IFSCC MONOGRAPH Number 3 An Introduction to Rheology ~~»4ATIONAL FEDER'l>/o~ ts,· (f 360/ET/ES OF CC)shicric j IFSCC MONOGRAPH Number 3 An Introduction to Rheology Published on behalf of the International Federation of Societies of Cosmetic Chemists by ~~ MICELLE PRESS ~ Weymouth, Dorset, England Copyright© 1997 by the International Federation ofthe Societies of Cosmetic Chemists Originally published 1997. This booklet first issued in a Print-on-Demand edition in 2011. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the International Federation of the Societies of Cosmetic Chemists. A catalogue record for this book is available from the British Library ISBN: 978-1-870228-16-9 Published by Micelle Press 12 Ullswater Crescent, Weymouth, Dorset DT3 5HE, England http://www. micellepress.co.uk E-mail: [email protected] and RO. Box 1519, Port Washington, NY 11050-7519, USA http:/Mww.scholium.com E-mail: [email protected] on behalf of the International Federation of the Societies of Cosmetic Chemists IFSCC Secretariat Suite 6, Langham House East, Mill Street, Luton, Beds LU 1 2NA, England http://www. ifscc. org E-mail: enquiries@ifscc. org Printed and bound in Great Britain by CPI Antony Rowe, Eastbourne IFSCC Benefactors The current list of benefactors, to whom we offer our profound thanks for their continuing support ofthe IFSCC, are shown below: Amore Pacific Corporation Iwase Cosfa Company Ltd. [Koreal [Japan] BASF [Germany] Kanebo Cosmetics Inc. [Japan] Bioland Ltd. [Korea] Kose Corporation [Japan] COESAM [Chile] Lipo Chemicals Inc. [USA] COGNIS Care Chemicals Matsumoto Trading Co. Ltd [Germany] [Japan] Cosmetics & Toiletries [USA] Nalco Company [USA] CRB [Switzerland] Nikko Chemical Company [USA] 1 Croda, Inc [USA] Plantapharm Chem [Austria] DROM [Germany] Pola Chemical Industries Inc. DSM [Switzerland] [Japan] Evonik Goldschmidt [Germany] Provital SA [Spain] Firmenich SA [Switzerland] Shiseido Co. Ltd [Japan] Greentech [France] Silab [Francel Ichimaru Pharcos Co. Ltd Symrise Inc. [USA] [Japan] T. Hasegawa Co. Ltd. [Japan] 'Induchem Ltd [Switzerland] Takasago Inc. Corp. [Japan] Interlees Corporation [Koreal Toyo Beauty Co. Ltd [Japan] ISP Europe [UK] Unilever [USA] The following companies also make a substantial contribution to the IFSCC in supporting members of the Praesidium, and our grateful thanks also go to: Amore Pacific Corporation Mae Fah Luang University [Korea] [Thailand] Australian Photobiology Testing Nordbak [South Africa] Facility [Australia] Pertech Associates [UK] Beiersdorf AG [Germany] Shiseido Co. Ltd [Japan-] Chanel, Inc. [USA] Symrise [Spain] Gigot Cosmetics [Argentina] Tri-K Industries [USA] JW Solutions [The Netherlands] General Preface to the Series There are many excellent, authoritative textbooks covering the differ- ent areas which comprise Cosmetic Science. However, certain topics cut across these various disciplines and are best studied individually. From the study of such a topic, a better appreciation can be achieved of the practical use of that topic in the cosmetic field. This series of IFSCC monographs is a collection of such intersecting themes. It is hoped that the knowledge gained from identifying activities common to a number of areas will be transferable when a chemist moves from project to project. This series of monographs will cover a wide range of themes compiled by experts in their fields, providing both the novice and the experienced individual with valuable reference books on the major topics of Cosmetic Science. Monographs already published in this series are IFSCC Monograph No. 1 : Principles of Product Evaluation: Objective Sensory Methods IFSCC Monograph No. 2 : The Fundamentals ofStability Testing IFSCC Monograph No. 3 : An Introduction to Rheology IFSCC Monograph No . 4 : Introduction to Cosmetic Emulsions IFSCC Monograph No . 5 : An Introduction to Cosmetics Micro-. biology IFSCC Monograph No. 6 : Antiperspirants and Deodorants: Principles of Underarm Technology IFSCC Monograph No. 7 : Microemulsions in Cosmetics In a further series, the IFSCC has also published Cosmetic Raw Material Analysis and Quality: Hydrocarbons, Glycerides, Waxes and Other Esters, edited by Hilda Butler Cosmetic Raw Material Analysis and Quality: Analysis of Polymers for Cosmetics, by Janusz Jachowicz Foreword The application of rheology in many different industries has been stead- ily increasing. Terms which were once reserved for only the nnost ab- stract articles are now creeping into our common vocabulary. The IFSCC has recognized the need for a practical review of this discipline with cosmetic rheology in mind. It is hoped that by promoting a more widespread understanding of the