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  • 1. title: Surfactants in Cosmetics Surfactant Science Series ; V. 68 author: Rieger, Martin M. publisher: CRC Press isbn10 | asin: 0824798058 print isbn13: 9780824798055 ebook isbn13: 9780585373423 language: English subject Surface active agents, Cosmetics. publication date: 1997 lcc: TP994.S8763 1997eb ddc: 668/.55 subject: Surface active agents, Cosmetics.
  • 2. Surfactants in Cosmetics
  • 3. SURFACTANT SCIENCE SERIES CONSULTING EDITORS MARTIN J. SCHICK Consultant New York, New York FREDERICK M. FOWKES (19151990) 1. Nonionic Surfactants, edited by Martin J. Schick (see also Volumes 19, 23, and 60) 2. Solvent Properties of Surfactant Solutions, edited by Kozo Shinoda (see Volume 55) 3. Surfactant Biodegradation, R. D. Swisher (see Volume 18) 4. Cationic Surfactants, edited by Eric Jungermann (see also Volumes 34, 37, and 53) 5. Detergency: Theory and Test Methods (in three parts), edited by W. G. Cutler and R. C. Davis (see also Volume 20) 6. Emulsions and Emulsion Technology (in three parts), edited by Kenneth J. Lissant 7. Anionic Surfactants (in two parts), edited by Warner M. Linfield (see Volume 56) 8. Anionic Surfactants: Chemical Analysis, edited by John Cross (out of print) 9. Stabilization of Colloidal Dispersions by Polymer Adsorption, Tatsuo Sato and Richard Ruch (out of print) 10. Anionic Surfactants: Biochemistry, Toxicology, Dermatology, edited by Christian Gloxhuber (see Volume 43) 11. Anionic Surfactants: Physical Chemistry of Surfactant Action, edited by E. H. Lucassen- Reynders (out of print) 12. Amphoteric Surfactants, edited by B. R. Bluestein and Clifford L. Hilton (see Volume 59) 13. Demulsification: Industrial Applications, Kenneth J. Lissant (out of print) 14. Surfactants in Textile Processing, Arved Datyner 15. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications, edited by Ayao Kitahara and Akira Watanabe 16. Surfactants in Cosmetics, edited by Martin M. Rieger (out of print) 17. Interfacial Phenomena: Equilibrium and Dynamic Effects, Clarence A. Miller and P. Neogi
  • 4. 18. Surfactant Biodegradation: Second Edition, Revised and Expanded, R. D. Swisher 19. Nonionic Surfactants: Chemical Analysis, edited by John Cross
  • 5. 20. Detergency: Theory and Technology, edited by W. Gale Cutler and Erik Kissa 21. Interfacial Phenomena in Apolar Media, edited by Hans-Friedrich Eicke and Geoffrey D. Parfitt 22. Surfactant Solutions: New Methods of Investigation, edited by Raoul Zana 23. Nonionic Surfactants: Physical Chemistry, edited by Martin J. Schick 24. Microemulsion Systems, edited by Henri L. Rosano and Marc Clausse 25. Biosurfactants and Biotechnology, edited by Naim Kosaric, W. L. Cairns, and Neil C. C. Gray 26. Surfactants in Emerging Technologies, edited by Milton J. Rosen 27. Reagents in Mineral Technology, edited by P. Somasundaran and Brij M. Moudgil 28. Surfactants in Chemical/Process Engineering, edited by Darsh T. Wasan, Martin E. Ginn, and Dinesh O. Shah 29. Thin Liquid Films, edited by I. B. Ivanov 30. Microemulsions and Related Systems: Formulation, Solvency, and Physical Properties, edited by Maurice Bourrel and Robert S. Schechter 31. Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato 32. Interfacial Phenomena in Coal Technology, edited by Gregory D. Botsaris and Yuli M. Glazman 33. Surfactant-Based Separation Processes, edited by John F. Scamehorn and Jeffrey H. Harwell 34. Cationic Surfactants: Organic Chemistry, edited by James M. Richmond 35. Alkylene Oxides and Their Polymers, F. E. Bailey, Jr., and Joseph V. Koleske 36. Interfacial Phenomena in Petroleum Recovery, edited by Norman R. Morrow 37. Cationic Surfactants: Physical Chemistry, edited by Donn N. Rubingh and Paul M. Holland 38. Kinetics and Catalysis in Microheterogeneous Systems, edited by M. Grätzel and K. Kalyanasundaram 39. Interfacial Phenomena in Biological Systems, edited by Max Bender 40. Analysis of Surfactants, Thomas M. Schmitt 41. Light Scattering by Liquid Surfaces and Complementary Techniques, edited by
  • 6. Dominique Langevin 42. Polymeric Surfactants, Irja Piirma 43. Anionic Surfactants: Biochemistry, Toxicology, Dermatology. Second Edition, Revised and Expanded, edited by Christian Gloxhuber and Klaus Künstler 44. Organized Solutions: Surfactants in Science and Technology, edited by Stig E. Friberg and Björn Lindman 45. Defoaming: Theory and Industrial Applications, edited by P. R. Garrett 46. Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe 47. Coagulation and Flocculation: Theory and Applications, edited by Bohuslav Dobias *
