Formulating for Electrolyte Resistance in Conjunction with Sensory Appeal

Dec 1, 2012 | Contact Author | By: Marie Ollagnier; Gordon Hsu, PhD; Bryan Moran; and Laure Buquen; Lubrizol Advanced Materials
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Title: Formulating for Electrolyte Resistance in Conjunction with Sensory Appeal
electrolytesx inverse emulsion polymerx rheologyx stabilityx sensoryx
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Keywords: electrolytes | inverse emulsion polymer | rheology | stability | sensory

Abstract: Skin care formulations often are enriched with high levels of electrolytic ingredients for various skin benefits. However, these have a negative impact on the viscosity, texture and stability of a system. Described in this article is a multifunctional polymer that is designed to provide excellent electrolyte resistance along with a pleasant sensory profile, as will be shown.

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M Ollagnier, G Hsu, B Moran and L Buquen, Formulating for electrolyte resistance in conjunction with sensory appeal, Cosm & Toil

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Repair, protection and moisturization are key consumer needs in skin care, and components that are used to deliver against these product claims are often electrolytic in nature. Common examples include mono- and multi-valent electrolytic salts of materials such as alpha hydroxy acids, pyrrolidone carboxylic acid (PCA) and phenylbenzimidazole sulfonic acid (PBSA). In addition to performance against product claims, though, overall consumer acceptance is heavily swayed by product aesthetics. Sensory performance is an important parameter that provides indulgence to the user and can convey the perception of efficacy. However, balancing rheology and stabilization properties with aesthetic properties in high actives-containing formulations is a common challenge faced by the formulator.

It is well-understood that electrolytic actives can suppress the viscosity of formulations thickened with ionic rheology modifiers, and while nonionic and even slightly anionic polymers such as polysaccharides are inherently more electrolyte-tolerant, they are intrinsically less efficient and known to exhibit unpleasant textures and undesirable sensory properties, such as stickiness. Therefore, in order to perform the required emulsification, co-emulsification, stabilization and rheology modification in oil-in-water emulsion systems but with improved electrolyte tolerance, a new polymera based on an anionic pre-neutralized acrylate copolymer was developed by inverse emulsification. Referred to hereafter as the IE-acrylate copolymer, its properties and capabilities were assessed, as described.

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This content is adapted from an article in GCI Magazine. The original version can be found here.

 

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Table 1. Effect of the addition of a co-emulsifier on a control emulsion

Table 1. Effect of the addition of a co-emulsifier on a control emulsion

Effect of the addition of a co-emulsifier on a control emulsion formulated with 10% of a cetyl ethylhexanoate and 1.0% w/w polymer solids at pH 5.5

Table 2. Test emulsions

Table 2. Test emulsions

Emulsion containing 2–4% w/w solids levels of PBSA, 10% of cetyl ethylhexanoate, 1% w/w polymer solids, with and without 0.2% w/w solids acrylates/C10–30 alkyl acrylate crosspolymer (pH 7)

Figure 1. Viscosity as function of % w/w polymer solids in aqueous dispersion at pH 6.5–7.5

Figure 1. Viscosity as function of % w/w polymer solids in aqueous dispersion at pH 6.5–7.5

Thickening is the primary function of rheology modifiers, which change the physical properties of a system and the migration rate of suspended components. Viscosity measurements, shown here, were made on an aqueous dispersion of the polymer, compared with other commercially available inverse emulsion polymers and thickeners selected for benchmarking purposes, at different concentrations of polymer solids.

Figure 2. pH curve at 1% w/w polymer solids

Figure 2. pH curve at 1% w/w polymer solids

The viscosity of 1% w/w polymer solids in the pH range of 5.5–11; the IE-acrylate copolymer provided excellent and consistent viscosity around 45,000 mPa•s above pH 6.5 but showed less thickening efficiency at pH 5.5-6.5.

Figure 3. Comparative electrolyte tolerance of different polymers with NaPCA

Figure 3. Comparative electrolyte tolerance of different polymers (1% w/w total solids) in aqueous dispersion in the presence of NaPCA at dispersion pH

The viscosity provided by 1% w/w polymer solids IE-acrylate copolymer was compared with other commercially available inverse emulsion polymers and thickeners in the presence of these selected electrolytes in an aqueous dispersion at the given pH. The IE-acrylate copolymer demonstrated superior thickening performance and worked as the sole emulsifier, emulsion stabilizer and thickener at pH ≥ 6.5.

Figure 4. Comparative electrolyte tolerance of different polymers with ZnPCA

Figure 4. Comparative electrolyte tolerance of different polymers with ZnPCA

The viscosity provided by 1% w/w polymer solids IE-acrylate copolymer was compared with other commercially available inverse emulsion polymers and thickeners in the presence of these selected electrolytes in an aqueous dispersion at the given pH. The IE-acrylate copolymer demonstrated superior thickening performance and worked as the sole emulsifier, emulsion stabilizer and thickener at pH ≥ 6.5.

Figure 5. Electrolyte tolerance in aqueous dispersion with acrylates/C10–30 alkyl acrylate crosspolymer

Figure 5. Electrolyte tolerance in aqueous dispersion with acrylates/C<sub>10–30</sub> alkyl acrylate crosspolymer

Water dispersion of 1% w/w solids IE-acrylate copolymer in combination with 0.2% w/w acrylates/C10–30 alkyl acrylate crosspolymer provided similar to better electrolyte resistance, compared to 1.2% w/w solids IE-acrylate copolymer, and better aesthetics compared to 1.2% w/w solids acrylates/C10–30 alkyl acrylate crosspolymer in this aqueous dispersion at pH 5.5.

Figure 6. Emulsification of different types of emollients at 5%, 10%, 20% and 0.4% w/w polymer solids at dispersion pH

Figure 6. Emulsification of different types of emollients at 5%, 10%, 20% and 0.4% w/w polymer solids at dispersion pH

The IE-acrylate copolymer was capable of emulsifying various types of emollients at a low concentration. Further, its ability to impart viscosity to the emulsion increased as the polarity of the oil phase increased.

Figure 7. Electrolyte resistance of 1% w/w polymer solid aqueous dispersion with different levels of SAP at dispersion pH

Figure 7. Electrolyte resistance of 1% w/w polymer solid aqueous dispersion with different levels of SAP at dispersion pH

The IE-acrylate copolymer showed better viscosity response than the other polymers in water dispersions containing high levels of the monovalent ascorbic acid salt.

Figure 8. Effect of PBSA on viscosity at 1% w/w polymer solids in aqueous dispersion (pH 7)

Figure 8. Effect of PBSA on viscosity at 1% w/w polymer solids in aqueous dispersion (pH 7)

The IE-acrylate copolymer provided the best viscosity in the presence of different levels of neutralized PBSA. Notably, most commercially available inverse emulsion polymers tested were unable to provide viscosity in the presence of just 1% w/w solids PBSA.

Footnotes [Ollagnier 127(12)]

a Novemer EC-2 Polymer (INCI: Sodium Acrylates/Beheneth-25 Methacrylate Crosspolymer (and) Hydrogenated Polydecene (and) Lauryl Glucoside) is a product of Lubrizol Advanced Materials, Inc.

b The Model DVII+ Viscometer is manufactured by Brookfield.

c Carbopol Ultrez 10 Polymer (INCI: Carbomer), and
d Carbopol Ultrez 20 Polymer (INCI: Acrylates/C10–30 Alkyl Acrylate Crossopolymer) are products of Lubrizol Advanced Materials, Inc.

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