Shear-Thinning Lamellar Gel Network Emulsions as Delivery Systems

26 Shear-Thinning Lamellar Gel Network Emulsions as Delivery Systems Irma Ryklin and Blaine Byers Stepan Company Northfield, Illinois

26.1 26.2 26.3 26.4

Introduction ................................................................................... 548 The “Eureka!” Effect ..................................................................... 548 Preparation of Lamellar Gel Network Emulsions .......................... 549 Molecular Identification.................................................................. 550 26.4.1 Chemistry and Function.................................................... 550 26.4.2 Molecular Modeling of Sodium Stearyl Phthalamate ......... 550 26.4.3 Interfacial Tension (IFT) .................................................... 552 26.5 Identification and Characterization of Lamellar Gel Network Structure ......................................................................... 552 26.5.1 Conductivity Method .......................................................... 552 26.5.2 Rheological Method .......................................................... 554 26.6 Applications .................................................................................. 554 26.6.1 Skin Irritation ..................................................................... 554 26.6.2 Moisturization Effect of RM1 in Creams and Lotions ........ 556 26.6.3 SPF Enhancement in Sunscreen Formulations ............... 559 26.6.4 Formulating Sprayable Products ...................................... 564 26.7 Conclusion .................................................................................... 564 26.8 Formulations ................................................................................. 565 References .......................................................................................... 568 Acknowledgment ..................................................................................... 568

Meyer R. Rosen (ed.), Delivery System Handbook for Personal Care and Cosmetic Products, 547–568 © 2005 William Andrew, Inc.

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26.1 Introduction The majority of current products in the skin and sun care market are formulated emulsions. These products are designed to have the appearance and flow behavior of lotions or creams. As skin care products become more sophisticated with the incorporation of new arrays of active ingredients, their optimal delivery of these active ingredients becomes increasingly important. To this day, such emulsions continue to be the most popular vehicle for delivering functional cosmetic ingredients to the skin. In recent years there has been an increasing interest in “multiple-phase,” oil-in-water emulsions. Such systems should not be confused with “multiple emulsions,” which may be considered ordinary twophase emulsions in which droplets of the dispersed phase contain even smaller-sized droplets that are miscible with the external or continuous phase.[1] “Multiple emulsions” can be a water-in-oil-in-water type where internal and external phases are separated by an oil phase or an oil-in-water-in-oil type, where the two oil phases are separated by a water phase. The modern multiple-phase emulsions are not simple mixtures of oil, water, and emulsifiers, but are more complex systems. [2][3] They are polydispersed systems that contain several surfactant and amphiphilic emulsifiers and not only usual phases of water and oil, but additional phases as well. The additional phases generally form in aqueous media when an emulsifier, in excess of amount required to form a monomolecular layer at the oil-water interface, interacts with a continuous water phase and are called lamellar phases. In lamellar phases, surfactant molecules are arranged in bilayers separated by layers of water (Fig. 26.1). The carbon chains of the bilayers can exist in a number of physical states such as ordered, or gel, and disordered, liquid crystalline. In gel state, the hydrocarbon chains are packed in a hexagonal subcell with rotational motion about the long axes, whereas in the liquid crystalline state, they are disordered and liquid-like. The order-disorder transition, Tc , is the melting point of the carbon chains. When chains melt, the lamellar arrangement of bilayers still persists due to the strong forces linking the polar groups together. The melting and transition occurs at a characteristic temperature, influenced primarily by the hydropho-

Figure 26.1 Schematic diagram of an emulsion droplet stabilized by multilayers of lamellar liquid crystals.

bic part of the surfactant. The liquid crystalline gel transition temperatures of many amphiphile/surfactant combinations are above ambient, so that crystalline phases occur only at the high temperatures during preparation; upon cooling, gel phases form. The presence of additional lamellar phases, either crystalline or gel, responsible for creating a structuring effect in the emulsions is known to be a key to improved stability, desired rheological profile, and improved active delivery properties.[4][5] Selection of the emulsifier system is one of the most important aspects of formulating effective multiple-phase emulsions useful as delivery system vehicles. The emulsifier system is responsible for providing the desired structuring effect and should be carefully selected to maximize the emulsions delivery properties, as well as being nonirritating and safe.

