Whitepaper: Polyacrylate-1 Crosspolymer

Polyacrylate-1 Crosspolymer

The versatile cationic compatible rheology modifier for conditioning formulations

By Duane G. Krzysik, Senior Research and Development Associate; Xin Liu, Asia Pacific Technical Service Manager; Francine Shuster, R&D Manager; Krishnan Tamareselvy, Research Associate; Kevin Yoder, Marketing Manager, Carbopol Liquid Polymers

Noveon Consumer Specialties of Lubrizol Advanced Materials, Inc., a wholly owned subsidiary of The Lubrizol Corporation.

Formulators of personal care products are continually challenged to further differentiate their products in an effort to attract new consumers. This has led to more narrowly defined consumer market segments and to the development of specialized formulations to address more sophisticated consumer needs.

In many cases, high performance formulations are designed to deliver enhanced conditioning for hair or skin through the use of cationic ingredients and the delivery of conditioning additives. Traditionally, the available range of suitable rheology modifiers and deposition aids has been limited in these increasingly challenging formulations. Typical anionic thickeners may not be well suited in a low pH or cationic containing environment, and nonionic options may provide undesirable aesthetics.

Now, Polyacrylate-1 Crosspolymer overcomes these limitations and creates new formulating possibilities. This novel liquid rheology modifier was specially designed for use in low pH personal care applications where cationic compatibility and low to medium viscosity are desirable. This patent-pending new polymer offers high clarity, a smooth feel, shear-thinning rheology, and excellent suspension capabilities, all properties for which Carbomer polymers have long been the preferred choice in other applications.

The cationic compatible nature of this polymer enables formulators to take advantage of ingredients such as cationic conditioners or polymers which offer improved sensory and conditioning properties without sacrificing product aesthetics. This makes it ideal for use in conditioning shampoos and hair conditioners. Further, in surfactant-based applications with pH under 6.0, the polymer takes advantage of the unique Back-Alkaline formulation technique, making it possible for formulators to tailor rheology and pH to suit their specific needs.

The unique features of this exciting new polymer truly create new possibilities for today’s formulators by offering a liquid rheology modification solution that markedly expands the feasible formulation window versus that of more commonly used anionic rheology agents, such as Carbomer or Acrylates Copolymer.

Introduction

Formulations having pH < 6.0 and containing cationic components, such as cationic surfactants or polymers, are commonly referred to as “low pH” formulations. Cationic ingredients are commonly chosen for formulations used to treat or condition hair. There is an ongoing need and desire for better cationic compatible polymeric rheology modifiers for use in low pH formulations.

To meet this demand Polyacrylate-1 Crosspolymer was developed. This novel new polymer offers formulators cationic compatibility, smooth flow, shear thinning rheology, and suspension capabilities in applications below pH 6.0. It is surprisingly effective in thickening aqueous systems containing cationic conditioning ingredients (e.g., quaternary ammonium compounds and amines), cationic polymers, surfactants, and other similar ingredients. The unique design of this polymer features a carefully optimized balance of hydrophilic, hydrophobic, and semi-hydrophobic substituents, with amine functionality which further activates ionic (cationic) characteristics at low pH. Notably, the polymer incorporates a proprietary modified hydrophobe package which enables controlled associative thickening to help to build viscosity without sacrificing the desirable, smooth-flow rheology, clarity and suspension capability that is typical of Carbomer polymers.

Because of its cationic compatibility, functionality at low pH and desirable rheological properties, Polyacrylate-1 Crosspolymer offers formulators a whole new dimension in formulating hair conditioning products.

Novel Thickening Mechanism with Versatile “Back-Alkaline Technique”

Polyacrylate-1 Crosspolymer builds viscosity through the mechanisms of hydrodynamic thickening and controlled hydrophobic association when pH is reduced to less than 6.0 through the addition of an acid. This activates the ionic functionality of the polymer (Figure 1), causing the polymer to swell through charge repulsion (hydrodynamic volume expansion). Further, controlled hydrophobic association occurs by the unique combination of semi-hydrophobic and hydrophobic side chains at specific sites.

Acidic ingredients (such as lactic, glycolic, salicylic or fruit acids) used in personal care treatment products can serve both as active agents and acidifying agents for the polymer to achieve the desired viscosity.