  • 7. 48. Biosurfactants: Production · Properties · Applications, edited by Naim Kosaric 49. Wettability, edited by John C. Berg 50. Fluorinated Surfactants: Synthesis · Properties · Applications, Erik Kissa 51. Surface and Colloid Chemistry in Advanced Ceramics Processing, edited by Robert J. Pugh and Lennart Bergström 52. Technological Applications of Dispersions, edited by Robert B. McKay 53. Cationic Surfactants: Analytical and Biological Evaluation, edited by John Cross and Edward J. Singer 54. Surfactants in Agrochemicals, Tharwat F. Tadros 55. Solubilization in Surfactant Aggregates, edited by Sherril D. Christian and John F. Scamehorn 56. Anionic Surfactants: Organic Chemistry, edited by Helmut W. Stache 57. Foams: Theory, Measurements, and Applications, edited by Robert K. Prud'homme and Saad A. Khan 58. The Preparation of Dispersions in Liquids, H. N. Stein 59. Amphoteric Surfactants: Second Edition, edited by Eric G. Lomax 60. Nonionic Surfactants: Polyoxyalkylene Block Copolymers, edited by Vaughn M. Nace 61. Emulsions and Emulsion Stability, edited by Johan Sjöblom 62. Vesicles, edited by Morton Rosoff 63. Applied Surface Thermodynamics, edited by A. W. Neumann and Jan K. Spelt 64. Surfactants in Solution, edited by Arun K. Chattopadhyay and K. L. Mittal 65. Detergents in the Environment, edited by Milan Johann Schwuger 66. Industrial Applications of Microemulsions, edited by Conxita Solans and Hironobu Kunieda 67. Liquid Detergents, edited by Kuo-Yann Lai 68. Surfactants in Cosmetics: Second Edition, Revised and Expanded, edited by Martin M. Rieger and Linda D. Rhein 69. Enzymes in Detergency, edited by Jan H. van Ee, Onno Misset, and Erik J. Baas ADDITIONAL VOLUMES IN PREPARATION StructurePerformance Relationships in Surfactants, edited by Kunio Esumi and Minoru
  • 8. Ueno Powdered Detergents, edited by Michael S. Showell
  • 9. Page i Surfactants in Cosmetics Second Edition, Revised and Expanded Edited by Martin M. Rieger M & A Rieger Associates Morris Plains, New Jersey Linda D. Rhein Johnson & Johnson Consumer Products Skillman, New Jersey
  • 10. Page ii Library of Congress Cataloging-in-Publication Data Surfactants in cosmetics. 2nd ed., rev. and expanded / edited by Martin M. Rieger and Linda D. Rhein. p. cm. (Surfactant science series ; v. 68) Includes index. ISBN 0-8247-9805-8 (hc : alk. paper) 1. Surface active agents. 2. Cosmetics. I. Rieger, Martin M., II. Rhein, Linda D. III. Series. TP994.S8763 1997 668'.55dc21 97-57 CIP The publisher offers discounts on this book when ordered in bulk quantities. For more information, write to Special Sales/Professional Marketing at the address below. This book is printed on acid-free paper. Copyright © 1997 by Marcel Dekker, Inc. All Rights Reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher. Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 Current printing (last digit): 10 9 8 7 6 5 4 3 2 PRINTED IN THE UNITED STATES OF AMERICA
  • 11. Page iii Preface to the Second Edition The need for surfactants in consumer acceptable cosmetic products formed the stimulus for the preparation of the first edition of Surfactants in Cosmetics ten years ago. Since that time much progress has been made in creating novel surfactants for the personal care industry and in understanding the fundamental behavior of surfactants in solution and their interactions with skin. More importantly, there has been steady movement toward the selection of surfactants for cosmetics that have no objective adverse impact on human skin and elicit noor at most minimalnegative subjective reaction. Thus, this second edition not only reflects the search for milder surfactants but also presents up-to- date information on the activity of mixtures that interact in solution and on the skin to enhance perceived as well as absolute safety. In addition, this edition updates the everchanging nomenclature of surfactants in the cosmetic industry and relies on International Nomenclature Cosmetic Ingredient (INCI) names and designations, as provided in the sixth edition of the International Cosmetic Ingredient Dictionary (available from the Cosmetics, Toiletries, and Fragrance Association in Washington, D.C.). The editors determined early on that the scientific information presented in the first edition of Surfactants in Cosmetics remains valid. In order to avoid unnecessary repetition and unwanted redundancy, the editors decided to depend primarily on a new set of authors and to select alternative topics for the second edition. As a result, the second edition provides a unique and novel aspect of the topic of surfactants in cosmetics. Readers are urged to view the second edition not as a replacement for the first but as an extension and an addition. The table of contents from the first edition is therefore included to assist readers in their endless search for information. The first three chapters of this book address the fundamentals of surfactants, with emphasis on their uses in cosmetics. These chapters provide the basic science required for the effective use of surfactants. Chapters 49 discuss the current status of research on the application of surfactants
