NATURALS
CCT■ Cetyl alcohol■ Kester Wax K-48■ Kester Wax K-56■ Kester Wax K-59■
800 700 600 500 400 300 200 100 0
0 1 2 3 4 5 % Wax added to Base #1
Figure 4: Complex modulus changes with wax addition (Base 1, Formulas 1-11)
series of experiments1
Koster Keunen conducted a comprehensive to evaluate the impact
of adding them in increasing concentrations to different O/W emulsions. Three very different formula bases were designed based on previous formulation work. Base 1 is a leave-on chassis that can be used
in skin care formulations with a neutral emulsifier and the oil phase range of 13-16%. Base 2 is another leave-on skin care chassis using an anionic emulsifier and the oil phase is 25-31%. Base 3 is a chassis for any hair conditioner, the emulsifier is cationic and the oil phase is 16-22%. Tables 1-3 show their compositions and the
modifications made to them for testing. Each emulsion base was modified by adding five different ingredients at 3% and again at 6%, then observing the different results. The ingredients were our three waxes, along with two widely used oil phase components - caprylic/capric triglycerides (CCT) and cetyl alcohol - as controls. For each of the eleven modifications per base, we recorded the following properties: ■ Emulsion viscosity (cP): Measured at one week, with a Haake Mars rheometer at constant shear ■ Emulsion complex modulus (Pa): Measured at one week, with a Haake Mars rheometer at increasing oscillation stress values
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CCT■ Cetyl alcohol■ Kester Wax K-48■ Kester Wax K-56■ Kester Wax K-59■
40000 35000 30000 25000 20000 15000 10000 5000 0
0 1 2 3 4 5 % Wax added to Base #2
Figure 5: Complex modulus changes with wax addition (Base 2, Formulas 12-22)
■ Sensory emulsion properties: Evaluated with human panel testing, rated on a scale of 1=least to 5=most
Results The viscosity of Formulas 1-33 at one week are grouped by base and plotted on graphs, where the y-axis is viscosity (in cP) and the x-axis is the percentage wax added to each base. Figures 1, 2 and 3 correspond to Bases 1, 2 and 3 respectively. The complex modulus (G’) of Formulas
1-33 was also measured at one week. Results are grouped by base and plotted on graphs, where the y-axis is G’ (in Pa) and the x-axis is the percentage wax added to each base. Figures 4,5 and 6 correspond to Bases 1, 2 and 3 respectively. Formulas 1-22 were evaluated (via human panel, n=10) for sensory and performance parameters pertaining to skin care (Tables 5 & 6). Formulas 23-33 were evaluated on mannequin heads for sensory and performance parameters pertaining to hair care (Table 7). All formulas were evaluated, but only relevant results are shown (controls without wax, additions of 6% of each of our waxes).
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CCT■ Cetyl alcohol■ Kester Wax K-48■ Kester Wax K-56■ Kester Wax K-59■
7000 6000 5000 4000 3000 2000 1000 0
0 1 2 3 4 5 % Wax added to Base #3
Figure 6: Complex modulus changes with wax addition (Base 3, Formulas 23-33)
Each of the three wax esters reviewed
showed improvements in the overall appearance of the emulsions studied. Specifically, they can impact O/W emulsions by increasing opacity, gloss and overall brightness, making formulas look more expensive and luxurious. Each also creates differences beyond these first attributes. The study shows that both cetyl palmitate
and stearyl stearate have a pronounced effect on the visual and textural properties of an emulsion, without affecting the formula viscosity. Adding cetyl stearate to emulsions also improves the above visual and textural properties, with the added function of being a highly effective viscosity builder. Cetyl stearate is comparable in this sense to cetyl alcohol, a well-known emulsion viscosity builder. The waxes did not show any immediate impacts
on the formula performance, be it skin or hair care. From a functional standpoint, they are natural opacifiers, texture modifiers and viscosity modifiers. Future work includes more comprehensive sensory testing, gathering TEWL data, and increasing the number of alkyl esters studied.
Formulating anhydrous systems Cosmetic chemists who formulate anhydrous products, such as sticks, bars or balms, are
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www.personalcaremagazine.com
March 2022 PERSONAL CARE
Modulus G’ (Pa)
Modulus G’ (Pa)
Modulus G’ (Pa)
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