Reference: Romanowski and Schueller, Beginning Cosmetic Chemstry, 2003

Transcription

1 CEM 470 Triglycerides: A Primary Ingredient for Making Surfactants Reference: Romanowski and Schueller, Beginning Cosmetic Chemstry, 2003 The possible number of materials useful in the formulation of personal-care products is staggering, with new products being introduced all the time. Understanding the source of many of the raw materials and the technology needed to modify them is important. ne needs to start by considering the most basic raw materials, or primary ingredients. The basic raw materials find their origins in natural oils, fat and waxes, and in petroleum feedstocks such as propylene and ethylene. This article will concentrate on natural oils, waxes and butters. Nature has provided a plethora of materials that are potentially useful in personal-care applications. Performance and cost are determined by the selection of oils and waxes, both as such and in surfactant molecules. ils, Fats, Waxes and Butters The terms oils, fats, waxes and butters have been misused over the years. The misuse of these terms is due to the fact that all of these terms that relate to physical properties. Wax is an ester of a fatty acid and a fatty alcohol. Triglycerides are a triester of glycerin. Triglycerides: Triglycerides are the tri-ester of glycerin with three equivalents of fatty acid. Fatty acids are defined as those acids having alkyl or alkylene groups that are C-5 and higher. Figure 1 shows the reaction that produces a triglyceride. Triglycerides are a very important clas of raw mateials for making fatty derivatives, including surfactants. Saponification is a general term to define the chemical reaction that breaks the ester linkage. When the triglyceride is saponified to make a surfactant, such as soap, glycerin is liberated. When a wax is saponified, a fatty alcohol is liberated. Thus, the type of products that can be made using the two types of materials are quite different functionally. Glycerin is water soluble, and the fatty alcohol is water insoluble. Differentiating among triglycerides: Because determining a melting range for these compounds can be uninformative (oils, fats and butters consist of many fractions of similar compounds), titer point is generally used instead of melting point. The titer is defined as the re-solidification point of the melted oil, fat, butter or wax. The procedure is to heat the product to be tested until it is completely liquid, then to slowly cool with stirring. This is done until the temperature stays

2 constant for 30 seconds, or begins to rise. The titer point is the highest temperature indicated by this rise. + 3 R fatty acid C()R C()R C()R + 2 glycerol Figure 1 triglyceride Fats have a titer point of greater than 40.5 C. ils have a titer point of less than 40.5 C. Butters have a titer between 20 C and 40.5 C. ils are liquids at room temperature. We now use this word to describe any compound that is a liquid and is insoluble in water. As a result, jojoba is referred to as an oil, despite the fact it is really a liquid wax. It is therefore very important to realize that the terms wax and triglyceride define the chemical nature of a compound; the terms oil, butter and fat define a physical property. Classification: The CTFA now requires the genus species of the plants or insects that produce a given wax, oil, butter or fat and all products that are derived from the various oils, fats, butters and waxes. This is due, in part, to the European Union s use of the Latin names for ingredient listings. This information helps the formulator understand the source of the fatty portion of the surfactant. Triglycerides can be classified according to their carbon chain lengths. For instance, in Table 1 (appendix) the triglycerides are grouped by carbon chain lengths less than C-18, equal to C-18 and greater than C-18. il Preparation The process that allows for the transformation of a plant seed into a clear, lowodor oil suitable for cosmetic use is a process that we generally take for granted. The properties of the oil are determined by the plant source and the processing used (e.g. vegetable oils ). Vegetable oils are different from essential oils, which often have an attractive aroma, are not triglycerides in the same sense. Instead, they are usually isoprenoids, which indicates that they come from a different chemical pathway in plants. Isoprenoids are the largest family of natural products, with about 22,000

3 different structures known. (istory: Isoprene (2-methyl-1,3-butadiene) recognized as the basic constituent of terpenes by. Wallach (Nobel prize in chemistry, 1910). Ruzicka (N.P. in chemistry, 1939) formulated biogenic isoprene rule which hypothesized that there was such a universal isoprene precursor. Bloch and Lynen (N.P. in medicine or physiology, 1964) established the basic elucidation of the biosynthetic pathway.) n isoprene Figure 2 Pressing: Steam works well to extract essential oils like coriander oil, but it does not work well for triglyceride oils. Triglyceride and wax ester oils can be squeezed out of seeds using a turning screw that presses the mashed-up seed against a metal barrel with slits in the side. The oil and some fine particles squeeze out through the narrow slits. This operation would be called an oil expeller or seed oil press. The oil from the seed oil press can be filtered and called virgin oil, especially if it isn t heated up to get more oil out. The oil from the seed oil press can also be called crude oil. Alternatively, oil can be dissolved in solvent, which can then be evaporated, leaving the extracted oil. ften, seeds are flaked to increase surface area. The seeds are processed into thin flakes before pressing or solvent extraction. The flaking improves oil yield by breaking open the small oil pockets in the seeds. Sometimes the seeds are heated before flaking so that the proteins in the seed won t break down the oil or other things in the seeds. The preheating is also called preconditioning. The oil comes out more easily if it is hot, but excessive heat damages oil quality. Sometimes the seeds are crushed and formed into pieces called collets that have lots of holes or openings. This step also is done before solvent extraction so the oil can flow out more easily. Solvent extracted oil with some solvent still in it is called the miscella. Crude oil can usually be good enough for chemical uses. In a process called winterization, a well-filtered virgin oil can be kept cold to remove any solid waxes that might crystallize out.