  • 12. Page iv in cosmetic emulsions. Chapters 1012 introduce the reader to microemulsions and vesicles. These nine chapters are intended to help in the formulation of cosmetic products. Chapters 1317 provide current information on surfactant usage in the formulation of various types of cosmetic products, and chapters 1825 deal with the critical topic of the interaction of surfactants with the skin. Chapters 1325 mayat timesappear to cover similar topics, primarily because this material is of great interest and is often viewed from varied perspectives. The last three chapters cover topics of importance to practitioners which result from the use of surfactants in cosmetic products. The editors thank the authors for their contributions and for accepting our editorial suggestions with alacrity. We regretfully note that Dr. Morton Pader passed away shortly after submitting his contribution. The editors also recognize with deep appreciation the help provided by the staff of the publisher. As noted, the second edition differs materially from the first edition, and it is hoped that readers will find the book useful and of current and continuing interest. MARTIN M. RIEGER LINDA D. RHEIN
  • 13. Page v Preface to the First Edition The monetary value of worldwide sales of cosmetics and toiletries is extremely large; however, the value of these consumer products might better be measured in terms of their psychological and health benefits and their impact on our daily lives. Most modern cosmetic preparations could not be produced without the use of a variety of surfactants, and it is appropriate, therefore, to devote a volume to this topic in the Surfactant Science series. The editor of a collective volume, such as this one, establishes the book's objectives, which in turn determine its makeup and contents. It is the principal purpose of this volume to provide a comprehensive survey of the use of surfactants in cosmetics. The reader can expect to find specific information on all types of surfactants used in cosmetics and toiletries and, equally important, references to the vast original literature on this subject. More specifically, the goal of this book is to provide answers to some pertinent questions such as those listed below: What surfactants are used in cosmetics? Why are surfactants required in cosmetics? What functions are served by surfactants in cosmetics? How are surfactants used in cosmetics? What problems are caused by the use of surfactants in cosmetics? What interactions take place between surfactants in cosmetics and the substrate, i.e., the skin and its appendages? It should be noted that there are some omissions in this text; these are intentional. We are attempting to avoid redundancy from chapter to chapter in this book and also within the Surfactant Science series, which now includes about 21 books. Thus, details of the complex chemistry of the surfactants are deliberately excluded since this subject is expertly covered in other volumes in the series. Also avoided is the use of (the ever
  • 14. Page vi changing) commercial or trade names for surfactants. Instead, the nomenclature employed in the current issue (1982) of the CTFA Cosmetic Ingredient Dictionary is used extensively. Last but not least, an effort is made not to create an assembly of recipes for the preparation of cosmetic formulations; the few formulations included are presented only for illustrative purposes. The editor sincerely hopes that these goals have been achieved. The editor also hopes that readers of the book will find it not only scientifically useful but readable as well. Special thanks are due to the authors of the various chapters who have patiently endured the need for editorial changes and the unavoidable delays incurred in a multi-authored book. Thanks are also due the Cosmetic, Toiletries, and Fragrance Association which granted permission to utilize CTFA surfactant nomenclature as well as many ingredient descriptions from the Cosmetic Ingredient Dictionary. Finally, gratitude is expressed to my faithful secretaries, Ms. G. Pilewski and Ms. G. Salmon, and to the editorial staff of Marcel Dekker without whose help this book could not have been produced. MARTIN M. RIEGER
  • 15. Page vii Contents of the Second Edition Preface to the Second Edition iii Preface to the First Edition v Contents of the First Edition xi Contributors xiii 1. Surfactant Chemistry and Classification Martin M. Rieger 1 2. Physical Properties of Surfactants Used in Cosmetics Drew Myers 29 3. The Analysis of Surfactants in Cosmetics Jane M. Eldridge 83 4. Principles of Emulsion Formation Thomas Förster 105 5. Emulsifier Selection/HLB Donald L. Courtney, Sr. 127 6. Multiple Emulsions in Cosmetics Monique Seiller, Francis Puisieux, and J. L. Grossiord 139 7. Multiphase Emulsions H. E. Junginger 155 8. Stability of Emulsions Christopher D. Vaughan 183
