Formulating with Silicones and Natural Lipids

Formulating with Silicones and Natural Lipids Anne-Lise Girboux Dow Corning Europe Seneffe, Belgium Michael Starch Dow Corning Corporation Midland, Michigan USA

This article first appeared in the December 2005 issue of Happi. Natural lipids have played a role in personal care applications for thousands of years. Olive oil was used in Roman times for skin and hair care and is likely one of the first widely used emollients. In many modern personal care formulations, natural lipids have been replaced by synthetic esters and oils derived from petroleum. However, with growing consumer interest in natural ingredients, new opportunities exist for incorporating natural lipids in a variety of product forms. Silicones are a class of synthetic emollients used for over 50 years in personal care applications. Their distinctive aesthetic properties have led to applications in almost all categories of personal care products. When combined in formulations, the complementary properties of natural lipids and silicones can offer a range of functional and sensory benefits. Chemistry of Natural Lipids and Silicones Natural lipids are oily substances derived from plant or animal sources. These materials encompass a variety of chemical compositions, but most lipids used in personal care applications are mixtures of plant lipids in which the main components are triglycerides. The non-triglyceride components of triglyceride-rich plant lipids are referred to as the unsaponifiable fraction, which typically consists of tocopherols, sterols, free fatty alcohols and triterpenes. The natural lipids we discuss here are the triglyceride-rich fraction mechanically extracted from the seeds of various plants. Triglycerides are esters composed of one glycerin molecule bonded to three fatty acids, long-chain carboxylic acids in which the alkyl chain normally contains ten or more carbons. The three fatty acids can have the same or different chain lengths, and their carbon chains can be saturated or unsaturated. The fatty acid composition of triglycerides varies according to the source of the triglyceride. For example, the triglycerides derived from coconuts are rich in lauric acid (saturated C12 fatty acid), and in many cases, materials such as sodium lauryl sulfate still retain a slight odor of coconut oil, from which this surfactant is often made. Triglycerides can be classified according to their melting points, a consequence of the types of fatty acids present. Natural triglyceride oils are liquids at room temperature, while natural butters are soft solids. Mango butter is obtained from the seeds of the plant Mangifera indica, and it is a solid because stearic acid is the dominant fatty acid. In contrast, the triglycerides obtained from the seeds of the evening primrose (Oenothera biennis) are rich in polyunsaturated fatty acids such as linoleic acid, which have low melting points, and this lipid is an oil. Under the INCI nomenclature system, natural lipids are named according to the genus and species of the plant. If the plant has a common name, it is included in the INCI name. Thus, the INCI name for mango butter is Mangifera indica (mango) butter and for evening primrose oil, Oenothera biennis (evening primrose) oil. Triglycerides that are blends obtained from multiple plant sources are simply called vegetable oil. Silicones are synthetic polymers made from quartz (a natural form of crystalline silicon dioxide) and methanol. Most of the silicones used in personal care applications are based on polydimethylsiloxane, which is known by the INCI name dimethicone. Dimethicone is a linear polymer available in a range of molecular weights, and the molecular weight for a particular dimethicone determines its viscosity. Low molecular weight dimethicones (short polymers) have low viscosities, and viscosity increases with increasing molecular weight. Volatile silicones such as cyclopentasiloxane are shortchain cyclic polydimethylsiloxanes. 