26.2 The “Eureka!” Effect In light of the cosmetic industry’s need for emulsification systems that allow one to produce modern structured cosmetic creams and lotions, it was very exciting for our company when we discovered a technology which utilizes a non-conventional anionic rheology-modifier/emulsion-stabilizer capable of forming lamellar or crystalline structuring in multiple phase emulsions. This key ingredient was sodium stearyl phthalamate (STEPAN-MILD® RM1).

RYKLIN AND BYERS: SHEAR-THINNING LAMELLAR GEL NETWORK EMULSIONS AS DELIVERY SYSTEMS The initial discovery of elegant emulsions that exhibited outstanding rub-in and skin feel led us to explore and fully develop what turned out to be a non-conventional emulsifying system. In contrast to conventional emulsifying systems that required different emulsifiers for oils with different “required” hydrophilic-lipophilic balance (HLB) values, our nonconventional system appeared to be independent of HLB! It was equally capable of emulsifying a full range of oils with required HLB ranging from 5 to 12. Surprisingly, and unexpectedly, it was also observed that the concentration of emulsifier system did not have to be varied since it could easily emulsify low-oil volume fraction as well as high-oil volume fraction emulsions. Results of further developmental work and a number of applied experimental techniques allowed us to establish that when our non-conventional emulsifier, sodium stearyl phthalamate, is combined with a low-HLB emulsifier and a polymeric emulsifier, it is capable of producing multiple-phase, oil-in-water emulsions that have a lamellar gel network structure. The formed structure provides a unique combination of benefits. These include a stabilizing mechanism that enhances the product’s stability and an extremely favorable rheological profile that provides unique sensory and performance characteristics to cream and lotion products. Another benefit of the technology is the strong moisturizing effect on the skin. This is attributed to the compatibility of the resulting lamellar gel structure with the natural lamellar structure of the stratum corneum lipids. Further, we also observed a significant SPF enhancement in sunscreen formulations using the technology and, since the emulsifying system is water-insoluble at room temperature, emulsions based on it are inherently mild.

26.3 Preparation of Lamellar Gel Network Emulsions The technology enables the preparation of oilin-water emulsions with a pH level above 6.5. A typical emulsion system is composed of three ingredients with sodium stearyl phthalamate as a key component that functions both as a rheology modifier

549

and as an emulsion stabilizer. The recommended sodium stearyl phthalamate concentration is from 1.0% to 1.5% and is employed in conjunction with a low-HLB emulsifier (such as glyceryl stearate) in a 2:1 ratio. An anionic polymeric emulsifier, such as pemulen (acrylates/C 10-30 alkyl/acrylate crosspolymer), is also included in an approximately 5:1 ratio (sodium stearyl phthalamate to polymeric emulsifier). The emulsification system is highly cost effective because the total amount of all components ranges from 1.7% to 2.5%. Emulsions made with this technology are extremely versatile since it is capable of producing stable emulsions with various oils and active ingredients, over a wide range of HLB values and a broad range of oil concentrations (5% to 45%). A standard method of emulsion preparation includes the following steps: • The polymeric emulsifier is added to the aqueous phase, and neutralized to a pH of 7.0–7.4 prior to the addition of sodium stearyl phthalamate. Addition of the neutralizing agent after combining aqueous and oil phases at high temperature is possible, but not preferred. • Sodium stearyl phthalamate is added to the aqueous phase of the emulsion at 72°C– 75°C, with moderate agitation, and mixed for at least fifteen minutes. This procedure allows the material to dissolve and form a lamellar liquid crystalline phase. • A low-HLB emulsifier is added to the oil, which is kept separately at this point in the process. • The emulsification is then carried out at a temperature of 72°C–75°C by adding the oil phase to the water phase and mixing for at least 25–30 minutes. • pH modifiers, preservatives, and other temperature sensitive substances are added at temperatures below 40°C. • Homogenization at high temperature is not required, but can be applied at a temperature lower than 35°C, if desired. • Equilibrate the emulsion overnight prior to evaluation.

