Lab Lessons—Wise Words From the Bench with Mukund Bhuta

By: Katie Anderson (Schaefer), Cosmetics & Toiletries magazine

Posted: June 30, 2011, from the July 2011 issue of Cosmetics & Toiletries.

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The price of petroleum products is rising—costing more than alcohol products—so manufacturers prefer to develop water-based aerosol products. [However,] creating a water-based aerosol formulation can be difficult. Chemists interested in water-based formulas therefore seek information on propellant selection, can lining, handling, valve selection, etc.

In addition, regulations on aerosols are becoming more strict because chemicals such as alcohol and new propellants have been found to affect global warming; in fact, in Europe, manufacturers have stopped using such propellant systems altogether. The US Environmental Protection Agency (EPA) is also trying to cut down on the use of man-made chemicals such as alcohol in aerosol cans. Any man-made chemical is an organic compound, and all organic compounds are volatile (i.e., alcohol). Currently, the EPA recommends formulating with only 55% volatile organic compounds (VOCs) in hair sprays, but the agency is considering reducing this number to 40%.

C&T: How does higher water content and lower alcohol content impact hair spray formulas?

When one uses too much water in the formula, the spray is wet—and consumers do not want wet hair when they use hair spray. This can be controlled by selecting the right combination of valve stem and opening system, the right actuator opening, or by inserting a vapor tap opening in the body of the valve.

C&T: What personal care products are difficult to put into aerosol form?

Powdered aerosol formulations can be challenging because the powder [i.e., talc] is not soluble in the propellant or any solvent, and the propellant is cold—its boiling point is less than zero. So when the propellant is put into the powder, the formulation cakes at the bottom of the can. Then when it is sprayed, the powder gets stuck in the opening of the valve and clogs. One therefore must use the right combination of propellant and anti-caking agents, which can be determined by the compatibility study.

C&T: What other components are important for the creation of an aerosol?

The internal varnish or the coating/lining of the can is important. Coating prevents the formulation from attacking the metal. Chemists must conduct complete compatibility studies (60 days at 45°C) to determine which lining should be used, and each and every lining should be tested; [one should not depend on the results from just one lining]. Both testing and experience can help chemists in choosing the correct one.

C&T: What was one of your biggest mistakes when working with aerosols?