Anti-oxidants in personal care products act to prevent oxygen
free radicals from creating rancidity and other malodors due to
their chemical action on lipids with double bonds, aldehydes
and other susceptible ingredients used in these products…
in general. EDTA is ethylenediamminetetraacetic acid,
presented as one of its sodium salts; i.e. Na2EDTA.
Another useful chelating agent is HEDTA: hydroxyethylenediamine
triacetic acid and its sodium salts.
TBHQ is unquestionably the gold standard
of anti-oxidants. It is more effective than
the others by a factor of at least three times.
Known for over 30 years, it can be safely used
at 0.10% of the entire formula, but excellent
results are obtained at 0.01%. It has limited
water solubility, but dissolves easily in lipids.
If a natural anti-oxidant is needed, one can
select d.tocopherol or its counterparts, like
delta-tocopherol. Beside the intense color
problem, the tocopherols are quite weak as
anti-oxidants. As such, they may be incorporated
at about 1.00% to achieve reasonable
activity.
Concentrate batches containing tocopherols
are adversely affected by light and should
always be covered with a tight-fitting metal lid. Ingredient listings on aerosol skin
care and other products sometimes list Vitamin E and Vitamin C Palmitate. This is
because the latter can act as a strong synergist to increase the activity of tocopherols. In fact,
Vitamin C Palmitate can also synergize other anti-oxidents as well.
Formulation Aspects
When including fatty acids or their triglycerides for aerosol products, formulators will often
select ingredients where components with double bonds are
essentially absent. For example, palmitic acid can now be
purchased in very pure forms, where the oleic and linoleic
acids have been removed by the use of vacuum distillation or
other techniques. This can eliminate the potential problem
of double bond attack by oxygen free radicals. However, antioxidants
may still be needed to deal with other unsaturates,
aldehydes and sensitive ingredients. It is prudent to test ingredients
and finished concentrates for peroxide value. This will
indicate if any free radical chain reactions have been initiated
and if so, how far along they may have progressed. Products
can usually be accepted if the peroxide value is 5.0
or less. However, if the value is over 10, the antioxidant
additives would be overwhelmed and
the product should be rejected.
If the product gives an intermediate result,
between 5.0 and 10, tests can be made
using maximum levels of the desired
anti-oxidants in aerosols where the available
tramp oxygen is reduced by vacuum
crimping. After about two weeks storage at
100°F (37°C), the product may be retested
for peroxide value. Hopefully, it will have
diminished or at least stabilized. A quality
34 Spray June 2019