Polyacrylate-1 Crosspolymer is further distinguished from many other rheology modifiers by its synergistic thickening with surfactants and salt, making it ideal for use in cleansing applications.
Figure 1 demonstrates the thickening mechanism in a surfactant-based system.

Acid (citric, lactic, glycolic or other acceptable acids) neutralization of Polyacrylate-1 Crosspolymer provides rheology control and clarity in surfactant containing formulations. It is recommended that this polymer be neutralized to a pH between 3.5 – 4.0 to obtain optimum viscosity and yield. The pH can then be adjusted by the addition of sodium hydroxide (or other bases) to the desired pH for a surfactant based system. The “Back-Alkaline Technique” is shown in Figure 2.

By using the “Back-Alkaline Technique”, the pH of the final product can be increased to as high as pH 7.0. This mechanism provides formulators with the versatility to tailor viscosity, clarity and yield value as desired and provides utility in a wider variety of formulations.

Polyacrylate-1 Crosspolymer in Conditioning / 2-in-1 Shampoos

The cationic-compatibility and low pH functionality of Polyacrylate-1 Crosspolymer enable the thickening of conditioning shampoo formulations and provide aesthetically pleasing smooth-textured flow while stabilizing shampoo formulations that rely on the suspension of conditioning ingredients.

In order to understand the effect of Polyacrylate-1 Crosspolymer on the conditioning properties of conditioning shampoo formulations, rheology and mechanical combing studies where conducted using a typical conditioning shampoo composition shown in Table 1. Polyacrylate-1 Crosspolymer at 0.75 wt% total solids was investigated in formulations that contained traditional cationic-conditioning polymers and two different particle size silicone emulsions (nonionic small particle size and anionic medium particle size emulsions). The combing studies were carried out using a strict washing procedure and utilized the Texture Analyzer to measure the force to comb through tresses. Untreated bleached tresses were washed with a 10 wt% total solids SLS solution, followed by baseline measurements of wet and dry combing force. The tresses were then shampooed with the test conditioning shampoo formulations, after which combing force measurements were again obtained to determine the change in combing force.

In the rheology portion of this study, Polyacrylate-1 Crosspolymer was found to have a synergistic thickening effect when formulated in combination with the cationic-conditioning polymers, providing an increase in both viscosity and yield (Figure 3). In the combing investigation, the polymer was found to work with cationic-conditioning polymers to improve the combing attributes of the conditioning shampoo formulations (Figure 4).

Further conditioning shampoo studies were performed where the compositions contained a 22 wt% total solids surfactant blend (ALS, SLES, Betaine) and 1 wt% total solids Polyacrylate-1 Crosspolymer. Here Polyacrylate-1 Crosspolymer was found to provide conditioning benefits similar to that of Polyquaternium-10, as measured by wet and dry combing on bleached hair. Even more significantly, it was also found that Polyacrylate-1 Crosspolymer provided superior stabilization and suspension of Dimethicone, as compared to the same formulation with Polyquaternium-10 and Dimethicone alone, which was unstable.

It must be noted that combing results are formulation dependent (especially true of conditioning / 2-in-1 shampoo formulations), where surfactant type, surfactant level, cationic-conditioning polymer type, conditioning polymer level and silicone type (size, viscosity, etc.) determine the overall performance of conditioning shampoos.

In summary, Polyacrylate-1 Crosspolymer can provide the following benefits in conditioning shampoo formulations:

•    Enhances viscosity and yield of surfactant based cleansers
•    Works with cationic conditioning polymers to improve combing performance (formulation
     dependent)
•    Enhances combing without use of cationic conditioners or silicones (formulation dependent)

Polyacrylate-1 Crosspolymer in Conditioner Formulations

The cationic-compatibility and low pH functionality of Polyacrylate-1 Crosspolymer make this polymer ideal for thickening conditioner formulations. The polymer can provide aesthetically pleasing smooth-textured flow while also stabilizing those formulations that rely on the suspension of insoluble conditioning ingredients.

In order to understand the benefits of Polyacrylate-1 Crosspolymer in rinse-off hair conditioners, a rheology study was conducted using a basic conditioner formulation which consisted of water, 1.4 wt% total solids Stearalkonium Chloride, 1.4 wt% total solids Cetearyl Alcohol, and neutralized to a pH of 3.8 to 4.2 using Citric Acid. Formulations tested included this basic formulation (base), base plus 1.4 wt% total solids Amodimethicone, base plus 0.3 wt% total solids Polyacrylate-1 Crosspolymer, and base plus 1.4 wt% total solids Amodimethicone and 0.3 wt% total solids Polyacrylate-1 Crosspolymer.

