Evaluating the Physiochemical Properties of Emollient Esters for Cosmetic Use

Dec 1, 2010 | Contact Author | By: Mihaela Gorcea and Donna Laura, International Specialty Products (ISP)
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Title: Evaluating the Physiochemical Properties of Emollient Esters for Cosmetic Use
sensoryx estersx spreadingx contact anglex surface tensionx viscosityx dielectric constantx refractive indexx
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Keywords: sensory | esters | spreading | contact angle | surface tension | viscosity | dielectric constant | refractive index

Abstract: This study assesses the physicochemical properties of four known cosmetic emollient esters in vitro to predict their sensorial benefits and correlate their properties with in vivo sensory attributes. This evaluation serves as a guide to selecting specific emollient esters for various cosmetic applications and to predicting their sensory attributes.

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M Gorcea and D Laura, Evaluating the physiochemical properties of emollient esters for cosmetic use

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Sensory properties in skin care formulations are produced mainly by emollients, rheology modifiers, emulsifiers and humectants. Emollient esters are cosmetic ingredients that help maintain skin’s softness and plasticity, form semi-occlusive films for moisturizing benefits, reduce the itching sensation often present in dry skin, and improve the appearance of the stratum corneum. As components of cosmetic formulations, emollient esters act mainly as moisturizers, plasticizers and tactile modifiers when applied to skin.

In skin care emulsions, emollients are generally used at levels between 3–20% w/w, representing the second major ingredient after water. This use level varies depending upon several parameters including the oil phase composition, level of emulsifier blend, compatibility between ingredients, desired after feel, and the type, use level and solubility of UV filter in the ester (for sunscreens). Therefore, emollients play a major role in influencing the skin feel of formulations.

Based on their chemical structures, emollients can be categorized as esters, hydrocarbons, glycerides, ethers, fatty alcohols and silicone derivatives. When formulating cosmetics, the product developer’s choice of emollient depends on several important factors such as chemical structure, polarity, molecular weight, spreading attributes, viscosity, solubility, contact angle and surface tension.

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Table 1. Viscosity and spreading of emollient esters

Table 1. Viscosity and spreading of emollient esters

Each emollient was measured in triplicate and repeated for a total of six measurements. The spreading values for all four molecules are shown here.

Table 2. Physicochemical properties of the four esters

Table 2. Physicochemical properties of the four esters

Surface tension values reported here represent an average of 20 trials. The measurements were conducted at 21–23°C and 24–35% RH.

Table 3. In vivo sensory evaluation of the four esters

Table 3. In vivo sensory evaluation of the four esters

The results obtained from the in vivo sensory evaluation are shown here.

Figure 1. Spreading vs. viscosity correlation

Figure 1. Spreading vs. viscosity correlation

The correlation between spreading values of the esters 10 min after application on the artificial membrane and their viscosities

Figure 2. Contact angle

Figure 2. Contact angle

Contact angle of a liquid droplet on a solid surface at the air-solid-liquid contact point

Figure 3. Contact angle of diisopropyl adipate

Figure 3. Contact angle of diisopropyl adipate

Contact angle of diisopropyl adipate, where a = θintial and b = θfinal

Figure 4. Contact angle of isodecyl neopentanoate

Figure 4. Contact angle of isodecyl neopentanoate

Contact angle of isodecyl neopentanoate, where a = θintial and b = θfinal

Figure 5. Contact angle of isocetyl stearate

Figure 5. Contact angle of isocetyl stearate

Contact angle of isocetyl stearate, where a = θintial and b = θfinal

Figure 6. Contact angle of octyldodecyl stearoyl stearate

Figure 6. Contact angle of octyldodecyl stearoyl stearate

Contact angle of octyldodecyl stearoyl stearate, where a = θintial and b = θfinal

Footnotes [Gorcea 125(12)]

a Ceraphyl 230 (INCI: Diisopropyl Adipate);
b Ceraphyl SLK (INCI: Isodecyl Neopentanoate);
c Ceraphyl 494 (INCI: Isocetyl Stearate); and
d Ceraphyl 847 (INCI: Octyldodecyl Stearoyl Stearate) are all products of ISP, Wayne, N.J. USA.

e Vitro-Skin is a substrate manufactured by IMS Inc., Portland, Maine, USA.

f Drop Shape Analyzer (DSA) 10 is a device manufactured by Krüss GmbH, Hamburg.

g The High-purity Silicone Rubber substrate used for this study is manufactured by McMaster-Carr, Elmhurst, Ill. USA.

h Brookfield RVDV-II + viscometer is a device manufactured by Brookfield Engineering Laboratories, Middleboro, Mass. USA

j The BI-870 dielectric constant meter is manufactured by Brookhaven Instruments, Holtsville, N.Y. USA.

k The Abbe NAR 3T Refractometer is manufactured by Atago, Japan.

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