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Next-GeNeratioN Carbomer For aHa and bHa SyStemS

Lubrizol Advanced Materials researchers have developed Carbopol Ultrez 30 polymer, a new carbomer for low pH skin care systems

In the personal care market, cosmetic products must address the continuous desire of consumers for a beauty product that delivers multifunctional benefits in the shortest amount of

time. This is especially true in facial and neck care. According to Mintel, this market segment accounted for 81% of all global skin care product launches in 2012.1

Consumer demand for products that provide anti-aging and healthy skin benefits is a driving force for creating new cosmetics. With this knowledge, the formulator is confronted with the task of developing products in various forms that must address the many needs of consumers. Claims such as moisturization, anti-wrinkle, even skin tone, lightening or removal of dark spots, exfoliation and smoothing of the skin are made possible by the incorporation of active ingredients into these personal care formulas. Many of to-day’s key active ingredients are most effective at lower pH ranges, which mean that they are acidic or electrolytic in nature. In order to achieve the maximum level of benefits, a formulation must have the appropriate levels of such actives and thus must be formulated at pH below 5.0. Creating a beauty product with effective levels of acidic active ingredients, pleasant sensory attributes, satisfying rheological properties and stability is a challenge.

Low pH ViscosityThe pH of a personal care product, such as an emulsion or a gel, influences product performance. The pH of a system can determine the efficacy of actives and also the behavior of a rheology modifier. Traditionally, low pH systems uti-lized nonionic polymers, naturally-sourced gums such as cellulose and xanthan, clays, starches, and other anionic and cationic materials. While these materials have been around for ages, there is still a need for a rheology modi-fier that delivers the electrolyte efficiency, sensory aspects, added stability and overall efficiency to formulations at low pH. Traditionally, formulating at low pH using acrylic acid based polymers required using higher amounts of these polymer solids or adding a synthetic or natural co-thickener. In cases where a polymer is hydrophobically

modified, using higher polymer solids (>1.0 wt%) can have a negative impact on the sensory aspects, aesthetics and even sta-bility of the system. The second option is also not ideal, as natural co-thickeners like xanthan gum at high use levels are known for providing undesirable texture and unpleasant sensory character-istics to formulations. Carbopol Ultrez 30 polymer from Lubrizol Advanced Materials, Inc. has been developed to respond to the challenges of low pH formulating. This new carbomer is a crosslinked ho-mopolymer of acrylic acid useable over a broad pH range and has improved electrolyte efficiency and different sensory proper-ties than traditional polymers of similar composition. Carbopol Ultrez 30 polymer has been designed for improved efficiency in low pH applications, enabling the development of formulations where current acrylate-based technology falls short. To further highlight the efficiency ofCarbopol Ultrez 30 poly-mer, the viscosity was evaluated at 0.5wt% polymer use levels as a function of pH from 3.5 to 5.0. Measurements were made with a Brookfield RVT or DV-II at 20rpm and at 25°C. Figure 1 shows that Carbopol Ultrez 30 begins building viscosity after pH 3.5 and reaches a plateau around pH 4.0. By offering maximum and consistent viscosity above pH 4.0, this next-generation carbomer gives formulators more control over processing in production and facilitating viscosity adjustments.

Cary Sims, Bryan Moran and Marie Ollagnier • Lubrizol Advanced Materials, Inc. and Lubrizol Advanced Materials France SA

Fig. 1: Low pH Viscosity Response at 0.5% poLymeR Use

LeVeLs witH caRbopoL ULtRez 30 poLymeR

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Next GeNeratioN CarboMer

Alpha/Beta Hydroxy AcidsMany of today’s active ingredients vary in function and pH de-pendence. Two groups of actives, well established in the industry as delivering many skin benefits are α-hydroxy acids (AHAs) and β-hydroxy acids (BHAs). Both are used in personal care for skin rejuvenation, exfoliation, clarification and purification.

AHAs are a class of chemical compounds that occur naturally in fruits. One of the most widely used AHAs in personal care is gly-colic acid. It works primarily on the surface of the skin by removing dead surface layers, revealing smoother, softer and more even skin appearance.

At-home products will use less glycolic acid than those used at salons, doctors’ offices or by other trained individuals that can correctly apply and monitor the use of these products. The degree of activity is dependent on the use level of glycolic acid and the pH (acidity) of the final product. As it is the acid form of the active that is the most effective, the closer the pH of the formula is to the pKa of the acid, the greater the efficacy of the active.