In previously conducted conditioner and emulsion formulation studies, Polyacrylate-1 Crosspolymer was found to synergistically improve rheology in combination with fatty alcohols and other fatty ingredients. In this particular conditioner study, the low level of Polyacrylate-1 Crosspolymer (0.3 wt% total solids) worked together with the Cetearyl Alcohol to provide a significant improvement in both viscosity and yield (Figure 5).

Based on these favorable rheology results, mechanical combing studies were then conducted to determine the effect of Polyacrylate-1 Crosspolymer on the conditioning properties of these rinse-off conditioners. The same combing test method described earlier for the conditioning shampoo studies was employed; however, in this case the test conditioner formulations were applied to the hair and thoroughly rinsed off one minute after application.

In the formulations tested, Polyacrylate-1 Crosspolymer was unexpectedly found to provide an outstanding improvement in wet and dry combing when used with Amodimethicone (Figure 6).

In summary, Polyacrylate-1 Crosspolymer provides the following benefits in conditioner formulations:

•    Enhances rheology and flow behavior by increasing viscosity and yield
•    Allows for the formulation of elegant emulsions exhibiting shear-thinning rheology through
     synergistic thickening with fatty alcohols and other fatty materials
•    Can improve the combing performance of hair conditioners (formulation dependent)

Formulating Guidelines

•    Recommended Use Level: 0.3 - 3.0 wt% solids (1.5 - 15.0 wt% as-supplied)
•    Recommended pH: < 6.0; optimal viscosity and clarity are achieved at pH 3.5 to pH 4.0 with the use
     of “Back-Alkaline Technique” to pH 4.0 to 6.0
•    Neutralization: Carboxylic acids (glycolic acid, lactic acid, citric acid, etc.)
•    Back-Alkaline Technique: Bases (sodium hydroxide, triethanolamine, etc.)
•    Surfactant Compatibility: Polyacrylate-1 Crosspolymer is compatible with anionic, nonionic,
     amphoteric and cationic surfactants.
•    Recommended Surfactant Active Use Levels: 8.0 – 22.0 wt% active (surfactant mixtures) or as
     needed for desired levels of foaming, viscosity, and clarity
•    Other Compatibility: Polyacrylate-1 Crosspolymer is compatible with cationic ingredients, silicones
     and most other ingredients, but is generally incompatible with high molecular weight anionic
     polymers.

Summary

Polyacrylate-1 Crosspolymer provides formulators with important new capabilities in a multi-functional rheology modifier: cationic compatibility, smooth flow, shear-thinning rheology, suspension capabilities and high clarity in low pH applications.

The novelty of this multi-purpose polymer suggests its use as a thickener / rheology modifier; as a stabilizer of emulsions with silicones, oils, emollients, and fatty alcohols; for suspending insoluble ingredients; and for enhancing the efficacy and deposition of active ingredients and cosmetic materials.

In hair conditioning formulations, Polyacrylate-1 Crosspolymer can be used to enhance the viscosity and yield of shampoo and conditioner formulations alone or synergistically with other ingredients including cationic conditioning polymers and fatty alcohols. Polyacrylate-1 Crosspolymer can provide stabilization and suspension of insoluble conditioning agents such as silicones. Depending upon the formulation and ingredients used, Polyacrylate-1 Crosspolymer can work with cationic conditioning polymers and silicones to improve the wet and dry combing properties of the formulation.

Because of Polyacrylate-1 Crosspolymer’s cationic compatibility, functionality at low pH, and desirable rheological properties, the polymer offers formulators a whole new dimension in formulating products that bring conditioning benefits to hair. The personal care formulator now has a much broader spectrum of easy-to-use liquid rheology modifiers from anionic polyacrylate alkali-swellable emulsion polymers, such as Acrylate Copolymers, to cationic polyacrylate acid-swellable emulsion polymers, i.e. Polyacrylate-1 Crosspolymer. The use of this unique material allows the cosmetic scientist to formulate high performance conditioning products with confidence.