Thousands of chemists and technicians are currently hard
at work to improve or create emulsion products. Emulsion
technology is wide-ranging and often complex, but it is
rarely taught in universities and product development
chemists must educate themselves...
Brookfield Viscometer
For those who wish to do so, the ungassed BOV concentrates can be
measured for viscosity by using a suitable Brookfield Viscometer. However,
measuring the “puffing gassed” aerosol counterpart is more difficult. So
far, highly reproducible results have remained elusive.
Emulsion destabilizers
This is a larger field than the stabilizers, since it includes de-frothing
agents in the food industry and many others. Aerosol uses include the
de-foaming of spray starch deposits on textiles, “quick-breaking” foams and
the de-foaming of water-based paints. Kenneth Klausner of The Mennen
Co. patented aerosol quick-breaking foams in about 1955. They have recently
gained added importance as hand sanitizers in the war against COVID-19
infections. Labels promise to kill 99.99% of coronaviruses and related microorganisms.
Their cidality is due to an ethanol-water composition in which the
ethanol content also destabilizes the emulsion when the foam is briefly rubbed
onto warm hands. A typical formulation can be seen below.
Some of these products are
fortified with such disinfectant/
deodorants as Polyquaternium
6, Clotrimazole and Poltquaternium
8. Others may be lightly
gelled with xanthan gum (Kelzan
C), carbomers (Carbopol 934)
or other thickeners. If a quickbreaking
foam is of little interest,
then pump-action and other hand
sanitizers are readily available. All
should be approved by the U.S.
Food & Drug Administration
(FDA).
Misunderstood
Emulsion technology is an important aspect of most aerosol formulation work, yet it is poorly understood
by many workers, leading to wasted time and frustration. Among the many pitfalls is the problem
of emulsion instability. There are many ways to deal with this common phenomenon and a number
of them are discussed here. They include selecting secondary emulsifiers, adding gallons of insoluble
powders, strengthening the interstitial surface of dispersed particles and adding energy to the system by
homogenization.
Prospective aerosol emulsions must be tested for stability. This is done by packaging them in clear,
pressure-resistant glass and letting them age for months at, for instance, 70°F and 100°F. The formulations
must also be tested in the proposed can since traces of multi-valent metal ions can sometimes be
ruinous.
It is hoped that this brief article will persuade chemists to advance their knowledge of emulsion technology
and emulsion stabilization, in particular. Spray
26 Spray January 2021
QUICK-BREAKING AEROSOL FOAM
Ethanol (Anhydrous) 55.665
Seionized Water 38.100
Polawax NF 1.850
Sodium Benzoate (Corrosion inhibitor) 0.190
Sodium Sesquicarbonate 0.095
Fragrance (Optional) 0.100
Iso-butane A-31 1.700
HFC-152a (1,1-Difluoroethane) 3.300