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Issue 26 |
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| Category | Title | Author | ||
| Guest Article | New cosmetic raw materials from fats and oils | Karlheinz Hill |
Content
1. Introduction
Results from oleochemistry show that the use of vegetable fats and oils allows the development of competitive, powerful products and product concepts which are both consumer-friendly and environmentally-friendly. Recent products which fit this requirement profile are the anionic surfactants cocomonoglyceride sulfate and protein-fatty acid condensate and the nonionic sugar surfactant alkyl polyglycosides from glucose and fatty alcohol. These products are used in washing and cleansing agents, as mild surfactants in cosmetics. For personal care applications, long chain alkyl polyglycosides or composites of special glycerides and alkyl polyglycosides were shown to be interesting emulsifiers and lipid layer enhancers. New emollients for light emulsions have been developed based on fatty alcohols, e.g. dialkyl ethers and dialkyl carbo
2. Fats and oils as raw materials
The sources of oils and fats are various vegetable and animal raw materials (e.g. tallow, lard) with the vegetable raw materials soybean, palm, rapeseed and sunflower oil being the most important ones regarding the amounts involved. Of the approximately 101 million tonnes of fats and oils which were produced worldwide in 1998, by far the largest share was used in human foodstuffs. For oleochemistry, 14 million tonnes were available. The composition of the fatty acids contained in the oil (fatty acid spectrum) determines the further use of the oils. Special attention must be given to coconut oil and palm kernel oil (lauric oils) because of their high share of fatty acids with a short or medium chain length (mainly 12 and 14 carbon atoms: C12, C14). For example, these are particularly suitable for further processing to surfactants for washing and cleansing agents as well as cosmetics.
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Oils and fats are triglycerides which typically consist of glycerine and saturated and unsaturated fatty acids. There are a few exceptions from this rule, such as castor oil, a glycerol triester of 12-hydroxyoleic acid (ricinoleic acid). From a chemical point of view, triglycerides offer two reactive sites, the double bond in the unsaturated fatty acid chain and the acid group of the fatty acid chain. With regard to product development based on triglycerides the majority of derivatization reactions is carried out at the carboxylic group (> 90%) whereas oleochemical reactions involving the alkyl chain or double bond represent less than 10%.
For most of the further uses, oils and fats must be split into the so-called oleochemical base materials: fatty acid methyl esters, fatty acids, glycerol and, as hydrogenation products of the fatty acid methyl esters, fatty alcohols. In the following, innovative products, which are derived from glycerides, fatty acids or fatty alcohols are presented: surfactants, emulsifiers, and emollients.
3. Surfactants and emulsifiers (1,2)
The basic way in which surfactants act is determined by their structure. With their hydrophilic head and hydrophobic tail, surfactant molecules interpose themselves between water and water-insoluble substances. By enriching themselves at the boundaries which water forms with air or oil they lower its surface tension; as ingredients in soaps and washing agents they make contact with soiled material in this way. When dissolved in water at higher concentrations these molecules group themselves together to form spherical structures (micelles); their inwards-pointing hydrophobic groups surround soil particles and keep these in solution. Surfactants are generally classified as being anionic, cationic, nonionic or amphoteric surfactants depending on the type and charge of the hydrophilic groups.
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Surfactants are used in a wide range of fields. By far the most important field of application is the washing and cleansing sector as well as textile treatment and cosmetics; these use more than 50% of the total amount of surfactants. Surfactants are also used in the food sector, in crop protection, in mining, and in the production of paints, dyes, and paper. The basic manufacturing routes to important surfactants are layed out in Figure 1. It is true that the most important surfactant from the amount produced apart from soap is still the petrochemical-based alkyl benzene sulfonate; however, in recent years a continuous trend towards surfactants based on renewable resources has become apparent. The total worldwide market amounts to 10.7 million tonnes for the year 2000, coming from 9.2 million tonnes in 1995.