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26.4 Molecular Identification 26.4.1 Chemistry and Function The sodium stearyl phthalamate was prepared according to the procedure described in patent WO 91/01970[6] and is a free-flowing white powder at 98% solids. The chemical structure of STEPANMILD® RM1, the key component of the emulsification technology, is represented in Fig. 26.2. Sodium stearyl phthalamate is insoluble in water at room temperature, but becomes water-soluble at high temperature. As such, it interacts at the oil/ water interface, displaying interfacial tension reduction properties at elevated temperatures.

Figure 26.2 Chemical structure of sodium stearyl phthalamate.

26.4.2

Molecular Modeling of Sodium Stearyl Phthalamate

In order to better understand the unique properties that sodium stearyl phthalamate (STEPANMILD® RM1) exhibited, two molecular modeling studies were conducted. In the first one, the structural features were examined. Semi-empirical molecular modeling, Fig. 26.3, shows two hydrophilic and two hydrophobic areas in the molecule. The anionic carboxylate head group is cross planar to the hydrophobic aromatic ring (torsional angle of 75°) and positioned orthogonal to the amide hydrophile. The amide hydrophile is also cross planar to the aromatic ring with a torsional angle of 40.5°. In addition, the oxygen atom of the amide linkage is pushed away from the ortho carboxylate oxygens, thereby providing hydrophilic character on opposite sides of the hydrophobic groups.

Figure 26.3 Semi-empirical molecular model of sodium stearyl phthalamate.

Because of the 40.5° torsional angle in the amide linkage, the hydrophobic aromatic ring and stearyl chain are locked in an “out-of-plane” configuration and provide two distinctly hydrophobic areas in this molecule. The rigid aromatic hydrophobic area is planar while the aliphatic hydrophobic area is linear in nature. This molecular configuration provides for a widely spread hydrophilic head group consisting of the anionic carboxylate and the amide linkage on opposite sides of two distinctly different hydrophobic areas. Based on the unique molecular features of RM1 identified above, a second molecular modeling study was conducted to examine how RM1 molecules pack together. Three aggregate conformations of RM1 were subjected to standard molecular modeling techniques using HyperChem™ software. For comparative purposes, the sodium salt of stearic acid was also modeled as a control. RM1 and sodium stearate were geometrically optimized using semi-empirical techniques. Five molecules of either RM1 or sodium stearate were placed in an aggregate conformation in a periodic “box.” Geometry optimization was performed using molecular mechanics techniques with MM+ force field calculations (see Fig. 26.4). The relative energy of each of these systems was used for comparison of the stability of the aggregate conformations. The lowest energy configuration for an aggregate of RM1 was determined to be where the carboxylates are on alternating sides of the hydrophobic axis (i.e., by rotation of the molecule about the hydrophobic axis). This results in a very stable configuration shown in Fig. 26.4 with a relative energy of -9.6 kcal/mole. Closer inspection of this model shows tight packing of the aromatic rings suggesting a stable orientation. Additionally, less repulsion

Figure 26.4 Geometry-optimized molecular model of RM1 aggregates.