  • 16. Page viii 9. Phase Inversion in Emulsions: CAPICOConcept and Application Armin Wadle, Holger Tesmann, Mark Leonard, and Thomas Förster 207 10. Solubilization in Cosmetic Systems Stig E. Friberg and Jiang Yang 225 11. Selection of Solubilizers Francesc Comelles and Carles Trullás 237 12. Liposomes and Niosomes Daniel D. Lasic 263 13. Surfactants for Skin Cleansers Paul Thau 285 14. Cleansing Bars for Face and Body: In Search of Mildness Richard I. Murahata, M. P. Aronson, Paul T. Sharko, and Alan P. Greene 307 15. Topical Antibacterial Wash Products Boyce M. Morrison, Jr., Diana D. Scala, and George E. Fischler 331 16. Hair Cleansers Charles Reich 357 17. Surfactants in Dental Products Morton Pader 385 18. In Vitro Interactions: Biochemical and Biophysical Effects of Surfactants on Skin Linda D. Rhein 397 19. Surfactant Mildness Genji Imokawa 427 20. Surfactant Effects on Skin Barrier William Abraham 473 21. Bioengineering Techniques for Investigating the Effects of Surfactants on Skin Perveen Y. Rizvi, Gary L. Grove, and Boyce M. Morrison, Jr. 489 22. Skin Penetration Enhancement by Surfactants Joel L. Zatz and Belinda Lee 501
  • 17. 23. Human in Vivo Methods for Assessing the Irritation Potential of Cleansing Systems F. Anthony Simion 519 24. The Challenge of Using the ''Inarticulate" Consumer As an R & D Partner in Cosmetic Product Development David W. Ingersoll 533
  • 18. Page ix 25. Toxicology of Surfactants Used in Cosmetics Walter Sterzel 557 26. Chemical Instability of Surfactants Martin M. Rieger 573 27. Inactivation of Preservatives by Surfactants Donald S. Orth 583 28. Solubilization of Fragrances by Surfactants John N. Labows, John C. Brahms, and Robert H. Cagan 605 Index 621
  • 19. Page xi Contents of the First Edition 1. Surfactants for Cosmetic Macroemulsions: Properties and Application Bernard Idson 1 2. Microemulsions and Application of Solubilization in Cosmetics T. Joseph Lin 29 3. Surfactant Association Structures of Relevance to Cosmetic Preparations Stig E. Friberg and Magda A. El-Nokaly 55 4. Low-Energy Emulsification T. Joseph Lin 87 5. Surfactant Analysis in Cosmetic Preparations Donald E. Deem 103 6. Interaction of Surfactants with Epidermal Tissues: Biochemical and Toxicological Aspects Edward J. Singer and Eugene P. Pittz 133 7. Interaction of Surfactants with Epidermal Tissues: Physicochemical Aspects Eugene R. Cooper and Bret Berner 195 8. Surfactants and the Preservation of Cosmetic Preparations Karl Heinz Wallhäusser 211
  • 20. Page xii 9. Surfactants in Shampoos Graham Barker 251 10. Surfactants in Oral Hygiene Products Morton Pader 293 11. Surfactants for Skin Cleansers Paul Thau 349 12. The Role of Surfactants in Aerosols Hans Breuer 377 13. Surfactants in Cosmetic Suspensions Charles Fox 401 14. Index to Surfactant Structures and CTFA Nomenclature Martin M. Rieger 431
  • 21. Page xiii Contributors William Abraham Research and Development, CYGNUS, Inc., Redwood City, California M. P. Aronson Personal Washing Research, Unilever Research Laboratory Port Sunlight, Merseyside, United Kingdom John C. Brahms Research and Development, Colgate-Palmolive Company, Piscataway, New Jersey Robert H. Cagan Research and Development, Colgate-Palmolive Company, Piscataway, New Jersey Francesc Comelles Surfactant Technology, Centro de Investigación y Desarrollo, Barcelona, Spain Donald L. Courtney, Sr. Emulsions REZ, Landenberg, Pennsylvania Jane M. Eldridge Analytical Services, Rhône-Poulenc, Inc., Cranbury, New Jersey George E. Fischler Analytical Sciences/Microbiology, Colgate-Palmolive Company, Piscataway, New Jersey Thomas Förster Chemical Research, Henkel KGaA, Düsseldorf, Germany Stig E. Friberg Department of Chemistry, Clarkson University, Potsdam, New York Alan P. Greene Personal Washing Product Development, Lever Brothers Company, Edgewater, New Jersey J. L. Grossiord Physique Pharmaceutique, Université de Paris-Sud, Châtenay-Malabry, France
  • 22. Page xiv Gary L. Grove KGL's Skin Study Center, Broomall, Pennsylvania Genji Imokawa Biological Science Laboratories, Kao Corporation, Haga, Tochigi, Japan David W. Ingersoll Consumer and Marketing Research, Givaudan-Roure, Teaneck, New Jersey H. E. Junginger Department of Pharmaceutical Technology, Leiden/Amsterdam Center for Drug Research, Leiden, The Netherlands John N. Labows Research and Development, Colgate-Palmolive Company, Piscataway, New Jersey Daniel D. Lasic Consultant, Drug and Gene Delivery Consultations, Newark, California Belinda Lee Skin Research, Colgate-Palmolive Company, Piscataway, New Jersey Mark Leonard COSPHA, Henkel Organics, Belvedere, Kent, England Boyce M. Morrison, Jr. Skin Clinical Investigations, Colgate-Palmolive Company, Piscataway, New Jersey Richard I. Murahata Clinical and Appraisal Science, Unilever Research U.S., Edgewater, New Jersey Drew Myers Consultant, Rio Tercero, Córdoba, Argentina Donald S. Orth Research and Development, Neutrogena Corporation, Los Angeles, California Morton Pader* Consumer Products Development Resources, Inc., Teaneck, New Jersey Francis Puisieux Physico-Chimie-Pharmacotechnie-Biopharmacie, Université de Paris-Sud, Châtenay-Malabry, France Charles Reich Advanced Technology/Hair Care, Colgate-Palmolive Company, Piscataway, New Jersey Linda D. Rhein World Wide Therapeutic Skin Care, Johnson & Johnson Consumer Products, Skillman, New Jersey Martin M. Rieger Consultant, M & A Rieger Associates, Morris Plains, New Jersey Perveen Y. Rizvi Skin Clinical Investigations, Colgate-Palmolive Company, Piscataway, New Jersey *Deceased.
