storage at 120°F. Afterward, the odor of the aged product is compared with that
of freshly made samples. A trained perfumer will generally be able to detect
differences and determine if they are important. Perhaps surprisingly, the aged
samples may have better fragrances than the fresh ones. This is the case with
ylang ylang.
A Sophisticated Response
The effects of air (oxygen) on aerosols requires a sophisticated response in
both formulation and testing. There are other oxidants in air, such as ozone
and nitrogen dioxide, but they are in trace amounts and can be neglected.
The pressures of aerosols are the sum of the partial pressure of the product and
partial pressure of trapped air. In rare cases, the true pressure may exceed the
U.S. Dept. of Transportation (DOT) design pressure limit of the dispenser. Vacuum
crimping is suggested for virtually all aerosol units. Although this may have only a very
minor effect on corrosion possibilities, it can lead to more constant delivery rates and spray
patterns as well as reduced pressures. The frequent laboratory practice of completely displacing
trapped air with a stream of propellant gas leads to aerosol samples with properties that cannot
be duplicated in production.
Some aerosol ingredients are air (oxygen) sensitive. Others are moisture sensitive. They should
be stored only in well-filled, tightly closed containers of compatible materials, held upright in
cool areas. Displacing the air from partly used fragrance drums with nitrogen or argon may be
beneficial if the blend includes air-sensitive ingredients. Trapped air (oxygen) will be a technical
consideration for aerosols into the foreseeable future, complicating the product development and
production programs. SPRAY
March 2018 SPRAY 47
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