RYKLIN AND BYERS: SHEAR-THINNING LAMELLAR GEL NETWORK EMULSIONS AS DELIVERY SYSTEMS is observed between neighboring molecules of RM1 due to the proximity of the carboxylate hydrophiles. The carboxylate hydrophiles actually pack very well, with the amide oxygen of the neighboring molecule being inserted between them. In contrast, the lowest energy configuration for an aggregated sodium stearate showed the carboxylate head groups of sodium stearate to be packed entirely randomly (see Fig. 26.5). The alkyl chains demonstrate more “randomness” compared with RM1. The calculated energy of this system is in excess of 5.4 kcal/mole, which is significantly greater than the aggregate conformation determined for RM1 (see Fig. 26. 4), even though sodium stearate has fewer atoms than does RM1. When compared to the packing of the traditional soap emulsifier, sodium stearate, the RM1 aggregate configuration has tighter packing, and is more ordered than the sodium stearate in both the hydrophilic and hydrophobic portions of the molecule. Based on the molecular modeling process, we conclude that RM1 is uniquely structured to provide a rigid aggregate at the oil/water interface. A closer look at Fig. 26.4 also suggests the existence of a channel of “hydrophilicity” flowing between the two hydrophobic areas (alkyl chains and aromatic rings) that could entrap water and ionic species, thereby stabilizing a gel network. It is very well known in biology that di-alkyl lipids are the structural element of cell membranes. It is also well known that lipids are an important component of the stratum corneum. On the other hand, polar di-alkyl lipids (such as the lecithins) are natural surfactants with a hydrophobic portion composed

Figure 26.5 Geometry-optimized molecular model of sodium stearate aggregates.

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of two hydrocarbon chains of different lengths. In cells, the components of the cell wall create highly ordered regions which alternate with some disordered regions, and the transition temperature is close to the physiological temperature. In the stratum corneum, the lipids forming the barrier appear to entrap water in a manner similar to a liquid crystalline gel network.[3] From structural considerations, RM1 can be described as a polar di-alkyl compound with two uneven hydrophobic areas (benzene and stearyl). The polar groups separate the two hydrophobic regions by forming an interface that appears to be roughly perpendicular to the two hydrophobic groups. One could assume that when this type of structure is coupled with its unique packing, it can be compared to a natural emulsifier such as lecithin, a Geminitype surfactant, and even a polymeric-type surfactant. Based on our molecular modeling, we conclude that the water appears to be entrapped in emulsions made with RM1 in a manner similar to the way water is entrapped in the cell wall and stratum corneum. The lamellar gel formed by RM1 (see Fig. 26.6) appears to supply more water continuously, because it contains bound water entrapped inside the channels of “hydrophilicity” described above. Consequently, RM1 has a desirable impact on moisturization by providing the presence of additional water molecules. In conclusion, the molecular modeling we conducted suggests that our emulsification technology works through a lamellar gel network, which provides enhanced stability and superior aesthetics to the resulting multiple-phase oil-in-water emulsions. In addition to this lamellar gel network in the water

Figure 26.6 Bilayers with STEPAN-MILD® RM1 aggregates and glyceryl stearate.

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phase, RM1 displays an unexpected behavior during packing that also provides rigidity at the oil/water interface. We can speculate that the unique packing creates hydrophilic channels and tight hydrophobic layers in the water phase. Ionic and other hydrophilic “active” species could be transported through the channels. Hydrophobic components could be incorporated in the tight hydrophobic layers, thus providing a liquid crystalline gel matrix somewhat similar to the stratum corneum and the cell wall.

26.4.3

Interfacial Tension (IFT)

Sodium stearyl phthalamate is insoluble in water at room temperature but, at high temperature, it becomes water soluble and interacts at the oil/water interface displaying strong interfacial tension (IFT) reduction properties, which are critical to the emulsification process. In order to demonstrate the IFT properties, two sets of experiments were conducted to measure IFT. All experiments were performed above 70°C (to insure that the RM1 is dissolved in water). The first experiment relied on the Kruss K12 Tensiometer utilizing the du Nouy ring method. Since this method cannot measure the IFT accurately below 2 mN/M (milliNewton/meter), the second experiment utilized a spinning drop tensiometer. This instrument has the capability of measuring very low levels of IFT from <5 mN/M to 10-6 mN/M. As seen in Fig. 26.7, the data of the first experimental evaluation (the du Nouy ring method) indicated that a 0.1% solution of a combination of STEPAN-MILD® RM1 with a low-HLB emulsifier (glyceryl stearate) at a 2:1 ratio reduces the IFT of water/isopropyl palmitate (IPP) from 31 mN/M down to 1 mN/M.

