In the first and second parts of this series, we waxed nostalgic about the history of aerosol products and explained how the packaging works. In Part 3, we talk about the stuff inside the can. There are two basic parts to an aerosol formula: the formula, which is a liquid concentrate, and the propellant which is a gas.
What’s in the formula
The concentrate contains the goodies that makes the product function. If it’s a hair styling product like a hairspray or mousse, the goodies are resins that hold your hair in place. If it’s a breath freshener, the goodies are flavoring agents, and if it’s a depilatory, the goodies are the active ingredients that dissolve your hair. The goodies will vary from product to product, but they give the product its basic functionality. They’re the reason you buy the product in the first place.
In addition to the goodies, the concentrate contains other ingredients like, solvents, fragrance, pH adjusters, anti-corrosion agents, and a bunch of other chemicals that we won`t bore you with right now. All you really need to know is that the concentrate is what makes the product do what`s its supposed to.
What Is A Propellant
Propellant is a general term for any gas that propels the concentrate out of the can. There are several different types of gasses used as propellants, most of which are liquefied gasses. That means when the gas is under pressure it converts to a liquid. If you’ve ever seen a tank of propane gas used on a home BBQ grill, then you know what we’re talking about. If you shake a tank of propane, you can feel it slosh around inside because it’s a liquid. But if you open the valve on the tank: whoosh- the propane comes out as a gas. That’s exactly how an aerosol works. Except in an aerosol the gas is mixed with the product concentrate (remember those goodies!) and the valve on the can is designed to release the product as a spray or a foam.
4 Types of Propellants
1) Propane represents one of the types of gasses used in certain kinds of aerosols. This type of propellant is known as a Hydrocarbon which is also referred to an LPG or Liquid Petroleum Gas. These gasses work very well in aerosols because they’re soluble in alcohol and other solvents used in products like hairspray. However, they are very flammable and they have recently come under fire for contributing to air pollution. In fact, in the US, hydrocarbons are no longer used a primary propellants but they’re still commonly used in other countries.
2) Chlorofluorocarbon (or CFCs) were popular propellants before hydrocarbons. These gasses have low flammability and good solvency, but they were banned from conventional aerosol use in the late 1970s because of fear they were damaging the ozone layer. Once this environmental problem was identified, the aerosol industry rushed to remvoe CFCs.
3) Hydrofluorocarbons (or HFCs) have many of the good properties of CFCs but they don’t affect the ozone layer. If you pick up an aerosol today you know it contains an HFC if it lists 1, 1-difluoroethane or Propellant 152a on the label. HFCs are particularly useful in hair sprays because they allow the creation of formulas without any water. (Water in a hair spray is a bad thing!) So hairsprays containing 152A are the best on the market. Unfortunately, while these propellants are almost technically perfect, they are very expensive so not many companies use them.
4) Dimethyl ether (or DME) is the only propellant that is miscible with water, which allows it to be used in lower cost formulations. While DME is an excellent propellant, adding water to a product like hairspray, can severely affect the way it works. Hairsprays become sticky, slow drying, and make your hair style droop. If you’re shopping for an aerosol hairspray you should really avoid any product that lists water as an ingredient.
Ok, now that you know the fundamentals of aerosol packaging, formulas, and propellants, next time we’ll explain how they all come together to make a finished product. See you back here for Part 4 of Adorable Aerosols!