4. Cocomonoglyceride sulfate (CMGS) (3,4)
Cocomonoglyceride sulfate (CMGS) has been known for a long time and has already been used in a few products. However, the normal manufacturing methods have various disadvantages such as the use of solvents or large amounts of secondary products and, as a result, a product quality which is not optimal. In a newly developed manufacturing process CMGS is obtained directly from coconut oil in a solvent-free two-stage process. In the first stage cocomonoglyceride is obtained by simple transesterification of coconut oil with glycerol in a molar ratio of 1:2 (Figure 2). This pure vegetable raw material is converted to CMGS by reaction with sulfur trioxide (SO3) gas (1-8% v/v in air or nitrogen) in a falling-film reactor. The raw product is then neutralized with aqueous sodium hydroxide using a buffer if necessary; a certain amount of sodium sulfate (Na2SO4) is formed. If required, the salt present in the product can be reduced by membrane filtration.
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Because of its technical application properties CMGS is predestined for use in cosmetic products such as shower gels and foam baths or shampoos. Compared to ether sulfate, the standard surfactant for this application, CMGS has a similar good foaming power. Combinations of alkyl polyglycosides (APG®) and CMGS, in which CMGS acts as foam booster, are particularly interesting. The CMGS/APG mixtures additionally show an adequate thickening ability, an important criterion for the formulation of products. An acceptable viscosity is already achieved with 10% solutions without the addition of co-surfactants by using only small amounts of sodium chloride. In dermatological tests for skin compatibility (epidermis swelling test) and mucous membrane irritation (HET-CAM) CMGS proved to be considerably less of a skin irritant than ether sulfate or other anionic surfactants such as sulfosuccinates. It is comparable to very mild surfactants, such as oleylmethyltauride and betaine (cocoamidopropylbetaine). By mixing with alkyl polyglycosides the skin compatibility of CMGS can be improved further.
5. Protein-fatty acid condensates (5, 6)
In the development of the protein-fatty acid condensates it was possible to combine the renewable resources fatty acids (from vegetable oil) and protein, which can be obtained from both animal waste (leather) as well as from many plants, to construct a surfactant structure with a hydrophobic (fatty acid) and a hydrophilic (protein) part (Figure 3). This was carried out by reacting protein hydrolyzate with fatty acid chloride under Schotten-Baumann conditions, using water as solvent. Products were obtained which had an excellent skin compatibility and additionally had a good cleaning effect. The fact that even small additions of the acylated protein hydrolyzate improve the skin compatibility of other surfactants out of all proportion is important from a technical formulation point of view. An explanation for this protective effect could lie in the amphoteric behavior of the product. There is an interaction between the protein-fatty acid condensate and skin collagen. This leads to the formation of a protective layer, which reduces the excessive attack of surfactants on the upper layers of the skin, their strong degreasing effect and the direct interaction of anionic surfactants with the skin.
In the cosmetic branch, protein-based surfactants are mainly used in mild shower and bath products, mild shampoos, surfactant-based face cleansers, cold-wave preparations and fixatives or surfactant preparations for babies.
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6. Alkyl polyglycosides (APG) (7-11)
The development of surfactants based on carbohydrates and oils is the result of a product concept which is based on the exclusive use of renewable resources. In industry saccharose, glucose and sorbitol, which are available in large amounts, are used as the preferred starting raw materials. The selective functionalization of saccharose and sorbitol with fatty acids for the construction of a perfect amphiphilic structure cannot be realized in simple technical processes because of the polyfunctionality of the molecule. This is why the products offered on the market contain different amounts of mono-, di- and tri-esters and are therefore only suitable for particular applications, e.g. as emulsifiers for foodstuffs and cosmetics.
The ideal raw material for selective derivatization is glucose. Reaction with fatty alcohol produces alkyl glycosides; N-methylglucamides are prepared by reductive amination with methylamine and subsequent acylation. Both products have proved to be highly effective surfactants in washing and cleansing agents. The alkyl glycosides have also established themselves in the cosmetic products sector, as auxiliaries in crop protection formulations and as surfactants in industrial cleansing agents and today can already be said to be the most important sugar surfactants.