Results of the second method (spinning drop tensiometer) are shown on Fig. 26.8. The graph illustrates the IFT reduction recorded for different concentrations of sodium stearyl phthalamate at the water/IPP interface with 0.5% low-HLB emulsifier, glycerol monooleate (GMO). A ratio of 2:1 RM1:GMO reduces the IFT of water/IPP below 1 mN/M. This is a sufficiently low IFT to produce the desired effect during emulsification. It allows the emulsifying system to effectively emulsify different types of oils. It is interesting to point out that the IFT graph starts at 1.7 mN/M, which corresponds to 0.1% RM1 in water and 0.5% GMO in IPP. This data point correlated well with the du Nouy ring measurement, suggesting that very low levels of the emulsifying system components at an established ratio provide strong, spontaneous emulsification.

26.5 Identification and Characterization of Lamellar Gel Network Structure 26.5.1

Conductivity Method

Conductivity measurements have proven to be a powerful tool for determining structural changes taking place in the aqueous phase of the multiplephase oil-in-water emulsion. The ability of the RM1 emulsification system to create multiple-phase structured emulsions was characterized by means of conductivity measurements using an Orion Conductivity Meter Model 115. According to the process of emulsion preparation (see Sec. 26.3), the oil phase was added to the water phase, and emulsification was carried out for a standard period of 25–30 minutes with a turbine agitator. During the cool down period, an electrode was introduced into the emulsion, and conductivity data was recorded. Results of the conductivity measurements during the cool down period are demonstrated in Fig. 26.9.

Figure 26.7 Interfacial tension reduction at isopropyl palmitate/water interface at 70°C.

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Figure 26.8 Interfacial tension measurements of STEPAN-MILD® RM1 with 0.5% glycerol monooleate in isopropyl palmitate.

Figure 26.9 Conductivity measurements performed during the cooling phase for emulsions prepared with STEPANMILD® RM1, Pemulen TR-1, and STEPAN® GMS.

The graph shown in Fig. 26.9 clearly identifies the structuring process during the cool-down phase of emulsion preparation with the two distinct phases and a phase-transition temperature being identified by means of their differing conductivity. As can be seen from the graph, conductivity is essentially constant at the elevated temperature of about 75°C and through part of the cooling process, indicating no changes in the aqueous phase of the emulsion. However, a sharp decrease in conductivity is observed at around 45°C. This can be associated with the phase transition temperature (Tc) of the emulsifiers, RM1, and GMS. At this temperature, and below it, the lamellar liquid-crystalline phase created by the sodium stearyl phthalamate based emulsifying system

at elevated temperature converts into a lamellar gel network structure.[3] The sharp decrease in conductivity associated with the phase change of RM1 correlates very well with the idea that, when the hydrocarbon chains of the bilayers of surfactant RM1 molecules solidify (become ordered) at the Tc, the water becomes entrapped in the channels of the network, thereby affecting the conductivity process within the emulsion. Emulsions exhibiting such behavior exist in the form of a lamellar gel network phase at room temperature, and are also referred to as multiple-phase emulsions.[3] Again, we point out such multiple-phase emulsions are not to be confused with the term “multiple emul-

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sions,” which have only two phases, but may occur as oil-in-water-in-oil or water-in-oil-in-water.

