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Name: Jo M.
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: 2002
Question:
Exactly how does an aerosol can work? I thought the material was compressed when sealed in the can and as the material is released from the can it would expand. I have students who think that the air has been removed from the substance and somehow gets "mixed" with the substance as it is being released from the can.


Replies:
The can contains both product and propellant. The propellant is basically a substance that is a gas at normal atmospheric pressure, but which condenses to a liquid at moderately higher pressures. When you press down the valve, some of the propellant turns to gas and carries some of the product out of the can with it in a fine spray.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

There is a whole aerosol can technology -- rather sophisticated too. There are several mechanisms: 1. In some cases the propellant is soluble in the medium. When the can is activated the propellant expands, ejecting the medium and foaming it at the same time. This is used in canned whipped cream (the propellant is NNO which is non-toxic and soluble in the cream. This is also used in "Edge" shaving cream (here the propellant is a propane/butane mix).

2. Another mechanism requires that the medium and the propellant are separated by a flexible bladder, with the medium on the top and the propellant on the bottom. When the can is activated, the propellant just "pushes" the medium out, but never actually mixes with it. 3. Yet another mechanism works on the principle of a Venturi pump in which the propellant sucks up the medium and they pass through a nozzle that atomizes the medium. Household insecticides often use this design. Of course the design of the nozzle becomes a whole technology depending upon the desired droplet size desired etc. These are only three examples of a rather complicated delivery technology.

Vince Calder


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