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Alkyl polyglycosides have been known for a long time but only now, following several years' research work, has it been possible to develop reaction conditions which allow manufacture on a commercial scale. The structure on which these compounds are based corresponds exactly to the surfactant model described above. The hydrophobic (or lipophilic) hydrocarbon chain is formed by a fatty alcohol (dodecanol/tetradecanol) obtained from palm kernel oil or coconut oil. The hydrophilic part of the molecule is based on glucose (dextrose) obtained from starch (Figures 4 and 5). The chemical challenge to process technology was to find reaction conditions which allowed fatty alcohol to react directly with glucose on a commercial scale and at an acceptable cost. In order to realize as environmentally-friendly method as possible the use of solvents was rejected.
By combining vegetable oil and sugar as raw materials it has for the first time become possible to offer commercially important amounts of nonionic surfactants which are completely based on renewable resources. Unique properties had previously been determined for alkyl polyglycosides, particularly in combination with other surfactants. For example, the use of alkyl polyglycosides in a light-duty detergent or shampoo formulation means that the total amount of surfactants can be reduced without sacrificing any performance.
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Toxicological and ecological laboratory investigations have also produced favorable results. Alkyl polyglycosides have a good compatibility with the eyes, skin and mucous membranes and even reduce the irritant effects of surfactant combinations. On top of this, they are completely biodegradable, both aerobically and anaerobically.
7. Glycerol based emulsifiers (12)
Emulsifiers based on glycerol or polyglycerol are a class of products which is well known in the market and used particularly in products for personal care and the food area. Further development will focus on the design and optimization of specific emulsifier formulations.
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The combination of different types of emulsifiers can lead to new uses for mono- and diglycerides. Polyglycerol esters are obtained by esterification of polyglycerol, which is produced by the oligomerization of glycerol under basic conditions with fatty acids. The properties of the various products can be adjusted by the type of polyglycerol used on one hand and by the chain lengths and chain type of the fatty acid used on the other hand. Selected types of products with different molecular weight are shown as an example in Table 1. For example, Dehymuls® PGPH is recommended to be used in body lotions. It leaves the skin with a smooth, non-greasy, and well-cared feeling, spreads easily, and absorbs quickly.
8. Emulsifiers based on alkyl polyglycosides and polyglycerol ester (13)
Requirements for modern emulsifiers not only include outstanding performance but also compatibility with modern emulsification techniques and balanced sensory feeling. One product which fulfills these requirements is a compound based on glycerine, alkyl polyglycoside and polyglyceryl-2-dipoly-hydroxystearate (Eumulgin® VL 75). In combination with selected emollients it allows the preparation of O/W emulsions with high quality and stability (small droplet sizes). In addition, due to the liquid appearance of the product, and, as a consequence, the possibility for cold processing, the manufacturing time and costs for the preparation of emulsions is significantly reduced (Figure 6).
9. Multifunctional care additives based on alkyl polyglycosides and glyceryl oleate (14)
The intelligent combination of alkyl polyglycosides and glyceryl oleate resulted in a new product which combines emulsifying and cleansing properties with outstanding care effects, such as enhancing of the skin lipid layer. This effect is proven in a standardized test by washing the fore arm, rinsing, drying and extracting the lipid layer on the skin with ethanol pads (Figure 7). The lipid content is measured by quantitative analysis of glycerol oleate in the extract (Figure 8). Technical data of the product (Lamesoft® PO 65) are summarized in Table 2.
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Dioctyl
carbonate Cetiol ® CC
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| INCI: | Dicaprylyl Carbonate |
| Spreading value: | 1600 mm² / 10 min |
| Sensory feeling: | dry, volatile silicon oil like |
| Skin compatibility: | excellent |
| Stability: | hydrolysis stable |
| Origin: | vegetable (fatty alcohol) |
| Biodegradability: | yes |
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Figure 9: see enlarged version |
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10. Dialkyl carbonates as emollients (15)
The physico-chemical nature of the oil phase components in a cosmetic emulsion, the emollients, determines their skin-care effects, such as smoothing, spreading, and sensorial appearance. Test methods have been developed to characterize and classify the numerous emollients available on the market. Selected examples of different chemical structures are listed in Table 3. However, especially with regard to additional effects, there is still a demand for new and better performing products. One example of a recent development is dicaprylyl carbonate (Cetiol® CC), synthesized by the trans-esterification reaction of octanol and dimethyl carbonate in the presence of alkali catalyst (Table 4). In addition to the very high spreading values it could be shown that Cetiol® CC is a very good solvent for solid UV-filters, which makes this product unique in its overall properties compared to other common emollients (Figure 9).