26.5.2

Rheological Method

Rheological behavior of emulsions has become increasingly important for today’s formulators in optimizing the performance and sensory attributes of final products.[7] An emulsifying system can be the key to an emulsion’s rheological behavior. Measurements were performed on a prototype RM1-based emulsion containing 15% isopropyl palmitate as the oil phase. Experiments were carried out on a Weisenberg rheometer with a measuring geometry of coaxial cylinders at 22°C–25°C, using standard techniques. The non-Newtonian (viscoelastic) rheological behavior of an emulsion has been attributed to the structure formed by its ingredients.[4] Formation of lamellar gel network structures in an oil-in-water emulsion based on sodium stearyl phthalamate results in an extremely favorable rheological profile. This profile is illustrated by the graphs presented in Fig. 26.10, a and b. The dramatic decrease in apparent viscosity observed with increasing shear rate, as demonstrated in Fig. 26.10a, suggests strong shear thinning flow characteristics. When the data is presented in shear-stress versus shear-rate format (Fig. 26.10b), the overall character of the emulsion’s flow behavior can be seen to be moderately thixotropic with some yield stress. As shear rate increases, the gel “network” structure of the emulsion breaks down, and the viscosity of the system decreases (upper curve). When the shear force is removed, the initial conditions restore, and the structure rebuilds rapidly (lower curve). Moderate thixotropic character can be seen in a slightly lower viscosity in the downward curve versus the upward curve of the graph. Collapse of the lamellar gel network structure due to shear force applied during application of the emulsion to skin results in low viscosity of the emulsion at the high shear rates typical of application. The low infinite viscosity of the product characterizes how emulsion behaves during spreading. Consequently, emulsions based on RM1 demonstrate ease of application as a result of the low viscosity during application. Thixotropy, generally, gives an indication of the degree to which the emulsion flows

into the skin’s valleys. If structure recovers too quickly, the formulation will remain on the skin’s peaks giving a greasy feel. If recovery is too slow (or if there is no structure, as in Newtonian fluids), the formulation will flow into the skin’s valleys, giving a dry feel. The described shear thinning and moderate thixotropic characteristics of the emulsions based on RM1 demonstrate a very favorable rheological behavior, where both of these properties work together to provide a uniform coverage of the skin’s surface. Emulsions containing sodium stearyl phthalamate, therefore, make an extremely effective delivery system for contained actives and provide an exceptional skin feel during and after application.

26.6 Applications 26.6.1

Skin Irritation

Along with extremely desirable functions such as cleansing, foaming, and emulsification, the application of surfactants in personal care products can also cause some adverse reactions upon contact with skin.[8] One example of this is irritation, and as a result, a need for mildness is one of the major requirements for a topical product’s performance. In the case of emulsions, emulsifying systems are well known to play a significant role in the degree of skin irritation of the finished product.[9] The use of emulsifiers in topical formulations is based on their ability to emulsify lipids in water regardless of their origin. Due to this fact, the same emulsifiers used to stabilize the emulsions may, and frequently do, interact with the lipids of the skin and undesirably alter its permeability barrier. The extent of this interaction between emulsifiers and skin lipids depends upon the chemical structure and, consequently, the properties of the emulsifier. Toxicological Studies of RM1. The complete study of the sodium stearyl phthalamate toxicological profile as a raw material was conducted. This included eye and skin irritation, as well as sensitization properties. It was established that RM1 is mild, and does not cause any sensitizing reactions to the skin. Additionally, a study was conducted to compare the mildness characteristics of the final emulsion formulated with sodium stearyl phthalamate-

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(a)

(b) Figure 26.10 (a) Apparent viscosity vs shear rate. The data is indicative of shear-thinning behavior. (b) Shear stress vs shear rate profile for an emulsion (indicative of moderate thixotropy).

based emulsification system. A comparative clinical irritation study of both formulated emulsions was performed by an outside testing laboratory on twentyseven panelists using a cumulative fourteen-day patch test method. The control lotion was based on a conventional anionic system containing TEA/stearate and a polymeric thickener. A similar skin lotion was prepared utilizing the sodium stearyl phthalamate

emulsifying system. Both emulsions contained 15% of isopropyl palmitate. Results of this irritation testing are summarized in Table 26.1. As seen in Table 26.1, the skin lotion based on the sodium stearyl phthalamate system was two categories milder than a similar control composition prepared with the TEA/stearate. The additional mildness provides a significant advantage

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Table 26.1. Cumulative Irritation Test (14 Days, 27 Panelists)

Formulation Tested

Score

Classification

Skin lotion (sodium stearyl phthalamate emulsifying system)