  • 23. Page xv Diana D. Scala Skin Clinical Investigations, Colgate-Palmolive Company, Piscataway, New Jersey Monique Seiller Physico-Chimie-Pharmacotechnie-Biopharmacie, Université de Paris-Sud, Châtenay-Malabry, France Paul T. Sharko Personal Washing Product Development, Lever Brothers Company, Edgewater, New Jersey F. Anthony Simion Research and Development, The Andrew Jergens Company, Cincinnati, Ohio Walter Sterzel Department of Toxicology, Henkel KGaA, Düsseldorf, Germany Holger Tesmann CFTCOSPHA, Henkel KGaA, Düsseldorf, Germany Paul Thau Technology Surveillance, Cosmair, Inc., Clark, New Jersey Carles Trullás Research Department, Laboratories Isdin, Barcelona, Spain Christopher D. Vaughan SPF Consulting Labs, Inc., Ft. Lauderdale, Florida Armin Wadle Product Development Skin CareCOSPHA, Henkel KGaA, Düsseldorf, Germany Jiang Yang Surfactants and Specialties North America, Rhône-Poulenc, Inc., Cranbury, New Jersey Joel L. Zatz Department of Pharmaceutics, Rutgers University College of Pharmacy, Piscataway, New Jersey
  • 24. Page 1 1 Surfactant Chemistry and Classification Martin M. Rieger Consultant, M & A Rieger Associates, Morris Plains, New Jersey I. Introductory Comments 1 A. Definitions and Structural Requirements 1 B. Utility and Selection of Surfactants in Cosmetics 2 C. Classification 3 D. Nomenclature 3 II. Group Description 4 A. Amphoterics 4 B. Anionics 6 C. Cationics 15 D. Nonionics 19 References 28 I Introductory Comments A Definitions and Structural Requirements The term surfactant is shorthand for the more cumbersome "surface active agent." Surfactants as a group have the ability to modify the interface between various phases. Their effects on the interface are the result of their ability to orient themselves in accordance with the polarities of the two opposing phases. Thus the polar (hydrophilic) part of the surfactant molecule can be expected to be oriented toward the more polar (hydrophilic) phase at a given interfacial contact site. Similarly, the nonpolar (lipophilic) portion of the surfactant molecule should contact the nonpolar (lipophilic) phase. Each surfactant molecule has a tendency to reach across (bridge) the two phases, and such substances have, therefore, also been called amphiphilic. One of the prerequisites for an amphiphilic molecule is possession of at least one polar
  • 25. Page 2 and at least one essentially nonpolar portion. The orientation of a 1,2-dodecanediol molecule at a mineral-oil/water interface is readily predictable from the preceding discussion, but the positioning of 1,12-dodecanediol at a similar interface is not as obvious; it would be expected to be different and more complex than that of the 1,2- isomer. Despite their chemical similarity, the surfactant activities of these two compounds can be expected to be different. It is apparent from this that a surfactant's behavior or utility, e.g., as an emulsion stabilizer, is unrelated to its empirical formula. Instead, a surfactant's spatial configuration, i.e., the molecule's structure, plays a critical role in determining its application in cosmetics. B Utility and Selection of Surfactants in Cosmetics Those who require and use surfactants tend to define surfactants on the basis of performance. Regardless of diverse theoretical considerations, practicing cosmetic formulators have developed a usage classification that they find practical in their day-to- day activities. As a rule, a surfactant is soluble in at least one of the contacting phases and is used to perform one or more of the following tasks: Clean (Detergency), Wet, Emulsify, Solubilize, Disperse, or Foam. Surfactants are useful for creating a wide variety of dispersed systems, such as suspensions and emulsions. They cleanse and solubilize and are required not only during manufacture but are also essential for maintaining an acceptable level of physical stability of thermodynamically unstable systems, such as emulsions. Few modern cosmetic products exist that do not depend on one or more surfactants to create and maintain their desired characteristics. It is the practitioner's responsibility to select one or more surfactants that can perform the task at hand. As a result of prior experience, formulators usually can identify those surfactant structures that can be expected to be most useful for achieving the desired goal. The cosmetic formulator's choice of surfactants is more limited than that of the industrial chemist. Some of the criteria influencing selection are briefly noted below: SafetyAdverse reactions to any surfactant used in a finished cosmetic must be minimized. Odor and ColorOdoriferous or deeply colored surfactants can affect the esthetics of a finished product and should be avoided.
  • 26. PurityImpurities present in some surfactants may make the surfactant unacceptable for cosmetic use. Despite these and other limitations and the obvious requirement of cost, the cosmetic chemist must make a selection from about 2000 different commercially available surfactants. The selection for the specific formulation task requires insight into the general
  • 27. Page 3 chemical characteristics of surfactants (this chapter) and an understanding of the physichochemical behavior of these amphiphiles (Chapter 2). C Classification Classification or categorization of the thousands of different surfactants on the basis of generally recognized principles is clearly desirable. Thus it would appear practical to base such a scheme on the surfactant's functionality. Creating groupings based on such functional groups could in all likelihood be made without regard to commonly accepted chemical or physical characteristics. A typical functional scheme was developed in the CTFA (Cosmetic Ingredient Handbook) [1] by creating six functional categories for surfactants: Surfactants, Cleansing Agents Surfactants, Emulsifying Agents Surfactants, Foam Boosters Surfactants, Hydrotropes Surfactants, Solubilizing Agents Surfactants, Suspending Agents An entirely different means for classification might be based on the nature of the hydrophobic portions of surfactants. Such a classification would create groups based on the presence of hydrophobes derived from paraffinic, olefinic, aromatic, cycloaliphatic, or heterocyclic hydrophobes. This type of classification could be of particular interest to specialists who may wish to compare substances on the basis of physiological effects related to the origin of the lipophilic constituents. The most useful and widely accepted classification is based on the nature of the hydrophilic segment of the surfactant molecules. This classification system has universal acceptance and has been found to be practical throughout the surfactant industry. This approach creates four large groups of chemicals: amphoterics, anionics, cationics, and nonionics. This system categorizes surfactants on the basis of their ionic or nonionic character, does not consider differences in the hydrophobic (nonpolar) segment, and ignores functionality. It is common practice to depict surfactant molecules as ball and stick figures: In this cartoon, the hydrophobe is represented by a stick; the ball represents the hydrophilic grouping, which may carry a positive and/or a negative charge or no charge; X represents the counter ion required for electroneutrality of the molecule.
