Stabilisation of water-in-oil emulsions to improve - eTheses ...

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(a) (b) (c) Fig. 2.8. Triple chain length structures, (a) alpha (α) tuning fork, (b) beta prime (β’) tilted tuning fork and (c) beta (β) stacked chair. (Adapted: Culot et al., (1994)) Long spacing Garti, Binyamin and Aserin (1998) have demonstrated that it is possible to stabilise W/O emulsions by α-form polymorphs in conjunction with polyglycerol polyricinoleate (PGPR) which is used as a non ionic lipophilic emulsifier. However in order to achieve a large amount of α-form polymorphs in the continuous phase, flash cooling of the triglycerides (tristearin) was required prior to emulsification. These emulsions were not stable, however, for sufficiently long periods. Applying the hypothesis could be useful in producing water-in-oil cosmetics like lipstick. However as stated crystalline polymorphs transitions over time could result in undesirable and unstable products. This dilemma of polymorphic changes occurring during storage could be 31 Long spacing Long spacing
prevented by the addition of crystal modifying emulsifying agents according to research conducted by Krog (1977) where sorbitan esters were used to stabilize the intermediate beta prime (β’) crystal form. Whilst fat crystallisation can help to stabilise W/O emulsions, fat crystallisation within O/W emulsions has a tendency to reduce emulsion stability, causing partial coalescence. This is due to the crystals (those that are rigid enough to overcome the Laplace pressure) penetrating the interfacial layer between the two droplets. This produces a bridge which in turn leads to coalescence between the two drops. Whilst crystal penetration (leading to partial coalescence) of oil droplets in typical oil-in- water emulsions may be undesirable, fat crystallisation is important in supporting the structure of the air cells in typical foams like ice cream and whipped cream (Coupland, 2002). Penetration of the interfacial layer is less likely if the crystals are able to conform to the shape of the droplet. As mentioned earlier alpha (α) polymorphs have a more liquid malleable character and are therefore more likely to follow the contours of the droplets. Also fats containing a broad mixture of triglycerides will tend to form a mixed crystalline structure, giving rise to a softer mechanical structure hence a more stable emulsion. Other factors such as interfacial film thickness along with environmental factors have been found to affect whether or not the crystals are able to penetrate and hence destabilize an emulsion; of course interfacial film thickness is dependent on the choice and quantity of emulsifier used. Protein stabilised emulsions have been found to be more stable than small-molecule surfactants due to the formation of a thicker interface (Darling and Birkett, 1987). Whilst crystallisation may be required to stabilise W/O emulsions, which appropriately would be the case in stabilising W/O cosmetics, this could lead to an increase in the hardness of the final emulsion. Although this is important, in 32
Page 1 and 2: Stabilisation of water-in-oil emuls
Page 3 and 4: Abstract The stabilisation of water
Page 5 and 6: Contents 1 Introduction ...........
Page 7 and 8: 4.7.1 Penetrometer Test ...........
Page 9 and 10: Figures Fig. 1.1. The global cosmet
Page 11 and 12: Fig. 5.18. DSC Thermograms for the
Page 13 and 14: Fig. 5.36. Changes in the viscoelas
Page 15 and 16: Table. 5.6. Emulsion based Lipstick
Page 17 and 18: Symbols α Alpha β Beta β’ Beta
Page 19 and 20: provide additional moisture for the
Page 21 and 22: 1.1 Layout of the Thesis This Thesi
Page 23 and 24: more than 2 to 3 applications daily
Page 25 and 26: O HO O C H 3 CH 3 O OH O O O Molecu
Page 27 and 28: C H 3 HO O OH Molecular Formula = C
Page 29 and 30: C H 3 C H 3 Molecular Formula = C 6
Page 31 and 32: the long chains. Due to its structu
Page 33 and 34: and subsequent infections. This can
Page 35 and 36: In order to attain a state of minim
Page 37 and 38: which there is an excess of opposit
Page 39 and 40: By applying the HLB system, one wil
Page 41 and 42: 2.7 Emulsion stability & instabilit
Page 43 and 44: (Voorhees, 1992; Dickinson, Ritzoul
Page 45 and 46: chains are in free rotation and pre
Page 47: (a) (b) (c) Fig. 2.7. Double chain
Page 51 and 52: 2.9 Microbial stability & Origin of
Page 53 and 54: There are a number of important fac
Page 55 and 56: which of course is an important con
Page 57 and 58: ideal for assessing not only the de
Page 59 and 60: 3 Materials 3.1 Waxes & Emulsifiers
Page 61 and 62: With the continuous phase being oil
Page 63 and 64: melting point range in order to mai
Page 65 and 66: The moulds were then placed in a fr
Page 67 and 68: Table. 4.2. IFT Procedure settings
Page 69 and 70: 4.4 Emulsion Lipstick Preparation F
Page 71 and 72: The water was transferred directly
Page 73 and 74: emulsions were taken in triplicate
Page 75 and 76: d0,0; number-weighted mean (e.g. NM
Page 77 and 78: 4.7 Texture Profile Analysis - TA T
Page 79 and 80: 4.7.2 Compression Test The second m
Page 81 and 82: 4.7.3 Rheology Rheological non-dest
Page 83 and 84: critical micelle concentration (CMC
Page 85 and 86: Interfacial Tension (mN/m) 10 CMC -
Page 87 and 88: Sorbitan Hydrophilic portion (Water
Page 89 and 90: HO O O O O Water droplet O O O O HO
Page 91 and 92: 5.3.2 Wax selection for Simplified
Page 93 and 94: 5.3.3 Thermo-physical Characteristi
Page 95 and 96: Heat Flow Endo/Exo (mW) 2% PGPR DSC
Page 97 and 98: Heat Flow Endo/Exo (mW) 2% Span 80
Page 99 and 100:
Table. 5.3. Thermo-physical charact
Page 101 and 102:
Relative frequency Emulsion Stabili
Page 103 and 104:
drainage and rupture. In spite of t
Page 105 and 106:
Table. 5.4. Emulsion based Lipstick
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
the emulsification process along wi
Page 113 and 114:
Fig. 5.29. 30 wt% water content wit
Page 115 and 116:
Fig. 5.33. Cryo-SEM micrograph of H
Page 117 and 118:
no doubt give rise to a much denser
Page 119 and 120:
Table. 5.9. Texture profile penetro
Page 121 and 122:
Table. 5.10. Compression firmness d
Page 123 and 124:
Although no emulsions were prepared
Page 125 and 126:
G' & G'' (Pa) x 10 5 Viscoelastic p
Page 127 and 128:
Table. 5.11. Viscoelastic moduli, G
Page 129 and 130:
potentially reduce microbial spoila
Page 131 and 132:
Appendix The following Figures; 5.9
Page 133 and 134:
Heat Flow Endo/Exo (mW) 5 4 3 2 1 0
Page 135 and 136:
Heat Flow Endo/Exo (mW) 2.0 1.5 1.0
Page 137 and 138:
References Adamczyk, S., Lázaro, R
Page 139 and 140:
Dweck, A. C., & Burnham, C. A. M. (
Page 141 and 142:
Kobayashi, H., & Tagami, H. (2004).
Page 143 and 144:
Pourreza, N., & Rastegarzadeh, S. (
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