576 JOURNAL OF COSMETIC SCIENCE SOLVING MANUFACTURING PROBLEMS IN EMULSION PRODUCTS T. Joseph Lin, Ph.D. 628 Enchanted Way, Pacific Palisades, CA 90272 Introduction Cosmetic manufacturers today are faced with increasing global competition and the ability to produce a wide range of products at a consistently high level of quality is extremely important. To reduce costs, manufactmers have increased batch sizes, and manufacturing failures are more expensive than ever in terms of lost materials and failure to meet scheduled delivery dates. Toe pressures and time demands on cosmetic chemists have never been greater. Moreover, to cope with fast-changing market demands, cosmetic chemists are often required to remove or add certain ingredients into the existing formulations to improve product performance or enhance perceived consumer value. One danger is increased ingredients complexity and the possibility of unexpected chemical reactions or physical interactions which may affect product performance and shelf life. Too often, because of the intense pressures of competition, insufficient time is allotted for stability testing of the reformulated products, resulting in stability failure and expensive product recalls. Among the various types of cosmetic formulations, emulsion-based products continue to enjoy popularity because they look elegant, provide nice skin feel, and are very versatile in applications. Allowing easy incorporation of many water and oil-soluble ingredients, they can be adopted to formulate a wide range of O/W or W/O type skin-care, sun-care and hair-care products. In the past, cosmetic formulators have generally tended to stick to their favorite "tried-and-true" emulsification systems, using mostly well-known and familiar ingredients to formulate new products. However, intense market competition has change the rules and formulation chemists are often forced to use new ingredients without a well-established performance record or accurate information about their physical/chemical properties. Natural, Organic and "Chemical-Free" Emulsions For example, the popularity of "natural/organic" foods has stimulated the market for "organic" or "natural" cosmetics. Formulation chemists at cosmetic manufacturers are pressured to come up with all-natural or "chemical-free" cosmetics. Chemists working for raw material suppliers are also pressed to come up with effective "natural" or "chemical-free" surfactants, preservatives and other functional materials. Since there are no universally agreed upon definitions for words like "chemical," "natural," or "organic," depending of how the terms are defined, such products can be difficult or nearly impossible to create. Unlike well-defined pure chemicals such as methylparaben or imidazolidinyl urea, a substance advertised as a "natural" preservative may be a complex mixture of many naturally-derived and synthetic materials of unknown chemical composition. This means there is surely a greater chance of unexpected interactions with other ingredients in the formulation which may cause product degradation and instability. Emulsion Stability and the Second Law of Thermodynamics By their nature, emulsified products consist of two incompatible liquids, usually a water-soluble phase and an oil-soluble phase. They are thermodynamically unstable, meaning that they all have a limited shelf life, and phase separation will take place some time after manufacturing. A minimum of two-year stability is required for most commercial cosmetic emulsions. This requirement would not be difficult to meet if we had a quick and reliable method or instrument to predict the shelf life of a particular emulsion.

2007 ANNUAL SCIENTIFIC SEMINAR 577 Unfortunately, we still do not have such a tool available today. Standard accelerated stability tests used at present, including placing samples in varying environments, are useful but not completely reliable unless sufficient time is allowed for the tests. For practical purposes, sufficient time here can be several weeks to several months. In addition, the stability and physical properties of emulsion products are not only affected by the ingredients in the formulation, but also by process variables such as intensity of mixing, cooling rate, emulsification temperature. Carefully-planned process studies can be very important in assuring trouble-free manufacturing. Low-Energy Emulsification In the past, the cost of energy used in manufacturing cosmetics has not been an important economic issue. With energy costs expected to increase along with the continuing global warming trend, many large manufacturers of consumer products are already facing strong pressure to reduce their energy consumption. Although cosmetic manufacturing is not an energy-intensive industry, it can be expected that we will also be required to reduce energy usage. Shortly after the 1970 's oil crisis I published a series of papers in SCC Journal on an energy-saving method of processing cosmetic emulsions, called "Low-Energy Emulsification, LEE (1). In addition to reducing energy consumption, LEE offers the advantage of significantly reduced processing time. In some cases, it is possible to reduce both the energy consumption and emulsion processing time by as much as 50%. The principle of LEE is based on the fact that conventional processing of cosmetic emulsion uses far more energy than is theoretically required or practically needed. By using energy when needed and where needed, we can reduce its consumption significantly. In addition, by using less energy to start, we can also vastly reduce the process time required for removing the energy. In making cosmetic emulsions, often the most time-consuming step is cooling of the batch, which can take several hours for large batches. Cooling is, of course, removal or discarding of energy, which takes time. Reducing the need for cooling can not only reduce energy costs but also shorten production time. Proper application of LEE saves energy and increases production efficiency without compromising product quality (2). In fact, in some cases, emulsions with finer droplet size distribution can be made using LEE than can be with a conventional method (3). This means that sometimes less really can produce inore. Less Is More The LEE principle can be applied, besides in processing of emulsions, to reduce costs and enhance production efficiency or product performance in other areas. An example is the use of surfactants in formulating skin care products. While surfactants are indispensable in assuring emulsion stability, it does not follow that the use of more surfactants will always ensure more stability and better product performance. What is important here is not just the quantity, but also obtaining a good balance. Excessive amounts of certain surfactants can not only reduce stability and shelf life but can also contribute to higher irritation potential in some skin care products. Thus, the best strategy for stabilizing an emulsion may not be simply adding more surfactants, but could rather be a reduction of a certain surfactant in the formulation to obtain the correct hydrophile-lipophile balance (filB) and hence better stability and lowered irritation potential ( 4 ). References (1) T. J. Lin, "Low-Energy Emulsification-I Principles and Applications" J. Soc. Cosme!. Chem., 29, 117 (March, 1978) (2) T. J. Lin, T. Akabori, S. Tanaka and K. Shimura "Low-Energy Emulsification-II Evaluation of Emulsion Quality'' J. Soc. Cosme!. Chem., 29, 745 (Dec.,1978) (3) T. J. Lin, T. Akabori, S. Tanaka and K. Shimura "Low-Energy Emulsification V, Mechanism of Enhanced Emulsification" Cosmetics and Toiletries 98, 67 (Oct. 1983) (4) T. J. Lin, "Low-Surfactant Emulsification" JSoc. Cosmet. Chem., 30, 167 (May,1979)