Cationic polymers + anionic thickeners

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Mussarrat Noor
on cationic polymers
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PRODUCTION INGREDIENTS
Cationic polymers + anionic thickeners …
Cationic polymers can provide skin care formulations with
novel benefits, but they are often difficult to work with for those
unfamiliar with the need to adjust for their charge properties.
C
ationic ingredients are widely
used in hair care and rinse-off
products. Gradually, cationic
emulsifiers, surfactants, emollients,
and polymers are also making inroads into skin care formulations.
Consumer brands such as Curél,
La Roche-Posay, Maybelline, Elizabeth
Arden, and others have utilized
cationic ingredients in some of their
formulations, but the use of such
ingredients in skin care is still in
its formative stages, particularly for
cationic polymers.
Many cationic polymers were in fact
specifically designed with hair care in
mind and therefore provide limited
performance and sensory benefits for
skin. In some instances, however, this
lack of use is an outcome of unfamiliarity by formulators as to how they can
employ cationic polymers within skin
care formulations that contain anionic
ingredients. New offerings, including
Air Products’ Deposilk Q1 polymer, are
addressing these limitations by making available cationic polymers more
attuned to skin care formulations.
Cationic ingredients, being widely used in hair care and rinseoff products, are gradually making inroads into skin care formulations
Drawbacks of cationic-anionic interactions
Cationic-anionic interactions can generate the formation of
precipitates as well as lead to a loss in viscosity and other
undesirable traits. Use of cationic polymers and anionic
surfactants is common in rinse-off products, particularly in
2-in-1 shampoo/conditioner products. These products can
exploit differences in and interactions by these two types
of ingredients to provide both cleansing and conditioning
benefits. But whereas the rinsing and dilution characteristics of such products enables cationic and anionic elements
to serve complementary purposes, the leave-on nature
of most skin care products can pose greater challenges to
cationic-anionic combinations.
COSSMA 12 I 2011
Formulating with anionic
thickeners
Anionic thickeners are commonly used
in skin care leave-on products, and for
cationic materials to be employed
more widely within skin care, they
must easily compatibilize with such
systems. General guidance on how to
formulate cationic polymers into anionic-containing formulations is limited. Vondruska, for instance, describes
a general method for compatibilizing
cationic materials with anionic thickeners through first complexing the
cationic material with an anionic complexing agent1. More common are ma-
terial-specific procedural or formulation modifications that must be used
to enable incorporation of cationic and
anionic ingredients. For instance, in
their patent application, Maubru et al.
seem to suggest that use of copolymer
of methacrylic acid and alkyl acrylate, a
funtionalized silicone, and a cationic
polymer can be employed in a formulation containing anionic surfactants2.
Skin-focused cationic
polymers
The recently launched Deposilk Q1
polymer from Air Products provides an
example of a cationic material specifically designed for skin that can be successfully incorporated across several
different anionic-thickener-based skin
care systems. Using the new polymer
with anionic thickeners does entail
some minor formulation-specific procedural modifications, but these are
generally not as demanding, particularly since they involve procedural rather
than formulation-specific changes.
As a skin-focused material, this
polymer also provides more appropriate performance benefits for skin care.
For instance, most hair-care focused
photo: Air Products
Foto: La Roche-Posay
… formulated for skin care
Cationic material can be successfully
incorporated across several different
anionic-thickener based skin care systems
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Cationic polymers: a key challenge in skin care
A key challenge when using cationic polymers in skin care is their
charge. For leave-on products, cationic and anionic elements must
compatibilize and perform as they stand, without exogenous effects
induced by water washing. General factors, such as use-level concentration and charge density of the cationic or anionic materials,
can contribute to cationic-anionic compatibility within formulations.
Material-specific factors can also play a role; for instance, a polymer’s overall charge may itself be a balance of anionic-cationic
charges rather than strictly unipolar. Formulators planning to utilize
cationic polymers in their skin care systems need to be aware of
charge-related interaction potential before formulating.
polymers are designed to provide a strong slip sensory profile;
this is of course suitable for hair conditioning requirements but
can feel inelegant on skin. In contrast, the new polymer provides
a light, silky feel that can be more appealing for skin care products. Moreover, it shows very low irritation potential based on
in-vitro skin and eye tests, addressing another common concern
related to hair-care focused cationic materials. It is also able to
address the wider diversity of skin care by having compatibility
and deposition effectiveness across a wide variety of ingredients
as well as by being soluble in water, oil, glycols, and alcohols.
To use the new polymer, formulators can select from five different procedural modifications dependent upon the type of anionic thickener employed in their system and upon the nature of
their scale-up or production processes (see Internet box). In
general, these procedures describe how and when the polymer
is added into the system. The basic approach involves pre-dispersing the polymer in a separate water phase and slowly combining this water phase with the thickener-containing phase.
Underlying the effectiveness of these approaches is the amphiphilic nature and low use-levels of the polymer. Pre-dispersing and slowly incorporating it into the system enables the
polymer to disperse and partition more successfully at interfacial regions of the formulation, reducing contact potential with
anionic elements of the formulation. The cationic and amphiphilic nature of the polymer has also been shown to provide
other benefits, including substantivity to the skin that enables
deposition of ingredients across a broad spectrum of water solubility and pH, a light and silky feel that is more appropriate for
skin care, and a natural-feeling barrier that provides resistance
to water and rub-off.
Cationic polymers can be successfully incorporated into skin
care systems employing anionic ingredients. Although approaches for using combinations of such ingredients vary and
can be material-specific, recently launched materials such as
the polymer Deposilk Q1 illustrate that utilizing and benefiting
from this class of materials in skin care can be straightforward.
Among the benefits that formulators can enjoy from the new
polymer are skin conditioning, a desirable sensory profile, water
resistant barrier protection, efficacy within high water and alcohol systems, and long lasting active ingredient deposition. Such
capabilities could provide new, unique products with excellent
cost-performance propositions to address emerging markets of
skin care consumers.
Reference list and additional information can
be found on the Internet – see Internet button
Mussarat Noor, Senior Formulating Chemist,
Air Products and Chemicals, Allentown, USA
COSSMA 12 I 2011