4 Many cosmetics applications require cold-pressed, virgin oil. n the other hand, some seeds are too low in oil to economically remove the oil by pressing. In any case, once you have the crude oil, you can move onto refining. Refining: Refining is done by filtering the oil through clay or silica that can remove color. In an operation called degumming, alkali in water is added to the oil and some ingredients, especially fatty acids and phospholipids go into the water or settle out and are filtered. Finally, in deodorization, steam can be passed through the oil to remove odor. This step also breaks down oxygen attached to the oil, which might lower oil quality. After refining, the oil should be light in color, odorless, and have no oxygen breakdown products or solid wax. The customer s requirements for the oil in terms of color, odor and the like will determine the number of steps needed to get an acceptable product. Consequently, the amount of usable oil you have left after refining is often related not only to the amount of crude oil present in the seed, but is also related to the requirements of color, titer point and properties you impose for the final oil. Functionality: The oils that are commonly used in cosmetic products are complex mixtures of different triglycerides, but also contain various other components that are useful. For example, olive oil can be processed to contain highly desirable tocopherols, or alternatively processed to remove the tocopherols (vitamin E/α-tocopherol). If the oil is in the formulation for the benefit derived from the tocopherols, how the oil is processed is key to the functionality and usefulness of the resulting oil. Figure 3: term tocol is the trivial designation for 2-methyl-2-(4,8,12- trimethyltridecyl)chroman-6-ol (I, R1 = R2 = R3 = ) The winterizing of oils (cooling and filtration of solids) results in a loss of the higher molecular weight fractions. Many times it is exactly these fractions that provide the unique skin feel or conditioning to the product. It should be clear that the different processed used in the preparation of an oil may be critical to functionality. Cosmetic Application of ils The usage of oils, fats, butters and waxes in personal-care products per se is relatively low compared to the usage in food applications. (Figure 2-appendix)

5 The selection of oils in personal-care products is strictly governed by the functional attributes the oil confers and any desire for market claims related to the perception of the oil s benefits. This is not the case when choosing oils for making derivatives. Derivatives by far are the principal use of oils in personalcare products. In the case of derivatives, the choice of an oil is based upon cost, availability and carbon chain distribution. Dry oils: The skin and hair are major areas which oil may be applied for a beneficial effect. The exact benefit depends principally on the particular oil chosen. ils that have a very dry feel, which we classify as ultra light oils, find applications in sunscreens and massage oil, where a non-greasy feel is critical. This class of oils also finds application in aromatherapy. Light oils: Light oils have a transient conditioning effect when applied to the hair and improve comb properties, without contributing much to the bulk of the hair. Many of these oils also contribute to gloss to the hair. Intermediate oils: Intermediate oils find application in skin care as moisturizing oils and conditioners on the hair. This type of oil is used in bath oils and is recommended where a slick feel is desired. Drying oils: These oils form a film when exposed to air. The formation of film is due in large part to the presence of unsaturation in the oil. The use of drying oils is found primarily in industrial applications, like paints and varnishes, but he judicious use of these oils in personal-care applications can result in an interesting class of resin products. Drying oils include linseed oil and tung oil. These oils prossess multiple double bonds, some of which are conjugated. Functionalized oils: Functionalized oils are those oils that have organic groups other than alkyl or alkylene pendant groups. While these oils are less well known, they have unique functionality in personal-care products. For example, castor oil has a hydroxyl group present in the center of the fatty molecule. The presence of this group in the molecule gives castor oil its usefulness in making lipsticks. Derivatives The process of converting these primary ingredients into useful intermediates like acids, alcohols or methyl esters is shown (appendix, figure 3). Wax esters: Long-chained acids that have been reacted with long-chained alcohols. ther chemicals are called waxes if they possess tactile properties similar to a true wax. An example is beeswax. Polishes are a major application area for this class of materials.

6 Wax esters have two fatty groups. ne is contained in the alcohol portion of the molecule, the other is in the acid group. Esters are synthesized by the reaction of an organic acid with an organic alcohol (appendix, figure 4). Esterification is the reverse of saponification, in that ester linkages are formed. The fatty alcohol that is formed during saponification is not water-soluble. In addition, many naturally occurring waxes also contain other components, such as hydrocarbon resins that are also water-insoluble and quite inert to chemical reaction. Methyl esters: Triglycerides may be easily turned into methyl esters by reaction with methanol and catalyst. Base catalysts are preferred. As the reaction proceeds, the reaction mixture turns hazy as glycerin is liberated. nce complete, the excess methanol is distilled off, glycerin is removed from the bottom after it settles, and the methyl ester is distilled into its fractions. The methyl ester formed by the reaction, if not distilled, is still referred to by the oil name (e.g. methyl cocoate). owever once fractionated, the material is named by carbon distribution. Methyl cocoate is fractionated into methyl laurate, methyl myristate and so on. The triglyceride source is lost in the name of the methyl ester. The names are given in the appendix, table 2. Transformation into Surfactants Acids, alcohols and methyl esters are very basic building blocks from which surfactants are derived. (see appendix). The selection of a hydrophobe to prepare a surfactant is one of many factors that have a profound effect upon the final properties of the molecule. The process used to make the surfactant, the by-products, impurities and co-products are also important to functionality. The commercial processes that allow for the transformation of products into useful surfactants via various processes can produce products that have different functional properties when placed in formulations. Conclusion Factors for preparation of useful surfactants: process used to convert natural materials into derivatives, surfactants, and the skill (art) of the formulator to accommodate consumer needs.