| Elizabeth
Connock B.Sc (Hons)
Abstract
Most additives to cosmetic and toiletry products are active ingredients
with functional properties. However, aesthetic appeal is also important
and there is a new trend of adding attractive particulate matter
to clear products for this reason. Some examples of this are the
addition of sparkle to bath foams, opal-like particles to shower-gels
and coloured seeds to exfoliating gels. These and many other materials
are described below together with example formulations for the supporting
ingredients and the techniques of ensuring stable distribution of
solid particles in liquid products.
Introduction
Until recently manufacturers took great care to avoid the presence
of particulate matter in cosmetic and toiletry products but now
(providing it is present by design!) it is seen as an attractive
addition. A previous paper [REF 1] described the properties and
use of physical exfoliants in personal care products. This paper
will concentrate on particulates that are added primarily for their
aesthetic appeal. Some particulates are manufactured specifically
for makeup, some are cosmetically acceptable particles from alternative
industries and there are others which are natural materials with
cosmetic appeal. Table 1 lists some of the principal types available.
Experimental
Unfortunately, incorporating particulate matter into liquid or
semi-solid products is not straightforward; there may be chemical
instability between base and particle, the particles may float or
sink over time, the particles may upset the balance of the preservative
system or they may be microbiologically contaminated. The particles
may also be too aggressive on the skin either through having sharp
edges or through being a potential allergen.
Previous work [REF 1] identified the importance of product yield
value in determining the resistance to movement of suspended particles.
The same paper also described the practical considerations of measuring
yield values and relating the physical attributes of exfoliants
to stability results obtained from centrifuge tests. This work has
now been extended to include the materials listed in Table 1. Clear
gels of different viscosities were required for the practical experiments.
From earlier trials it was found that gels prepared using an acrylates/C10-30
alkyl acrylate crosspolymer available as Carbopol ETD 20 had good
suspending properties and gave reproducible results. Gels were made
with Carbopol ETD 2020 at 0.25%, 0.50%, 0.75% and 1.00%, neutralized
with sodium hydroxide to pH 6.0 and used for suspending the test
materials. The samples were then centrifuged at 2,500 rpm and 5,000
rpm until the limits required to obtain stable suspensions were
found. The results are summarized in Table 2.
The tests showed that some materials floated, some sank and others
showed a tendency for partial floating or sinking. Evening Primrose
seeds separated into floaters and sinkers. The yield values of the
four strengths of gel were determined and are summarized in Table
3.
Stability at 5,000 rpm was marginal for many of the materials and
this is perhaps too rigorous a test. A number of samples that were
stable in a 0.50% Carbopol ETD 2020 gel at 2,500 rpm but not at
5,000 rpm was stored at 400C for three months to test the stability
of the preparations. In all cases the particles remained in stable
suspension. Therefore, if a system withstands centrifuge testing
at 2,500 rpm for 5 minutes it is reasonable to accept it as stable.
Results are summarized in Table 4.
Formulation
Knowing the Brookfield or Bingham yield values at which suspensions
are stable allows the formulator to design products with the minimum
viscosity necessary to achieve adequate shelf life. However, there
are other considerations to take into account for a successful formulation.
Solid particles may preferentially adsorb other product ingredients
and therefore upset the balance of the formulation. Preservatives
appear to be exceptionally prone to this phenomenon and so this
must receive careful evaluation at an early stage. Also, many particulates
of natural origin may harbour fungal spores and other microbial
contaminants. It is therefore important to evaluate carefully the
source of such a material and to secure confirmation that it is
not contaminated in any way. The most common methods of guaranteeing
such purity are treatment with ethylene oxide or irradiation.
Physical exfoliants are most commonly added to cosmetic emulsions
which form the basis of cleansing scrubs and masks but those that
have aesthetic appeal should be added to clear products in order
to maximize their attractive characteristics. Moisturizing gels,
shower gels and bath products are the most obvious product types.
Moisturizing gels may be applied either to the face or the body
and in the case of the latter the inclusion of a trace of subtle
glitter can give additional appeal to the skin after application.
Formula AEC 123 is a body moisturizer containing AEC Glitter Opal
(040) Hex, which catches the light as the bottle is moved. The moisturizing
properties are conferred by the glycerin content with the support
of sodium hyaluronate, which also improves the product's tactile
attributes.
Shower gels may include particulates for aesthetic reasons and
for their slight abrasive action. Formula AEC 125 contains AEC Luffa
Ground 30/100 which looks attractive, is pleasant to use and has
an obvious marketing appeal. Bath products may be bath oils or bath
foams, oils that foam or foams that feel oily. Adjusting the viscosity
and yield value of pure oil compositions is difficult to achieve
in production and adding sprigs of attractive foliage is the most
successful way of incorporating solid material into such products.
Surfactant based products are much easier to formulate and the addition
of a polymeric rheology agent such as Carbopol ETD 2020 greatly
increases their suspending power. Formula AEC 127 is a foam bath
with AEC Rose Petals Red (Whole) added for aesthetic appeal.
Footnote
Product clarity is important if the full visual effect is to be
achieved. Unfortunately Carbopol ETD 2020 does not have the sparkling
clarity of Carbopol 940 or 980 but the following hints may be helpful.
Prepare the initial gel and partially adjust the pH to 3.8 - 4.0
before adding surfactants and other ingredients and then complete
pH adjustment. The optimum pH for clarity appears to be 5.3 - 5.8
and potassium hydroxide is said to confer better clarity than sodium
hydroxide, which gives better clarity than amines.
The clarity of products containing surfactants may be further improved
by the addition of glycerin or propylene glycol. Lightly colouring
the product with a water-soluble, permitted dyestuff can further
enhance the appeal of the particulate. Eumulgin L is an excellent
solubilizer for perfumes in gel systems and 0.3 - 0.5% added to
the gel before neutralization often results in improved clarity.
Materials
Carbopol ETD 2020: BF Goodrich Performance Materials
Eumulgin L: Cognis
Germaben II-E: ISP
Uvinul MS-40: BASF
Particulates: All cited in this feature plus many others may be
obtained from A & E Connock (Perfumery & Cosmetics) Ltd.
Acknowledgements
Dr Mary Thornton, Creative Developments, for undertaking the experimental
work.
References
Ref 1 Connock, Elizabeth. B.Sc (Hons), "Physical Exfoliants",
Cosmetics & Toiletries Manufacture Worldwide 1999, pp. 37-43.
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