2 Another commonly used silicone is phenyl trimethicone, which is a highly branched phenyl-functional silicone. Benefits of Silicones and Natural Lipids In many ways, silicones and natural lipids provide complementary benefits in finished formulations. Silicones have excellent aesthetic properties and offer improved spreading, gloss and reduced stickiness. Volatile silicones (e.g., cyclopentasiloxane) provide transient emolliency because of their volatility and are good vehicles for pigments, sunscreens and antiperspirant salts. Natural lipids provide emollient properties and are generally better moisturizers than silicones, in part because they are more occlusive. Natural lipids that contain certain fatty acids can contribute to skin health in ways that silicones cannot. Polyunsaturated fatty acids such as linoleic acid (C18:2) and linolenic acid (C18:3) are called essential fatty acids (EFAs) because they are required for good health. They cannot be synthesized by the human body. In particular, two EFAs are receiving attention as nutritional supplements: α-linolenic acid (also known as omega-3 fatty acid or C18:3, n-3) and γ-linolenic acid (also known as omega-6 fatty acid or C18:3, n-6). Many plant-derived triglyceride oils are good sources of these fatty acids. Among their many functions in the body, EFAs are required for the lipids that are part of the skin s barrier function. It has been shown that topical application of borage oil, which is a good source of γ-linolenic acid, can help restore the barrier function of skin damaged by surfactants (1). Finally, natural lipids satisfy consumer demand that is driving the trend for more natural ingredients in personal care products. Silicones and natural lipids include materials with a wide range of aesthetic properties. Dimethicone is the most commonly used nonvolatile silicone emollient. The aesthetic properties of this polymer vary as a function of molecular weight. Low viscosity (low

molecular weight) dimethicone has a very light, dry, skin feel and excellent spreading properties. As the molecular weight of dimethicone increases, the skin feel becomes heavier and spreading more difficult. For this reason, high molecular weight dimethicones are often blended with a volatile silicone such as cyclopentasiloxane to help deliver a thin film on the hair or skin. Natural triglycerides from different sources vary in their fatty acid composition. This factor determines not only melting point (oil versus butter) but also aesthetics. Natural oils rich in polyunsaturated fatty acids have a light skin feel, while natural butters have a heavier feel. By blending natural lipids from different sources, it is possible to obtain natural lipids that give a skin feel similar to the feel from hydrocarbon emollients such as mineral oil or petrolatum. The two simple lotion formulations in Table 1 illustrate the complementary aesthetics of silicone and a natural lipid. An experienced sensory panel of 18 participants applied the two lotions and assigned scores for a number of common sensory attributes. The lotions were evaluated during rub-in and after panelists perceived the lotion had been absorbed. a Lotions A and B had similar skin feel during rub-in, but panelists found Lotion A to be less tacky. After the lotions were absorbed, there were several significant differences. Panelists found Lotion A to be less greasy, less tacky, have more slip, and to impart a smoother skin feel. Formulating Techniques Natural triglyceride lipids are much more polar than common silicones such as dimethicone and cyclopentasiloxane. This means that often silicones and natural lipids will not be miscible (mutually soluble). When silicones and natural lipids are used together in an emulsion formulation (as in the previous example), the immiscibility of the two kinds of ingredients is less of an issue than in other types of a The degree of absorption was based on panelists perceptions, not biological skin absorption. Table 1. Prototype Test Lotions Lotion A Lotion B Wt% Wt% Shea Butter 5.0 10.0 Dimethicone (100 cst) 5.0 --- Thickener/Emulsifier (Polyacrylamide and 2.0 2.0 C13-14 Isoparaffin and Laureth-7) Water q.s. to 100 q.s. to 100 formulations such as clear formulations or anhydrous sticks. As long as the emulsification system is flexible enough to accommodate both types of emollients, it does not matter that the silicone and natural lipid are not soluble in each other. In fact, the lack of mutual solubility may enhance the aesthetic effects of each emollient. In a production environment, when the oil phase components of a formulation are not miscible, it is generally a good idea to maintain some form of agitation in the oil phase blend tank so the various oil phase components are uniformly added to the batch. In formulations where the miscibility of the emollients is important, it is useful to know which silicones are 3 soluble in different natural lipids. We have found that natural oils generally have better solubility in silicones than do natural butters. And, some silicones are more miscible with natural lipids than others. Table 2 provides a general guide for the miscibility of common silicones in natural lipids. Clear anhydrous oils are examples of formulations that