  • 28. D Nomenclature The nomenclature of surfactants can become very complex and confusing. For the purpose of labeling of cosmetics in accordance with U.S. regulation, the Cosmetics,
  • 29. Page 4 Toiletry and Fragrance Association has created names for cosmetic ingredients. It is likely that these names will soon be accepted in many other countries in the hope that a worldwide agreement on this INCI* nomenclature can be reached between governmental regulatory agencies and the trade associations concerned with cosmetics. Rules for creating these names are included in the International Cosmetic Ingredient Dictionary [2]. The names are intended to be descriptive for laypersons as well as the more technically oriented. The assigned names are not as precise as the names assigned by Chemical Abstracts and eliminate the need for using proprietary trade names. The INCI names are used in this chapter wherever possible. Some abbreviations used in the text are identified below: DEA EO HLB MEA POE or PEG PPG TEA Diethanolamine Ethylene Oxide Hydrophile/Lipophile Balance Monoethanolamine Polyoxyethylene Polyoxypropylene Triethanolamine II Group Description A Amphoterics Surfactants are classified as amphoteric ifand only ifthe charge(s) on the hydrophilic head change as a function of pH. Such surfactants must carry a positive charge at low pH and a negative charge at high pH and may form internally neutralized ionic species (zwitterions) at an intermediate pH. These features of amphoterics are illustrated below with the behavior of lauraminopropionic acid at various pH levels: Low pH: The surfactant molecule is a cation. Intermediate pH: The surfactant molecule is a zwitterion. High pH: The surfactant molecule is an anion. In this example, R represents the lauryl alkyl group, while X and C+ are the required
  • 30. counter ions. The behavior of this substance must be compared with that of lauryl betaine: Low pH: The surfactant molecule is a cation. Intermediate pH: The surfactant molecule may be a zwitterion. *INCI = International Nomenclature Cosmetic Ingredient
  • 31. Page 5 Lauryl betaine contains a quaternary nitrogen atom regardless of pH. The ionization of the carboxylic acid group is, however, pH dependent, and internal compensation is possible. Lauryl betaine is properly classified as a quaternary surfactant. In cosmetic usage, betaines and related molecules exhibit some functions associated with amphoterics. Although some authorities have at times classified betaines as amphoterics, they are classified here as quaternaries. The hydrophilic groups in amphoterics commonly are primary, secondary, or tertiary amino groups and an ionizable acidic group, i.e., COO, , or rarely on the same molecule. Two types of amphoterics exist: A 1. Alkylamido Alkyl Amines A 2. Alkyl Substituted Amino Acids A. 1 Alkylamido Alkyl Amines These substances are synthesized by acylation of the primary amino group of aminoethyl ethanolamines (NH2CH2CH2NHCH2CH2OH) with a long chain (fatty) acid derivative. The resulting cyclic 2-alkyl hydroxyethyl imidazoline is hydrolyzed in the subsequent alkylation step with chloroacetic acid or ethylacrylate to yield a complex mixture of mono- or dicarboxy alkyl derivatives: Alkylation with, for example, hydroxypropylsulfonic acid, yields a more complex tertiary amine. Commercial products are mixtures containing soaps and the hydrolysis product of the alkylating agent. They are sold as salts (usually sodium) or as free acids. At or near neutral pH they may exist in zwitterionic form. The amide linkage in these molecules may be subject to hydrolysis, but no report of chemical instability in cosmetics has been published. Alkylamido alkyl amines are generally water soluble and are compatible with most other cosmetically useful surfactants. They reportedly reduce the tendency of anionics to elicit eye irritation without significantly interfering with their foaming characteristics. These amphoterics exhibit substantivity to hair and skin proteins and act as conditioning
  • 32. and antistatic agents. Their primary use is in shampoos and miscellaneous skin cleansers. They are, however, not widely used as detersive surfactants (cleansing agents) and are not effective emulsifying agents.