underlying principles of rheology, cos- metic science itself may be advanced. This monograph has been written and published with that in mind. The IFSCC is grateful to Dennis Laba for preparing this monograph on rheology. Contents Page IFSCC Benefactors General Preface to the Series iv Foreword 1 Introduction to Rheology 1 Cosmetic rheology 1 Definitions 3 Types of flow 7 2 Using Cosmetic Rheology 13 , Formulating with rheology in mind 13 Rheology as a manufacturing tool 15 Rheological principles in stability testing 17 Predicting consumer acceptance 18 3 Rheological Additives 22 4 Instrumentation 27 5 Interpreting Rheological Profiles 31 6 Suggested Reading 35 Introduction to Rheology 1 1 Introduction to Rheology Cosmetic rheology Rheology is the science or study of flow. Cosmetic rheology, therefore, involves the characterization or measurement of flow that takes place in cosmetic products. To the average consumer, proper cosmetic flow may hardly be noticeable. That same consumer, though, is likely to be acute- ly aware of the lack of an expected kind of flow. If a hand lotion does not easily flow from the bottle, something is wrong; if a lipstick does not transfer smoothly to the lips, something is wrong; if a shampoo doesn't have enough body momentarily to be held neatly in your hand, something is wrong. That 'something' is the product's rheology. During the course of product development, the cosmetic scientist must design key rheological characteristics into the product. Formu- lators must take into account the variable desired flow characteristics during processing, packaging, transport, storage, and consumer use. Developmental scientists have a responsibility to their profession, to their company, and to the consumer to ensure that the cosmetic can be reproducibly manufactured and will remain stable and usable through- out the life of the product. Of course, the cosmetic scientist is not alone in this challenge; many other industries take rheology very seriously. The paint and coatings industry, for example, is acutely aware of the required rheological characteristics of their products. Nail polish scien- tists share many of the same requirements, since they are also in the 'coatings' area. The formulators come face to face with rheological challenges while the product is waiting to be used, while it is being transferred from bottle to nail, and finally during application. Initially, the formulator must make sure that the pigments stay in suspension as long as possible to present a uniform color and appearance to the con- sumer. The product must then be 'picked up' appropriately by the brush, and stay neatly on the applicator while it travels through the air without dripping. Application properties are then held in delicate balance with the leveling properties. On the one hand, formulators must prepare a product that is apparently thick enough not to drip or run off the nail when applied, yet is thin enough to allow the brush marks to flow together, presenting a smooth, uniform surface before the film dries. All these interconnected properties are carefully balanced in the search for the perfect nail enamel system. 2 IFSCC Monograph No. 3 While it is true that each cosmetic product category is unique, many share common rheological concerns. Table 1 Rheological concerns in cosmetic products Cosmetic product Rheological concerns Lipstick Suspension of pigments in molten state Thermal stability during storage Even flow or payout onto the lips Mascaras Suspension of pigments Spreadability Proper viscosity for use Emulsion stability Shampoo Proper viscosity Proper flow characteristics Actives suspension in therapeutic formulas Nail enamel Suspension of pigments Proper flow and leveling Proper viscosity Creams/Lotions Proper 'body' or viscosity Emulsion stability Spreadability Extrudability Antiperspirants Suspension of the actives Flow control of the roll-on formula Thickening Spreadability Payout of the stick formula Though pigments in lipstick are certainly different from the active ingredients used in antiperspirants, both are solids that need to be held in uniform suspension. The cosmetic scientist must look beyond the ob- vious differences and deal with the underlying rheological need. For- tunately, scientists now have many tools available to help them form- ulate products with the needed rheological characteristics. An arsenal of additives has been developed to provide specific properties for either Introduction to Rheology 3 water or oil systems. Some of the additives are as seemingly simple as clays, while others are complex reaction products of multiple raw materials. To keep watch over the effects of