require complete miscibility of all ingredients. Table 3 shows an example of a clear sunscreen oil that depends on the miscibility of cyclopentasiloxane with the natural oil (a blend of vegetable oils) and three organic sunscreens. To make the simple sunscreen oil, mix all the ingredients at room temperature. Table 2. Miscibility of Natural Lipids with Common Silicones Common Silicone Natural Lipids Mango Butter Kokum Butter Shea Butter Natural Oils Cyclopentasiloxane M NM M M+ Dimethicone (350 cst) NM M NM M Phenyl trimethicone M+ NM M M+ M+ = Miscible at all ratios M = Miscible at some ratios NM = Not miscible Table 3. Dry-Feel Sunscreen Spray Vegetable oil (Cosmassage R-3, ICSC) 15.0 Cyclopentasiloxane (XIAMETER PMX-0245 Cyclopentasiloxane) 62.5 Ethylhexyl methoxycinnamate (octinoxate) 7.5 (Parsol MCX, DSM Nutritional Products) Octocrylene (Parsol 340, DSM Nutritional Products) 10.0 Ethylhexyl salicylate (octisalate) 5.0 (Escalol 587, International Specialty Products)

Table 4. Massage Oil Base Table 4 shows another clear anhydrous oil formulation. This product is intended for use as a massage oil and is based on the same vegetable oil blend as the clear sunscreen oil. In both cases, the vegetable oil blend was made by selecting a combination of natural oils from different plant sources to provide a light feel and rapid absorption. The aesthetics of this formulation can be modified by adjusting the ratio between the volatile silicone (cyclopentasiloxane) and the nonvolatile emollients. This massage oil is made by blending the ingredients in any order. Anhydrous sticks are another formulation type where miscibility between natural lipids and silicones is important. Sticks are based on a mixture of emollients and waxes and are made by heating the ingredients until the waxes melt, then pouring the molten formulation into a suitable mold for hardening. A good stick formulation is based on ingredients that are miscible in the molten and solid states. If the ingredients do not have sufficient miscibility after the formulation has solidified, the stick exhibits syneresis (oil bleed) over time as the immiscible components come to the surface. Table 5 shows a high SPF sunscreen stick formulation that contains two waxes, cetearyl alcohol and C30-45 alkyl methicone (and) C30-45 olefin, a silicone wax that increases the hardness of the stick. To make this stick, combine all the ingredients except the cyclopentasiloxane and heat to 75-80 C. Continue to mix and heat until the waxes and benzophenone-3 are completely melted and dissolved. Once the mixture is clear, begin cooling the Table 5. High SPF Sunscreen Stick 4 Cetearyl alcohol (Lanette O, Cognis Corporation) 20.00 C30-45 alkyl methicone (and) C30-45 olefin 3.00 (Dow Corning AMS-C30 Wax) Mangifera indica (mango) seed butter 20.00 Vegetable oil (Cosmassage R-3, ICSC) 3.50 Ethylhexyl salicylate (octisalate) 5.00 (Escalol 587, International Specialty Products) Ethylhexyl methoxycinnamate (octinoxate) 7.50 (Parsol MCX, DSM Nutritional Products) Homosalate (Neo Heliopan HMS, Symrise) 7.00 Octocrylene (Parsol 340, DSM Nutritional Products) 8.00 Benzophenone-3 (oxybenzone) 6.00 (Escalol 567, International Specialty Products) Cyclopentasiloxane (XIAMETER PMX-0245 Cyclopentasiloxane) 20.00 Table 6. Hair Pomade Vegetable oil (Cosmassage R-3, ICSC) 60.0 Isopropyl myristate (Crodamol IPM, Croda) 12.0 Caprylic/capric triglyceride (Myritol 312, Cognis Corporation) 13.0 Cyclopentasiloxane (XIAMETER PMX-0245 Cyclopentasiloxane) 15.0 formulation. Add the cyclopentasiloxane when the temperature has reached 50-60 C to minimize loss of the volatile silicone. After the silicone is added and blended, pour the formulation into molds and cool to room temperature. An anhydrous hair dressing (pomade) is similar to the formulation for a stick. Formulations of this type are softer than sticks because they are intended to be picked up with the fingers and applied to the hair. Pomades Vegetable oil (Cosmodan 20, ICSC) typically contain large amounts of lanolin and petroleum-derived emollients such as petrolatum and mineral oil. Table 6 shows a pomade based on shea butter and a vegetable oil blend with aesthetic properties similar to those of mineral oil. Phenyl trimethicone is included because it is miscible with both shea butter and the natural oils and provides gloss on the hair. As in the sunscreen stick, the C30-45 alkyl methicone (and) C30-45 olefin provides the proper consistency in the formulation. The pomade is made by combining all the ingredients and heating at 75-80 C while mixing until a clear mixture is obtained. Table 7 illustrates a facial moisturizer that contains a mixture of silicone, natural lipid and ester emollients. It also contains a UVB sunscreen (octinoxate) and a UVA sunscreen (avobenzone). To prepare the formulation, combine Butyrospermum parkii (shea butter) 42.5 Phenyl trimethicone (Dow Corning 556 Cosmetic Fluid) 10.0 C30-45 alkyl methicone (and) C30-45 olefin 5.0 (Dow Corning AMS-C30 Wax)

