Aerosol Products

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Panel: Steve Risotto
Media: Sarah Scruggs

Aerosol sprays are a popular and convenient way to dispense a wide variety of products. In part because they are so easy to use, provide a targeted stream that reduces waste, and are able to reach both large and small spaces effectively, it is not surprising that aerosols are used for coatings, cleaning agents, air fresheners, personal care items, insecticides and a host of other products. A key part of many aerosol sprays is solvents, which help improve product performance and extend shelf life – this means that sprays remain effective and last longer.

How do Aerosol Sprays Work?

Aerosol products are a mixture of liquefied gas, propellant, solvent(s) and active ingredients that are packaged under pressure in a container with a valve. When the valve is opened, typically by pressing a button on the top of the can, the internal pressure forces the aerosol up the dip tube and out of the valve. Many aerosol products require shaking before use to completely mix the ingredients prior to spraying. Failure to do this can mean the propellant (part that helps push the ingredients out of the can) would be used first, which would then trap the remaining ingredients in the can.

Role of the Solvent

Choosing a solvent or solvent system that meets performance needs is not always as simple as it seems. The primary function of solvents in aerosol products is to keep the entire formulation evenly mixed to assure the proper ingredient proportions of the product are the same throughout its use. Encouraging even mixing also helps extend the life of the product, so a paint spray, for example, will be as usable today as it was a few weeks before. 

Recall that the aerosol formulation contains three major components: propellant, solvent, and active ingredients. Most propellants have poor solvency characteristics so a solvent is used to couple the active ingredients into a solution with the propellant. A second solvent with a function of holding the active ingredients in solution may also be used.

Another important function of the solvent is to help produce a spray with a particle size that is most effective for the particular application involved since different spray characteristics are needed for paint, shaving cream, and insecticides. For example, air fresheners are designed to come out as a fine mist because no one would want to spray an air freshener that left large, wet droplets on furniture and curtains. The ability of the solvent to reduce the vapor pressure of the propellant affects the particle size of the spray.

In some cases the solvent is essential to the performance of the product itself. Take spray painting, for example.  Many spray paint formulations contain fast, medium and slow evaporating solvents.  The fast evaporating solvent provides a lower initial viscosity to make application easier; the medium evaporating solvent helps prevent dripping and sagging and the slowest evaporating solvent, the last to leave the system, finalizes flow and leveling to promote a uniform film thickness and ensures the paint sticks to the substrate.

As you can see from the examples above, solvents help aerosol products in a variety of ways. They hold the formulation together in the can, they help maintain the right particle size for the application, and can even lend important performance characteristics to the product itself. From personal care items to household products and beyond, modern solvents make it happen! 



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