Salicylic acid, a BHA, is an FDA-regulated, anti-acne active ingredient with a use level range of 0.5 to 2.0 wt% in the US. Being oil-soluble, this material has the ability to penetrate deeper into the layers of the skin versus water-soluble AHAs. The pH for BHA compounds must also be low for maximum efficacy.

AHAs in Gel SystemsPersonal care products containing AHA come in various product forms. Gel systems are the simplest and fastest way to deliver ac-tive ingredients to the skin for treatment. These systems usually include glycerin or other humectants for moisturization, rheology modifier(s), and active ingredients such as botanical extracts, skin conditioning ingredients and/or anti-irritancy agents. Figure 2 shows the simple gel-based systems that were evaluated with Carbopol Ultrez 30 polymer versus other acry-late-based benchmarks. Viscosity was determined for gels made with 1.0 wt% polymer and 1.0 wt% glycolic acid at pH 4.5 with a Brookfield viscometer at 20 rpm and at 25°C.

In Figure 2, combinations of Carbopol Ultrez 30 polymer and

xanthan gum were also evaluated at pH 4.5 with 1.0 wt% poly-mer and 0.25% xanthan gum in the presence of 1.0 wt% glycolic acid. Results show that Carbopol Ultrez 30 polymer gives the highest viscosity performance in these formulating conditions and in the presence of glycolic acid. Results also indicate that the addition of a co-thickener such as xanthan gum can enhance the viscosity of the system without negatively impacting the texture of the formula.

Low pH AHA O/W EmulsionsUnlike gels, O/W emulsions enable the formulator to design more sophisticated formulations with enhanced sensory char-acteristics, and give the opportunity to include a wider range of lipophilic actives.

It is well known that a rheology modifier is essential in order to offer appropriate texture and flow as well as to stabilize an emulsion. Even when emulsifiers and other structurants are used, they are often not enough to sufficiently stabilize a system. Formulating in a more challenging environment such as low pH further emphasizes the need to have an efficient rheology modifier that can balance the sensory attributes, stability and aesthetics of an emulsion.

Carbopol Ultrez 30 polymer was evaluated in a low pH emulsion at 1.0 wt% use level containing 1.0 wt% glycolic acid. Emulsions were developed at pH 4.5 and 4.0 (Table 1). A second test sample at pH 4.0 also contained 0.25% xan-than gum to study the enhanced viscosity efficiency due to the synergy between the gum and the polymer.

FIG. 2: PerFormance oF 1.0 wt% Polymer In Gel wIth 1 wt%

GlycolIc acId at Ph 4.5, wIth and wIthout xanthan Gum.

Nothing contained herein is to be considered as permission, recommendation, nor as an

inducement to practice any patented invention without the permission of the patent owner

table 1: aha oIl-In-water emulsIon

system wIth 1.0 wt% GlycolIc acId

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BHA EmulsionTo further demonstrate the performance of Carbopol Ultrez 30 polymer in low pH applications, a BHA emulsion was prepared with 2.0 wt% active salicylic acid at pH 4.0 (Table 2). This emulsion uses a light, branched ester, neopentyl glycol diethylhexanoate for a silky, non-greasy emolliency. PEG-20 methyl glu-cose sesquistearate and methyl glucose sesquistearate are two vegetable-derived emulsifiers providing stabilization along with cetearyl alcohol. Japanese green tea extract is added for its anti-inflammatory benefits in order to help reduce the poten-tial irritation of salicylic acid.

ConclusionFormulating at low pH offers some great advantages to enhance the performance efficacy of active ingredients, but it also provides some challenges. The aim of for-mulators is to create stable formulas that will deliver the various benefits consum-ers desire in a pleasant form, enabling a sensory experience that through its ease of use will encourage product loyalty and repeated use.

The Carbopol Ultrez 30 polymer has shown to be an efficient polymer at low pH, providing better viscosity, suspension, and stability in gels or emulsions containing challenging actives such as AHAs or BHAs. By improving the performance properties of traditional carbomers, the next-gener-ation carbomer meets the demands of an ever-changing personal care landscape. •

More info:To further assist formulators in using and

evaluating the presented technologies, additional information can be found at

www.lubrizol.com/personalcare

References 1.Mintel Executive Summary. “Category Insight:

Facial Care.” September 2012.

Fig. 3: PerFormance oF 1.0 wt% carboPol ultrez 30 Polymer in emulsion

with 1.0 wt% glycolic acid at Ph 4.5, with and without xanthan gum at Ph 4.0.

Nothing contained herein is to be considered as permission, recommendation, nor as an inducement

to practice any patented invention without the permission of the patent owner

table 2: bha emulsion system with 2.0 wt% salicylic acid