11. Summary
With the examples of recent product innovations from oleochemistry the successful development of environmentally compatible and powerful products in the sense of a sustainable development has been demonstrated. It can be assumed that in future further possibilities for using renewable resources will continue to be sought for in an ever-increasing manner. Here the combination of different vegetable raw material classes to form new products or tailor made combinations of various new and existing products to obtain multifunctionality and intelligent product concepts in order to meet market and consumer needs will be a challenge for research and development.
(APG, Cetiol, Dehymuls, Eumulgin, Eutanol, Lamecreme, Lameform, Lamesoft, Myritol are registered trademarks of Cognis.)
12. References
1. Falbe, J. (Ed.): Surfactants in Consumer Products: Theory, Technology, Applications, Springer, Heidelberg, 1987.
2. W. Dolkemeyer: Surfactants on the Eve of the Third Millennium, 5th World Surfactant Congress, Cesio 2000, Florence May 29 - June 02, 2000.
3. Behler, A., Hensen, H., Vier, J.: Kokosmonoglyceridsulfat - ein Aniontensid für kosmetische Formulierungen, Fett/Lipid 98 (1996), 309.
4. Behler, A., Hensen, H., Vier, J.: Cocomonoglyceride Sulfate - An Anionic Surfactant for Cosmetic Formulations, Henkel Referate 33 (1997), 7.
5. Sander, A., Eilers, E., Heilemann, A., von Kries, E.: Herstellung und Anwendungsmöglichkeiten von Eiweiß-Fettsäurekondensaten, Fett/Lipid 99 (1997), 115.
6. Sander, A., Eilers, E., Heilemann, A., von Kries, E.: Production and Application of Protein/Fatty Acid Condensates, Henkel-Referate 34 (1998), 14.
7. Biermann, M., Schmid, K., Schulz, P.: Alkylpolyglucoside - Technologie und Eigenschaften, Starch/Stärke 45 (1993), 281.
8. Knaut, J., G. Kreienfeld: Alkyl Polyglycosides. A New Surfactant Class based on Renewable Raw Materials, Chimica Oggi 1993, 41.
9. Hill, K., von Rybinski, W., Stoll, G. (Eds.): Alkyl Polyglycosides - Technology, Properties and Applications, VCH, Weinheim, 1997.
10. von Rybinski, W., K. Hill: Alkyl Polyglycosides - Properties and Applications of a new Class of Surfactants, Angew. Chem. Int. Ed. 37 (1998), 1328; Angew. Chem. 110 (1998), 1394.
11. K. Hill, O. Rhode: Carbohydrate-based surfactants, Fett/Lipid 101 (1999), 25.
12. Tesmann, H.: Nachwachsende Rohstoffe in der Kosmetik, in Perspektiven nachwachsender Rohstoffe in der Chemie (Eierdanz, H., Ed.), VCH, Weinheim, 1996, pp. 31-39.
13. Kawa, R., Ansmann, A., Jackwerth, B., Leonard, M.: Das Synergistic-Sun-Systems-Konzept, Parfüm. Kosmet. 80 (1999), 17.
14. Förster, Th., Issberner, U., Hensen, H.: Lipid/Surfactant Compounds as a New Tool to Optimize Skin-Care Properties of Personal-Cleansing Products, J. Surfactants and Detergents 3 (2000), 345.
Author
Dr. Karlheinz Hill
Karlheinz Hill joined Henkel, Duesseldorf in 1986 as a research chemist and in 1999 assumed the position of head of Research Organic Products at Cognis. Since July 2000 he has been head of Care Chemicals Technology at Cognis.
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