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The University of New South Wales School of Material Science and Engineering Physical Performance Properties and Morphological Characteristics of Dibenzylidene Sorbitol-solidified Propylene Glycol-Glycerin Matrices containing Mild Surfactants for Personal Cleansing A Thesis By Danilo L. Lambino Submitted in the Fulfillment of the Requirements of the Degree of Master of Science (MSc) August 2002 11 CERTIFICATE OF ORIGINALITY I hereby declare that this submission is my own work and that to the best of my knowledge and belief, it contains no material previously published or written by another person, nor material which to a substantial extent has been accepted for the award of any degree or diploma at UNSW or any other institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. Ill ACKNOWLEDGEMENTS I gratefully acknowledge Johnson & Johnson for funding this research and the many people who contributed to this study. I would especially like to thank: Dr. Sri Bandyopadhyay, my graduate supervisor for his guidance, support and encouragement. Dr. Aibing Yu, my graduate co-supervisor for his support and technical advice. Mr. Noble Mathew, my industry supervisor, for his commitment and passion for this research study. Mr. Gary Gao of UNSW and Dr. Susan Niemiec of Johnson & Johnson Topical Formulations and Drug Delivery Research Center for her technical support on the Freeze Fracture Transmission Electron Microscopy. Ms. Bettina Wolpensinger, Ms. Katie Levick, and Ms. Margaret Budanovic of the UNSW Electron Microscopy Unit for their technical assistance. Finally, and most important, rry mother Ligaya and sisters Lala and Lyn for being an enduring source of strength, inspiration and unfailing support. IV ABSTRACT Dibenzylidene sorbitol (DBS), a low molar mass butterfly-shaped amphiphile, is an effective solid gelator for organic liquids and polymeric melts. It can strongly interact through hydrogen bonding and self-associate into a three-dimensional nanofibrillar network. DBS finds practical applications in commercially important polyolefins such as polyethylene, which are primary components for packaging and construction materials. It acts as a nucleating agent in the formation of spherulites improving the polymer's optical clarity, yield and tensile strength. In personal care products, DBS is used as a solidifying agent for transparent antiperspirant and deodorant sticks. In this study, we have investigated the use of DBS in solidifying mild surfactant systems mixed with polar organic solvents glycerin and propylene glycol. These solid matrices can be used as milder cleansing alternatives to bar soaps, which are harsh on skin. The physical performance properties of the DBS-solidified matrices were defined through predictive model equations and then optimized using the principles and techniques of Mixture Design Experiments (MOE). The resultant optimised matrices have better bar wear rate and bar mush with comparable transparency to commercially available transparent soaps like Johnson's Baby Clear Soap. Also, given the V technology limitations the cleansing bar matrix was shown to have acceptable hardness and level of foaming. However, the major drawback is the matrix' susceptibility to syneresis when exposed to high humidity due to the presence of high concentrations of propylene glycol and glycerin in the formula. It was found 1hat addition of free water reduces syneresis but also reduces rigidity and clarity of the matrix. This study also investigated the morphology of DBS in the matrix via Atomic Force Microscopy and Freeze Fracture Transmission Microscopy. Topographic images show distinct formation of long nanofibrils and fibrillar bundles of DBS with each fiber cross-section measuring about 40nm. The twisting, interconnection and multidirectional percolation network of DBS fibers provided rigidity to the matrix. Introducing free water into the system results to a remarkable change in DBS morphology with thinner fiber cross-sections and absence of crosslinking, consistent with the loss of structure of the matrix. VI TABLE OF CONTENTS SECTION PAGE Certificate of Originality 11 Acknowledgement lll Abstract IV Table of Contents VI List of Figures Xl List of Tables XVI List of Equations XVlll List of Appendices XIX I INTRODUCTION II LITERATURE REVIEW 5 2.1 Dibenzylidene Sorbitol 5 2.1.1 Chemistry, synthesis and manufacture 5 2.1.2 Physico-chemical properties 9 2.1.3 Solubility 10 2.1.4 Morphological behaviour in various systems - DBS and its derivatives 13 2.1.5 DBS application in personal care