23

Category 1 Mild material – no experimental irritation

Control skin lotion (TEA/stearate/Carbomer)

181

Category 3 Possibly mild in normal use

for formulators working with potentially irritating active ingredients since it enables the formation of a final product with minimal overall irritation. Results of both studies lead to the conclusion that sodium stearyl phthalamate has an excellent safety profile and this behavior is understandable in light of its chemical structure and permeability properties. Due to the fact that RM1 is a relatively large molecule (MW = 440) and is insoluble in water at ambient temperature, it is fair to assume that the material does not disturb the lipid barrier between the skin cells and is, therefore, much milder than conventional emulsifying systems.

26.6.2 Moisturization Effect of RM1 in Creams and Lotions The hydration state of the stratum corneum determines its softness, smoothness, and flexibility. When the rate of water loss from the surface of the skin, promoted by environmental conditions or exposure to solvents or detergent solutions, exceeds the rate of replacement by the body tissue, the stratum corneum of the skin will frequently become rough, chapped, and dry.[10] The function of moisturizing preparations is to increase the water content of this tissue, and a variety of approaches are known. One of the possible ways of providing such moisturizing effects is to create a protective barrier on the skin (occlusive film). Such a film reduces the normal water-loss from the corneum surface to the atmosphere and, therefore, improves its water-holding capacity.[11]

Occlusivity measurements. For practical purposes, the water content of the stratum corneum is measured by an indirect method based on electrical properties of the water.[12] A Nova Dermal Phase Meter, DPM 9003, was employed to evaluate changes in the water-holding barrier properties of stratum corneum as related to the occlusive effect of tested products on the skin. The DPM is an electronic instrument designed to non-invasively measure biophysical characteristics of the skin using an in-vivo capacitance measurement. Capacitance is an electrical (or biophysical) property of skin that provides insight into the level of hydration of the stratum corneum. The stratum corneum has a high electrical resistance by nature, which decreases when moisturized. When the instrument probe is held on the surface of the skin, DPM 9003 produces readouts in DPM units. These units are directly related to the skin’s electrical capacitance, and indicate the amount of water that diffuses through the skin and accumulates under the probe. Lower DPM values indicate improved water-holding barrier properties of the stratum corneum. Lower DPM values may, therefore, be related to the moisturizing, occlusive effect of an applied skin care product. A therapeutic moisturizing cream containing 25% petrolatum and based on a sodium stearyl phthalamate emulsifying system was prepared according to a standard mixing procedure. This cream was compared with neat petrolatum as the positive control, and untreated skin as a negative control. The system was designed to deliver moisturizing occlusive properties.

RYKLIN AND BYERS: SHEAR-THINNING LAMELLAR GEL NETWORK EMULSIONS AS DELIVERY SYSTEMS The study was performed on ten people, both male and female, who ranged in age from 20 to 45 years, and had different skin types. Testing was conducted in controlled conditions of 60%–65% relative humidity and 20°C–22°C. Panelists equilibrated to the environmental conditions for at least thirty minutes before the products were applied. The inner surface of the panelist’s forearm was divided into three squares of 2.5 × 2.5 cm. A standard amount of 30 mg of the test product was gently and uniformly spread in each of two squares with one square remaining untreated. One hour following product application, the probe of the instrument was placed on the skin and readings were taken.

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shows that water loss increases with time following application but is highest for untreated skin and is significantly reduced by using the therapeutic moisturizing cream. Petrolatum, our positive control, is known to be one of the best occlusive ingredients that can reduce transepidermal water loss to almost zero when

The composition of the prototype therapeutic moisturizing skin cream used in the study is shown in Table 26.2. Graphs in Fig. 26.11 demonstrate an example of an occlusivity evaluation on one individual, with “normal” skin. The example illustrates the overall character of the moisturizing effect of the tested products on the skin during a 20-minute measuring period. The figure

Figure 26.11 Occlusivity study on individual with normal skin (one hour after application).