Table 7. Facial Moisturizer with SPF Phase A Ethylhexyl methoxycinnamate (octinoxate) 3.0 (Parsol MCX, DSM Nutritional Products) Butyl methoxydibenzoylmethane (avobenzone) 1.5 (Parsol 1789, DSM Nutritional Products) Glyceryl stearate (and) PEG 100 stearate (Arlacel 165, Uniqema) 4.0 Butyrospermum parkii (shea butter) 1.0 Stearyl dimethicone (Dow Corning 2503 Cosmetic Wax) 3.0 Cetyl alcohol 1.0 Camelina sativa seed oil (Camelina Oil, ICSC) 4.0 Isononyl isononanoate (Dub ININ, Stearinerie Dubois Fils) 3.0 Cyclopentasiloxane (XIAMETER PMX-0245 Cyclopentasiloxane) 8.0 Phenoxyethanol (and) methylparaben (and) ethylparaben (and) 0.5 propylparaben (and) butylparaben) (Sepicide TM HB, Seppic SA) Cyclopentasiloxane (and) dimethicone crosspolymer 5.0 (Dow Corning 9040 Silicone Elastomer Blend) Phase B Glycerin 2.0 Water 60.0 Phase C Polyacrylamide (and) C13-14 isoparaffin (and) laureth-7 4.0 (Sepigel TM 305, Seppic SA) Table 8. Hand and Body Moisturizing Cream Phase A Water 74.8 Cetyl alcohol (Lanette 16, Cognis) 4.0 Mangifera indica (mango) seed butter 2.0 Garcinia indica seed butter (Cosmosil-K, ICSC) 4.0 Butyrospermum parkii (shea) butter 4.0 Dimethicone (XIAMETER PMX-200 Silicone Fluid, 350 cst) 2.0 Phase B Sodium polyacrylate (and) dimethicone (and) cyclopentasiloxane 4.0 (and) trideceth-6 (and) PEG/PPG-18/18 dimethicone (Dow Corning RM 2051 Thickening Agent) Phase C Glycerin 5.0 DMDM hydantoin (Glydant, Lonza Inc.) 0.2 the first two ingredients for Phase A and heat them to 60 C. Be certain the avobenzone is dissolved, then add the next four Phase A ingredients, making sure each has melted before adding the next. Add the rest of the Phase A ingredients and mix until uniform. Next, combine the ingredients for Phase B and mix into Phase A with rapid stirring. Cool the formulation to room temperature while continuing to mix, then add Phase C. The addition of Phase C will thicken the formulation significantly, so the mixer speed must be increased to maintain good agitation. Mix until the formulation is smooth and uniform in appearance. Table 8 shows another moisturizer based on the combination of natural butters and silicone. This formulation includes three natural butters and uses a silicone-based thickener and emulsifier. To prepare it, heat the water to about 60 C and mix in the rest of the ingredients for Phase A. The addition order is not critical, but it is important to make sure the cetyl alcohol and the butters are melted before adding the dimethicone. Begin cooling the batch and add Phase B. As Phase B is added the formulation will thicken, so the mixer speed must be increased to maintain good agitation. When the batch has cooled to below 45 C, add the Phase C ingredients and mix until uniform. Summary Natural lipids and silicones offer a variety of benefits and formulation possibilities, and they provide complementary properties in skin and hair care formulations. In some formulations, the mutual solubility of silicones and natural lipids is important, and we have presented guidelines for preparing clear oil and stick formulations. In emulsion systems, the miscibility of silicones and natural lipids is less important, providing the emulsifiers used in the formulation can accommodate both types of ingredients. 5

References 1. Nissen, HP, Biltz, H and Mugli, R, Borage Oil, Cosmetics & Toiletries, 110:71-76 (1995) LIMITED WARRANTY INFORMATION PLEASE READ CAREFULLY The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer s tests to ensure that our products are safe, effective and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent. Dow Corning s sole warranty is that our products will meet the sales specifications in effect at the time of shipment. Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted. DOW CORNING SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY. DOW CORNING DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES. Dow Corning is a registered trademark of Dow Corning Corporation. We help you invent the future is a trademark of Dow Corning Corporation. XIAMETER is a registered trademark of Dow Corning Corporation. All other trademarks are property of their respective owners. 2008, 2009 Dow Corning Corporation. All rights reserved. Printed in USA AGP10182 Form No. 27-1219A-01