industries, birthing an industry that was valued at USD 10.24 billion in 2020. (1)

 be broken down into a few simple steps:

  • The propellant inside the canister can be found in a gaseous and liquid state. The gaseous propellant pushes down on the concentrate mixture, forcing it up the dip tube.
  • When the valve is opened, the liquid propellant now has room to expand, and so some propellant is converted from liquid to gas.
  • This results in an increase in pressure, forcing the concentrate through the narrow dip tube at speed.
  • Upon exposure to air, the concentrate evaporates to form an aerosol.

The consistency of the product expelled depends upon which propellant and concentrate are used, the ratio of propellant and concentrate, the pressure inside the canister, as well as the size and shape of the valve system. (5)

 So why is this simple design so effective?

The airtight nature of aerosol cans means their contents have a very long shelf life, and the concentrate’s properties will not change over the course of its lifetime. Aerosol cans are also impervious to contamination from bacteria and dust, making them great for keeping products sterile.

Perhaps their greatest advantage however of aerosol cans is their versatility; being able to dispense a huge range of products including gels, powders, foams, liquids and pastes. (6)

 

What can i use it for?

After the success of aerosol cans in WWII, a 1949 patent was given for the first mass -produced valve. This meant aerosols could be used in civilian products. The 50s saw a booming new industry of aerosols used in insecticides, hairsprays, deodorants and shaving foams. (7)

 Aside from cosmetics, aerosols are also used in manufacturing. The uniform spray makes aerosol canisters perfect for paint. A spray paint canister is much the same as any other aerosol can, but with the addition of a small solid ball called a pea. The pea is loose inside the canister and mixes the content when shaken.

The airtight valves of aerosol cans make them a perfect way to store oil. Lubricating oils such as WD40 are hence often found in these canisters.

Aerosols also play an important role in healthcare. Since they cannot be contaminated, aerosol cans are used to store disinfectants. These are often found in plastic containers called minsters, which work by the same principals as their metal counterparts. Some lifesaving treatments such as MDI asthma inhalers also work by aerosol technology.

A biological threat?

The development of aerosols however was far from plain sailing. When researchers first developed a simple spray can to fight malaria, no one would have guessed that not one, but two of the Bug Bomb’s key ingredients would be banned by the end of the century.

DDT

The insecticide DDT was found to be highly effective at killing mosquitos and combatting malaria. It played a vital role in the eradication of the disease in North America and southern Europe, but was much less effective in warmer climates where mosquitos bread all year round.    

It was later discovered however that DDT breaks down incredibly slowly meaning it remains in the environment for a long time. The insecticide kills most insects, not just mosquitos, and even birds. After its damaging effects on ecosystems were discovered, use of DDT was discontinued, and other pesticides were viewed more critically. (8)

CFCs

The propellants used in the Bug Bomb, along with almost all other aerosol canisters up until the 1980s, were chlorofluorocarbons – CFCs. These were chosen as they are nontoxic, nonflammable solvents.

Not until decades after their first use was it discovered that CFCs undergo reactions in the stratosphere, contributing to the depletion of the ozone layer. Without the ozone layer, there would be very little protection from harmful UV-B radiation, which causes skin cancers, and biological damage such as coral bleaching.

CFCs contribute to ozone depletion through the chlorine catalytic cycle:

  1. Ultra violet radiation causes a chlorine atom to break free from a CFC molecule. This atom is sometimes called a free radical.
  2. The chlorine atom reacts with an ozone molecule, to form chlorine monoxide and an oxygen molecule.
  3.  A free oxygen atom reacts with the chlorine monoxide, producing an oxygen molecule and a new free chlorine atom, so the process can be repeated. (9)

As a result of this discovery, 27 nations signed the 1987 Montreal Protocol to Reduce Substances that Deplete the Ozone Layer. Today CFCs are only used in limited medical products, with most aerosols containing the less reactive HCFCs or HFCs. (11)

Biological warfare

One threat from aerosol technologies that has not yet been fully addressed is that of Biological Warfare. In recent times, the threat posed by biological attacks has been realized. Aerosol cans would make a good delivery method of agents such as anthrax and allow discrete deployment. (12) Whilst bio warfare is largely forbidden, research continues, and these weapons have unknown destructive potential.

For better or worse

Aerosol cans are one of the most important inventions to have come out of WWII. They’ve brought about environmental controversy whilst making breakthroughs in healthcare and manufacturing, and revolutionizing cosmetics.

The adverse effects of the products, especially the CFC crisis, raise questions about when it’s appropriate to employ new technologies in physics before they are fully understood.

Aerosol cans however have adapted to criticism and today are much less environmentally damaging. With new amazing products such as the spray-on bandage continuing to emerge from this technology, it’s clear that aerosol cans improve people’s quality of life and continue to benefit us today.The development of aerosols however was far from plain sailing. When researchers first developed a simple spray can to fight malaria, no one would have guessed that not one, but two of the Bug Bomb’s key ingredients would be banned by the end of the century.

References

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