June 2019 SPRAY 33
Oxygen free radicals are capable of attacking various aerosol
ingredients. A favorite target is the double bond found in such
triglycerides as vegetable oils and some fatty animal products…
be reversed. The reaction is augmented by heat, light and traces of metal ions.
Of course, light is not a factor once compounds are in aerosol cans but tanks
of ingredients like vegetable oils (such as those used in cookware lubricants)
should contain anti-oxidants, be kept as full as practical and be well-covered
and protected from sunlight. Actually, sunlight contains about 52% infra-red
light and this has been reported as an initiator.
Various anti-oxidants are dissolved in susceptible ingredients for protection
against attack by oxygen free radicals. These ingredients can be vegetable oils,
but also fragrances, since almost all fragrances contain aldehydes. The antioxidant
works by very quickly reacting with the oxygen free radicals and changing
into a new free radical that is relatively stable. This
acts to break the possible reaction chain. They are used
very sparingly, usually at 0.01 to 0.02% concentrations.
Excessive use can overcome their protective action, allowing
oxidation to occur. Such uses may also be restricted
by regulatory authorities.
There are a fair number of anti-oxidants available.
They have different activities and thus offer protection
at different use levels. Several are proprietary or may be patented. Most are
complex organic compounds. Most are colorless liquid or solids, although the
tocopherols (such as Vitamin E) are red-brown powders. At their very lowest
use levels they have no effect upon the properties of the various aerosol products
that contain them. Some of the more well-known, popular anti-oxidants
are:
• BHA (Butylated Hydroxyanisole)
• BHT (Butylated Hydroxytoluene)
• Propyl Gallate (n.Propyl Trihydroxybenzoate)
• TBHQ (t.Butyl Hydroquinone)
• Topherol (Vitamin E)
• BHA/BHT Mixtures
BHA is popular, but not quite as effective as BHT. Both are water insoluble
but dissolve in many lipids. BHA is typically used at 0.02% of total formulas
and higher levels are strongly
discouraged by toxicologists.
BHT and its mixtures with
BHA are also recommended up
to 0.02%.
Propyl Gallate is usually at
least three times as effective at
BHA, BHT or their mixtures.
It has limited solubility in
lipids, but dissolves readily in
water and ethanol. It can form
colored complexes with iron,
nickel and chromium ions, but
not with aluminum ions. Most
chelating agents, such as EDTA,
tie up these ions if present and
augment anti-oxidant activity