Enough space must be left in the can when it is filled and sealed to allow some of the propellant to exist in its gaseous form, maintaining a constant pressure.
An inert gaseous compound under pressure. The propellant serves several purposes:
- It pushes the product out of the can
- It vaporizes after leaving the container, producing a spray or foam.
- In most cases, it also acts as a solvent for the product.
In the U.S., the most common aerosol propellants are liquefied gases, usually naturally occurring hydrocarbons such as propane or butanes. Approximately 10 percent of today’s aerosols use compressed gases, such as carbon dioxide or nitrogen, as propellants. While less expensive than liquefied gases, compressed gases are effective propellants only with certain types of products. Chlorofluorocarbons (CFCs) are not used in American-made aerosols, except for a few uses allowed by the U.S. Environmental Protection Agency. These exceptions, which are health and pharmaceutical products, represent less than one percent of the U.S. aerosol market and even these uses are being phased out as formulations with non-CFC propellants are approved as suitable alternatives.
A liquid blend of active ingredients, such as soaps or disinfectants, and inert ingredients needed to dissolve, dispense or stabilize the product. Because the aerosol container is hermetically sealed, the product is protected from contamination, evaporation or user contact. The aerosol delivery system often allows the product to be more concentrated and applied with more control than other packaging forms.
More than 80 percent of aerosol containers are made of steel with a thin coating of tin. The steel used to make aerosol cans contains about 25 percent recycled metal. Empty aerosol containers are as recyclable as other steel cans. The tin is recovered during processing, plastic components are consumed during reheating, and in today’s industrial-scale recycling facilities, small quantities of propellant or product left in the can present no hazard. Of the remaining 20 percent, most are made of aluminum, a small percentage are glass.
The curved shape of the can’s base counters the pressure of the propellant inside, and creates a “valley” so that all product can be reached by the dip tube and used.