formulations 24 2.2 Non-dibenzylidene sorbitol solid gel formers 27 2.2.1 Soap 27 2.2.2 Gelatin 30 2.2.3 Fatty alcohols and waxes 32 2.3 Advantages of DBS 35 2.3.1 Stability and compatibility 35 VII SECTION PAGE 2.3.2 Safety and toxicology 35 2.3.3 Transparency of solidified matrix 35 2.4 Disadvantages of DBS 37 2.4.1 Insolubility in water 37 2.4.2 High temperature dissolution 37 2.5 Commercially available cleansing bar matrices 38 2.5.1 Opaque sodium soap bar 38 2.5.2 Translucent or pearlized soap bar 41 2.5.3 Transparent soap bar 41 2.5.4 Syndet bar 42 III SCOPE OF PRESENT WORK 48 IV MATERIALS, METHODS AND DESIGN 49 4.1 Raw Materials 4.1.1 Polar Solvents 49 4.1.2 Surfactants 52 4.1.2.1 Anionic surfactants 52 4.1.2.2 Nonionic surfactants 54 VIII SECTION PAGE 4.1.2.3 Amphoteric surfactants 54 4.1.3 Gelling synergist 56 4.1.4 Chelating agent 57 4.2 Test Methods for Physical Performance Properties 58 4.2.1 Bar penetration 58 4.2.2 Bar mush 61 4.2.3 Foam volume tumbling tube 63 4 .2.4 Bar wear 65 4.2.5 Syneresis 67 4.2.6 Transparency 69 4.3 Test Methods for Morphological Characterization 72 4.3.1 Atomic force microscopy 72 4.3.2 Freeze fracture transmission electron microscopy 76 4.4 Experimental Procedure 78 4. 4 .1 Objectives of the experiment 79 4.4.2 Identification of critical cleansing bar properties 80 4.4.3 Identification of ingredient range cf concentrations 82 4.4.4 Selection of mixture design 85 4.4.5 Experimentation and preparation of product formulations 87 IX SECTION PAGE V RESULTS AND DISCUSSION 91 5.1 Mixture Design Analysis 91 5.1.1 Model Equation Selection 94 5.1.1.1 Model Fit 94 5.1.1.2 Analysis of Variance 97 5.1.1.3 Diagnostics - Bar wear example 98 5.1.1.3.1 Normal Plot 99 5.1.1.3.2 Residual versus predictive plot 99 5.1.1.3.3 Residual versus run 100 5 .1.1. 3 .4 Residual versus factor 101 5.1.1.3.5 Outliers 101 5.1.1.3.6 Cooks distance 102 5 .1.1. 3. 7 Leverage 102 5.1.1.3.8 Predicted versus actual plot 103 5.1.1.3.9 Box-Cox plot 103 5.2 Predictive Model Equations and Graphs 104 5.2.1 Bar hardness 107 5 .2.2 Bar mush 108 5.2.3 Bar wear 109 5.2.4 Foam volume 110 X SECTION PAGE 5.2.5 Transparency 112 5.2.6 Syneresis 113 5.2.6.1 Effect of equilibrium moisture concentration 114 5.2.6.2 Effect of hydroxypropyl cellulose in competitive hydroge1r 125 bonding 5 .2.6.3 Effect of higher DBS concentration 126 5.3 Mixture Optimization 129 5.4 Morphological Characterization 137 5.4.1 Surface topography analysis 138 5.4.2 Effect of HPC on the morphology of DBS in the matrix 144 5.4.3 Effect of free moisture on the morphology of DBS in the matrix 147 5.4.4 Morphology of soap bar matrices 150 5.4.5 Freeze fracture transmission microscopy 152 5.4.5.1 DBS and HPC in surfactant matrices 153 5.4.5.2Clear and opaque soap structures 157 VI CONCLUSION 160 VII RECOMMENDATIONS FOR FURTHER WORK 162 VIII LIST OF REFERENCES 164 Xl LIST OF FIGURES Figure Title Page Antiperspirant and deodorant stick products 3 2 DBS molecule 5 3 DBS synthesis 6 4 Process flowchart for Disorbene LC manufacture 8 5 Polarized light microscopy image of DBS particles 9 6 Dissolution profile of DBS in various solvents 11 7 SEM micrographs of DBS network in PDMS 14 8a Scanning electron micrographs of DBS network at 15 high magnification 8b Scanning electron micrographs of DBS network at low 16 magnification 9 Polarized light micrographs of DBS network revealing 17 a highly ordered structure of birefringent spherulites 10 Dynamic viscoelastic moduli shown as a function of 18 strain (Y) for a 1% DBS gel 11 Electron Micrographs of D-DBS in solvents with 19 different donor number 12 Morphological investigation via TEM of crystalline DBS 21 with PPO and PP 13 TEM images of DBS in PPO12 gel matrix at two 22 different magnification XII Figure Title Page 14 Soap processing routes 28 15a Gelatin's amino acid composition 30 15b Gelatin's structural chain 31 16 Transparency of gelled solvent versus DBS concentration 36 17 Soap processing and finishing process 39 18 Soap finishing line (Mazzoni LB) 40 19 Chemical structure of glycerin and propylene glycol 51 20 General chemical structure of anionic surfactants 53 21 Chemical structure of anionic surfactants used 53 22 Class chemical structure of sorbitan ester 54 23 Chemical structure of amphoteric surfactants used 55 24 Idealized structure of HPC, molar substitution= 3.0 56 25 Disodium EDTA chemical structure 57 26 Penetrometer equipment-product set-up 59 27 Soap mush test procedure 62 28 Foam volume tumbling tube equipment 65 29 Humidity chamber 68 30 Basic AFM set-up 73 31a AFM Equipment set-up 73 31b Basic scanning probe microscopy components