  • 33. Page 6 A. 2 Alkyl Substituted Amino Acids Alkyl substituted amino acids are prepared by alkylation of various synthetic and natural amino acids or by the addition of an amine to an a, b unsaturated alkanoic acid. Some typical structures follow: As a group, these compounds exhibit excellent stability under conditions of cosmetic use. Alkyl substituted amino acids foam copiously, especially above their isoelectric point. At low pH levels they behave as cationics and foam poorly. They can be used as emulsifiers. As amphoterics, they are substantive to hair and find their most important uses in various hair coloring and hair conditioning products. B Anionics All surfactants in which the hydrophilic head of the molecule carries a negative charge are classified as anionics. The group of anionic surfactants includes types of great industrial importance and substances widely used in cosmetics. As a rule, they are inactivated or even form complex precipitates in the presence of cationic surfactants. This complexation is generally attributed to salt formation in which the ionized species react in stoichiometric proportions. The complexes may be solubilized in aqueous systems containing large amounts of anionics. For the sake of classification, anionic surfactants may be subdivided into five major chemical classes and subgroups: B. 1. Acylated Amino Acids and Acyl Peptides B. 2. Carboxylic Acids (and Salts) B. 2. (a) Alkanoic Acids B. 2. (b) Ester-functional Carboxylic Acids B. 2. (c) Ether-functional Carboxylic Acids B. 3. Sulfonic Acid Derivatives B. 3. (a) Taurates B. 3. (b) Isethionates
  • 34. B. 3. (c) Alkylaryl Sulfonates B. 3. (d) Olefin Sulfonates B. 3. (e) Sulfosuccinates B. 3. (f) Miscellanous Sulfonates B. 4. Sulfuric Acid Derivatives B. 4. (a) Alkyl Sulfates B. 4. (b) Alkyl Ether Sulfates B. 5. Phosphoric Acid Derivatives
  • 35. Page 7 The members of these five classes form water soluble salts with alkali metals and low molecular weight amines, especially alkanol amines. The members of subgroups B.1 and B.2 above depend on ionization of the carboxylic acid group for aqueous solubility. On the other hand, salts formed with alkaline earths or heavy metals exhibit limited or no solubility in water. B. 1 Acylated Amino Acids and Acyl Peptides These substances are usually prepared by the reaction of a natural amino acid or of a peptide with a long-chain fatty acid derivative. In this reaction, primary amino groups are converted into acylated amido groups. This destroys the zwitterionic character of the amino acid or of the peptide and increases the acidity of the carboxylic acids. After completion of the acylation, these acid groups are frequently neutralized with a suitable alkali. The following examples illustrate some of the structures: Collagen or some of its hydrolysis products are the most common sources of the protein. The level of hydrolysis (enzymatic or chemical) is not generally specified, and so-called acylated peptides are likely to contain considerable amounts of acylated amino acids. Since some of the amino acids contain more than one site for acylation (e.g., hydroxyproline), the end products are probably rather complex mixtures and may include some simple soaps. The acyl sarcosinates (derived from N-methyl glycine) occupy a special niche in cosmetics. These substances behave like soaps. The key to their performance and mildness is the fact that the carboxyl group has a lower pKa than that of typical fatty acids. The salts of the sarcosinates are water soluble and can be used at pH levels near or even slightly below neutrality. Acylated amino acids, depending on molecular weight and complexity, foam modestly and are generally viewed as exceptionally mild. They find use in skin and hair cleansing products and have been included in syndet bars. They reportedly exhibit substantivity to hair and skin proteins. Members of this class are sometimes identified as amphoteric. Under conditions of cosmetic usage (pH 4 to 9), acylated amino acids or peptides carry an anionic charge that is neutralized by a suitable cation. Their reported substantivity to hair
  • 36. or skin is the result of some unidentified proteinprotein interaction unrelated to the charge on the surfactant's head group. Acylated amino acids are amides and subject to chemical (or enzymatic) hydrolysis.
  • 37. Page 8 They are, however, stable at the pH commonly found in cosmetics but are subject to microbial attack. Preservation against spoilage remains a major problem, especially in the case of the peptide-derived products. B. 2 Carboxylic Acids (and Salts) B. 2. (a) Alkanoic Acids The most important members of this subgroup are the fatty acids derived from plant and animal glycerides. These natural acids normally possess an even number of carbon atoms and carry only one carboxylic acid group. The unsaturation in natural fatty acid is almost exclusively cis. A few natural fatty acids also contain a hydroxy group. In addition, some alkanoic acids are prepared synthetically, especially those in which the alkyl group is branched (iso). Fatty acids are obtained by the alkaline hydrolysis of fats and oils. Acidification after removal of unsaponifiables yields a water insoluble fatty acid blend named on the basis of its source, e.g., olive oil fatty acids. Specific fatty acids (e.g., oleic acid), can be isolated from these mixtures by various chemical and physical techniques. Alkanoic acids, as a group, are important industrial chemicals and are used in the synthesis of many types of substances. One of the most important modifications of alkanoic acids is reduction to fatty alcohols, which are then processed further to yield a variety of surfactants. Free alkanoic acids are of limited use in cosmetics, but the water soluble salts (soaps) are amongst the most useful surfactants known. Soaps have been utilized as cleansers and detersive agents since antiquity. In modern practice, soaps are the alkali or low molecular weight amine salts of alkanoic acids. Their water solubility depends on the pH of the system and on the cation. As a rule, potassium salts are more soluble than the sodium salts. The alkanoic acids are weak acids, with a