Since about 1959, when very economical, “water-based,” w/o air fresheners and insecticides were developed
(F.D. Haase, Danville, IL), these emulsions have been used worldwide in well over a billion aerosol
dispensers to date. Their popularity has been considerably diminished in the U.S., due to the impact
of VOC/MIR (maximum incremental reactivity) regulations developed by the California Air Resources
Board (CARB) that have had the effect of arbitrarily reducing the percentage of hydrocarbon propellants
to the degree where the spray quality has been adversely affected. The industry has reacted by developing
“nitrosol” (nitrogen propelled) versions, sometimes boosting the hydrocarbon propellant content with
HFC-152a (1,1-difluoroethane) and other means.
These steps have redirected attention to spray characteristics. Ideally, when the dispenser is briefly
shaken and pointed upward, there should be essentially no particulate “fall out.” Formulators consider
such factors as particle size, possible tiny foam clusters, spray distance to polished wood furniture and (of
course) the formulation. The concentration of non-ionic emulsifiers, fragrances, possible odor counteractants
and any corrosion inhibitors should be kept as low as possible. As little as about 0.13% low-HLB
non-ionic emulsifier can be used successfully. By using containers that are fully lined or laminated, the
usual 0.15%–0.20% of sodium benzoate corrosion inhibitor can be eliminated. The essential oil blend
(fragrance) must be selected with care to avoid ingredients with strong colors or solvent properties. Those
ingredients that meet VOC criteria may warrant minimization if practical.
If the VOC content is to be limited to 20% (in the U.S.), one option is to use a blend of about 20%
n.butane and 5% or more of HFC-152a, since the latter is a non-VOC (all blends of n.butane and HFC-
152a have air-free pressures of 179 or less at 130°F). As is often the case, formulators must balance cost
and performance. SPRAY
January 2020 SPRAY 31