J. Cosmet. Sci., 49, 335-342 (September/October 1998) Surfactant-free formulations employing a synergistic complex between a hydrophobically modified, cationic cellulose ether and amylose PETER N. KONISH and JAMES V. GRUBER, Amerchol Corporation, 136 Talmadge Road, Edison, NJ, 08818-4051. Accepted for publication August 31, 1998. Synopsis This paper describes the preliminary development of a non-traditional emulsifier system, with character- istics similar to a standard oil-in-water emulsion system, employing a unique polysaccharide/polysaccharide complex formed by non-covalent crosslinking of a hydrophobically modified, water-soluble cationic cellu- lose ether (Quatrisoft © Polymer LM-200, polyquaternium-24) with amylose, a component of normal potato starch. Six oil-in-water emulsions were prepared with different emollients or pigments, and their stability was monitored by lack of separation over a period of six weeks at room temperature. A prototype skin lotion was also prepared, and monitored for stability over a six-week time period at both room temperature and 45øC via a Brookfield viscometer. INTRODUCTION The most common, commercially useful emulsions are typically oil-in-water (1,2). The oily discontinuous phase in personal care applications is typically some type of emollient or conditioner, of which many are well known (3). For typical, unadulterated water, stable suspensions are generally impossible for any extended period of time. An emulsion formed from oil and water will usually coalesce quickly back to two layers unless the droplets of oil are very small, as occurs, for example, in microemulsions (4). Even in the case of microemulsions, the desire for the oil and water to separate will typically cause separation over time. In order for water to be useful as a continuous phase, its gross molecular structure must be altered so as to improve its ability to suspend the oily phase. Classically, the water structure is altered by addition of molecules that possess both hydrophilic (water-loving) and hydrophobic (water-avoiding) components, i.e., surfactants (5). Surfactants used in personal care products can also have profound physiological effects on the proteins and lipids that comprise human skin and hair (6-9). The body generally responds quickly to Peter N. Konish's present address is Mane USA, 60 Demarest Drive, Wayne, NJ 07470. 335

336 JOURNAL OF COSMETIC SCIENCE such assaults by replacing the lost oils and proteins (10). However, sometimes the body is not able to respond as expected and the normal healthy appearance of the skin becomes red and irritated (11-13). One response to this deficiency has been to employ polymeric thickhers that help to stabilize emulsions by imparting a yield point to the aqueous continuous phase. Two excellent examples of such polymers are the naturally occurring, marine-derived poly- saccharide, xanthan, and the synthetically derived, hydrophobically modified poly(acry- lates) (14,15). Both of these polymers can suspend oil droplets indefinitely when used at low concentration with or without additional surfactants. Both of these polymeric species, and in fact, most polymers that function in this capacity, are typically artionic polymers. They generally require the addition of base to promote their thickening and suspending characteristics. Because they are artionic in use, these polymers have little desire to interact with the proteins of the skin and hair. Cationic polymers, on the other hand, are very well known for their unique conditioning benefits because these polymers do have a natural attraction for the skin and hair (16-18). However, there are very few cationic polymers that can also be used to impart a yield point to the aqueous continuous phase of an emulsion. Some cationic polymers are capable of thickening aqueous mixtures, but they are not necessarily efficient rhe- ology modifiers and they are rarely used as conditioning polymers (19,20). On the other hand, some unique, hydrophobically modified cationic conditioning polymers, while showing some thickening abilities, do not impart a yield point to aqueous solutions. In particular, polyquaternium-24 has demonstrable hair and skin conditioning benefits but does not impart a yield point to aqueous solutions (21). Recently, we reported a unique, synergistic polysaccharide/polysaccharide blend wherein polyquarternium-24, when carefully blended with amylose, a linear, naturally occurring polysaccharide available from normal potato starch, affords an unusually thickened, aqueous, three-dimensional polymer network complex (22). This network creates a yield point in aqueous solutions when the polyquaternium-24 and amylose are used at low concentrations in very specific weight ratios. We wish to expand on the properties of this unique polymer blend by demonstrating that by employing the polyquaternium-24/ amylose complex, stable surfactant-free formulations can be developed. The aqueous complex can suspend a variety of oils and finely ground solid materials such as titanium dioxide. The combined use of the cationic conditioning polymer to also stabilize sur- factant-free emulsions shows that this hydrophobically modified cationic polymer is quite versatile. EXPERIMENTAL MATERIALS The preparation of the complex formed between polyquaternium-24 and amylose is described elsewhere (22). In summary, a hot aqueous solution of polyquaternium-24 is carefully blended with a hot aqueous solution of potato amylose, such that the resultant mixture is composed of 1.0 part polyquaternium-24, 0.25 part amylose, and 98.75 parts deionized water. The hot mixture is then carefully cooled, which allows the polymer complex to form, building aqueous viscosity. Additional raw materials used in the study