reported pKa of about 56. Therefore soapsas salts of weak acidsyield alkaline aqueous solutions due to their dissociation in water. The solubility of alkali or amine salts of alkanoic acids in water decreases as the length of the alkyl chain increases. Thus, sodium stearate, especially in the presence of some free stearic acid, is insoluble enough to permit manufacture into soap bars. The alkaline earth and metal salts of alkanoic acids are water insoluble. Thus, calcium salts precipitate in aqueous systems leading to the formation of so-called soap scum. Alkanoic acid salts in which the alkyl chain contains about ten or fewer cations are not useful as surfactants, i.e., they do not foam well, have no detersive qualities, and are poor emulsifiers. The stearic acid of commerce contains about 45% of octadecanoic and 55% of hexadecanoic acids. The product may include small amounts of oleic acid and other acids normally found in the starting lipid. Modern grades of stearic acid are
  • 38. primarily prepared by hydrogenation of soybean fatty acids. For illustrative purpose, the following structures are included: Water soluble soaps are used as skin and hair cleansing agents, while the insoluble
  • 39. Page 9 derivatives (e.g., zinc laurate or magnesium stearate) are used for lubricating solids to improve flow properties, act as binders, and increase the viscosity of nonaqueous systems. Sodium stearate is soluble in warm ethanol and tends to gel upon cooling. Thus this substance has found extensive use in the formulation of alcohol-based stick deodorants. Water soluble and water insoluble soaps are good emulsifiers, the former primarily for o/w emulsions, while soaps such as aluminum stearate tend to form w/o emulsions. As a rule, oleic acid salts are especially useful emulsifiers, but their usage is restricted by the tendency of this unsaturated acid to form malodorous or discolored peroxidation products. One of the most important applications of soaps is represented by shaving soaps in general. Regardless of the method of shaving (brush, brushless, or aerosol), soap stocks from various sources are commonly blended to provide the shaver with copious and rapidly generated foam that lasts until shaving is completed. The topical use of soaps for skin cleansing is considered safe, although it has been shown that soaps can elicit adverse reactions on skin during closed patch testing [3]. B. 2. (b) Ester-functional Carboxylic Acids One type of ester-functional carboxylic acid is the small group of esters derived from polycarboxylic acids in which at least one of the carboxylate groups is free to form a salt. A typical example is stearyl citrate, the monoester of stearyl alcohol with citric acid. An entirely different type is represented by the acylation compounds of lactyl lactate. In their synthesis, two molecules of lactic acid are believed to react with each other, and the dimer then reacts with a fatty acid. The structure of a typical emulsifier created by this reaction is shown below: Compounds belonging to this class are safe for use in foods (baked goods), are occasionally used as cosmetic emulsifiers, and are reported to condition hair and skin. B. 2. (c) Ether-functional Carboxylic Acids Compounds belonging to the group of ether-functional carboxylic acids have recently gained some prominence in cosmetic usage. They may be viewed as alkylethers of polyethyleneglycol in which the terminal OH group has been oxidized to a carboxy group. The principal synthetic route depends on the alkylation (e.g., with chloroacetic acid) of an ethoxylated alcohol (D.3.a). As derivatives of glycolic acid, their pKa is quite low. The presence of the polymeric ether group increases the water solubility of these substances even if the starting alcoholic hydrophobe is relatively bulky. A typical structure is provided
  • 40. below for illustrative purposes: The water solubility of the free acids increases with increasing levels of ethoxylation. In this form, these compounds are useful as emulsifiers. Neutralization (usually with sodium ion) yields surfactants with detersive and solubilizing properties. These compounds are stable under normal conditions of cosmetic use. Compounds of this type have been shown to reduce the skin irritation potential of other anionic surfactants [4,5] and are generally milder themselves [6].
  • 41. Page 10 B. 3 Sulfonic Acid Derivatives The extremely stable CS bonds of these alkyl sulfonic acids distinguish them from compounds containing hydrolyzable COS bonds. The oxidative state of the sulfur atom also precludes most elimination reactions. Organic sulfonic acids are strong acids and in cosmetics are used only as salts. The sulfonates are generally divided into six subgroups. All sulfonates are chemically stable in cosmetics, and most are well tolerated on the skin. B. 3. (a) Taurates The taurates are a small group of compounds which are derived from taurine or N-methyl taurine by acylation. In aqueous solutions these amides are not stable and are subject to self-hydrolysis. Oh the other hand, they are stable in neutralized (generally sodium salt) form. A typical structure of a taurate follows: Taurates as a group foam well and have found usage in bubble baths and cosmetic skin and hair cleansing products. B. 3. (b) Isethionates Isethionates are the esters formed between isethionic acid (HOCH2CH2SO3H) and long- chain alkanoic acids. Like the taurates, the isethionic acid esters are strong acids and are subject to self-hydrolysis in aqueous systems. They are, therefore, useful in cosmetics primarily as sodium salts, as shown below: Isethionates are compatible with other anionic and nonionic surfactants. The limited number of cosmetically useful isethionates does not reflect their importance in liquid and solid skin cleansing products. Their irritation potential is considered to be very low, and they are important constituents of syndet bars. B. 3. (c) Alkylaryl Sulfonates Alkylaryl sulfonates are prepared by sulfonation of a number of alkyl substituted aromatic hydrocarbons. The starting hydrocarbon may be obtained by alkylation of benzene, naphthalene, toluene, or similar aromatic compounds. The alkyl s