SUN CARE 10% Lipophilic Phase ■ 30% Lipophilic Phase Extract ■ 100000 10000 10000 1000 100 10 1 10 Shear rate in 1/s
Figure 4: Shear test of P2P emulsions with different ratios of oil to water Note: A higher ratio of the lipophilic phase leads to an increase in viscosity
the emulsion is prepared. A good hint that this assumption might be correct came out of computer simulation experiments, which showed the formation of a classical emulsion by surfactant molecules under normal conditions.2 Unexpectedly, the formation of lamellar
structures was never obtained. This is because emulsion formation in a hot process always requires agitation. Thus, a shear-induced structure formation is almost unnoticeable. In aqueous media, lamellar structures of LCs
can be identified by optical microscopy. It reveals non-spherical oil droplets (Figure 3), which are deformed by shear forces and maintain their deformation over time, due to encapsulation in lamellar networks. This indicates the rigidity of the LC domains, which surround the oil droplets and delivers an explanation for the outstanding emulsion stability.
Rheological behaviour The rheological behaviour of an emulsion is an important characteristic of the appearance of personal care products. A shear test reveals the flow curve in the range of interest for personal care applications. As shown in Figure 4, a thin lotion with 10% lipophilic phase and a cream with 30% lipophilic phase both show a noticeable shear-thinning effect, which provides a pleasurable skin feel when applied. Shear-thinning is obtained as viscosity decreases with shear rate. An extrapolation to smaller shear rates leads
to an infinitely high viscosity which explains that these emulsions impart a gel-like flow behaviour. In addition, thixotropic behaviour, which means a thinning effect over time of flow, can be found for both emulsions. This flow behaviour underlines the lamellar structure-based emulsion model. To find the best balance between stability and amount of emulsifier is to consider the ratio between oil and water. The higher the amount of oil, the higher the suggested amount of emulsifier. Figure 5 shows the dependence of the viscosity on the ratio of lipophilic phase, which is gradually increased. This should give a practical guide as to
which concentrations are relevant to receive a thin lotion or a thick cream. A thin lotion with a concentration of 5% of the hydrophobic phase can be achieved as a stable emulsion system
www.personalcaremagazine.com 100 1000
> Shear thinning > Thixotropy (timewise thinning) > Gel-like flow behaviour
Thixotropic gel with shear thinning 100 0 5 0.75% P2P based on emulsion 10 15 20 25 Weight % of lipophilic phase
ratio between oil & water Note: Amount of emulsifier increased with increasing oil content
by the use of only 0.75% PCetP emulsifier . The amount needs to be increased to 4.5% to prepare a very thick cream with 30% oil.
Water resistance PCetP is well known as a key component for water-resistant sun care applications with outstanding benefits in terms of emulsion performance including the stabilisation of mineral UV-absorbers such as zinc oxide and titanium dioxide. The contribution of PCetP emulsifier to water resistance when applied on skin has been confirmed by the standard water-resistance test. The protective effect of test formulations
after bathing was proven by the Colipa 2005 test3
as an in vivo method, where the
performance of a PCetP emulsifier-based cream was compared to a standard cream, named P2. For this purpose, the prescribed standard P2 cream was modified. As an emulsifier system, glyceryl stearate
and stearic acid are used in the standard P2. In the modified P2 cream these two ingredients were exchanged by the same amount of
Phase INCI/Ingredients A Aqua
Sorbitol
Triethanolamine Lanolin
Theobroma Cacao Seed Butter
Glyceryl Strearate Stearic Acid
B
Potassium Cetyl Phosphate (and) Behenyl Alcohol Pair2Phase1 (Schill+Seilacher GmbH)
Octyl Dimethyl PABA
Benzophenone-3 C Preservatives
7.00 3.00
q.s.
Standard P2 Modified P2 77.5
77.5
5.00 1.00 4.50
2.00 3.00
2.00 5.00
7.00 3.00
q.s.
Figure 6: Formula of standard P2 cream according to Colipa 2005 water resistance test & modified P2 cream including P2P emulsifier system
5.00 1.00 4.50
2.00
PCetP emulsifier, as shown in Figure 6. The test was carried out by an accredited institute. The result of this study is water resistance in percent, which relates the measured SPF before and after water immersion. To show that the test procedure is valid,
the Standard P2 cream needs to give a value of higher than 50%, which indicates a water- resistant formulation. Even the accredited laboratory reached with the standard P2 cream a value of 60.6%, the modified P2 cream achieved a significantly higher value of 74.7%. This outstanding result means that this is an easy approach to developing formulations with remarkably improved water resistance.
Conclusion PCetP supports O/W emulsification, especially in the presence of long fatty alcohols. Pair2Phase1 is a synergistic combination of PCP and behenyl alcohol which supports the robustness of creams and lotions. It is COSMOS- and NaTrue-approved, allows the formulation of water-resistant sun care products, provides a pleasant skin sensation without stickiness and also stabilises UV absorbers, including zinc oxide and titanium dioxide. Due to its driving force to form lamellar
surfactant phases it takes care to regulate humidity of the skin. The formation of liquid crystals can also be used as a prospective delivery system for cutaneous applications. All these sophisticated benefits are a result of the existence of extraordinary microstructures.
30 4.5% P2P based on emulsion Figure 5: Viscosity of emulsions at shear rates of 5/s depending on the 35
Lipophilic phase: 85% Sunflower oil 15% P2P Emulsifier
1000
Lipophilic phase: 85% Sunflower oil 15% P2P emulsifier Emulsifier
P2P ■ Sunflower oil ■ water■
95
PC
References 1. Davies, JT. A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent Gas/Liquid and Liquid/Liquid Interface (Proceedings of the International Congress of Surface Activity), 1957, 426–38
2. Klein, K. Liquid Crystals and Emulsions: A Wonderful Marriage. Cosmet. Toiletries, 2002. 117; 30-34
3. Cosmetics Europe: Guidelines for evaluating sun product water resistance: https://www.
cosmeticseurope.eu/files/7914/6407/7400/ Guidelines_for_Evaluating_Sun_Product_ Water_Resistance_-_2005.pdf
November 2021 PERSONAL CARE
Viscosity in mPas
Viscosity in mPas at Shear Rates 5/s
lotion
Cream
thick Cream
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104