Table 26.2. Therapeutic Cream for Dry Skin with 25% White Petrolatum

Phase

Ingredients D.I. water

Water

q.s. to 100.0

Pemulen TR-1 (Noveon): acrylates/C10-30 alkyl acrylate crosspolymer

0.2

NaOH: sodium hydroxide

0.08

®

STEPAN-MILD RM: sodium stearyl phthalamate ®

Oil

Weight %

1.0

STEPAN GMS PURE: glyceryl stearate

0.5

Penreco Ultima (Penreco): white petrolatum

25.0

STEPAN® IPP: isopropylpalmitate

20.0

®

STEPAN CETYL ALCOHOL, NF: cetyl alcohol

1.0

Germaben II (ISP): propylene glycol, diazolidinyl urea, methylparaben, and propylparaben

1.0

Total oils emulsified

45.0%

pH

7.4-7.6

Appearance

Soft cream

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applied to the skin in a sufficient quantity.[10] Data obtained for petrolatum in our testing confirmed this observation of prior workers. While the electrode was held on the skin covered with petrolatum, all the readings fluctuated slightly around 100 DPM units, indicating that no water diffuses through a layer of petrolatum. On the contrary, when the electrode was placed on untreated skin, moisture was continuously penetrating through unprotected skin and accumulating under the probe. This phenomenon resulted in a constant increase in DPM units. An improvement in skin barrier properties over the untreated skin was obviously demonstrated in the experiment when skin was treated with the therapeutic moisturizing cream containing sodium stearyl phthalamate. In a 20-minute evaluation, water was accumulating under the probe, but to a much lesser extent than it did with the untreated skin.

Visual assessment of skin moisturization. The moisturizing effect of the RM1 formulated emulsion was evaluated using a modified “Scotch®-tape” test followed by visual evaluation under a LEICA GZ6 Stereomicroscope.

Bars in Fig. 26.12 summarize the results of the panel test on people with different skin types. This study allowed us to determine the statistical significance of the RM1-provided improvement in skin moisturization.

The same therapeutic cream formulated with sodium stearyl phthalamate and containing 25% petrolatum that was evaluated in the occlusivity study was also tested against neat petrolatum as the positive control and untreated skin as a negative control. The study included four people with dry skin. After one hour following product application, black electrical tape was pressed to each designated square on the skin, held on the spot for ten seconds, and removed.

Each bar represents an average of readings taken after ten minutes of holding a probe on skin that was treated with a product an hour earlier. Statistical analysis of this study indicates that, with a 95% confidence, the therapeutic moisturizing cream formulated with sodium stearyl phthalamate provided significant improvement in the water-holding barrier properties. As expected, the occlusive effect obtained with neat petrolatum was statistically better than that obtained with the therapeutic moisturizing cream containing 25% petrolatum.

Moisturizing products are used to restore and/ or to maintain a normal function of stratum corneum and prevent appearance of dry skin. The condition of dry skin, which afflicts everyone at some time is either due to environmental conditions, exposure to detergents, or age, and is visually characterized by an appearance of roughness and scaling.[13] The “Scotch®-tape” method is based on evaluating this phenomenon. As a result of the application to and removal of electrical tape from the skin, white dry skin cells adhere to the black tape. The amount of white dry skin cells is inversely proportional to the level of moisturizing effect provided by a product.

The tapes were further viewed under a stereomicroscope to determine the amount of dry cells removed and, thereby, ending up on the tape surface. The results of the tape test are shown in Fig. 26.13. As clearly seen in Figs. 26.13 a, b, and c, skin treated with petrolatum does not show any scaling and looks perfectly lubricated (Fig. 26.13a). On the contrary, untreated skin has a significant amount of large white flakes of dry skin cells (Fig. 26.13b). When skin was treated with the therapeutic moisturizing cream based on sodium stearyl phthalamate, the amount and size of dry skin cells appear to be significantly smaller, indicating strong moisturization and lubrication of skin (Fig. 26.13c).

Figure 26.12 Occlusivity panel study (one hour after application).

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(a)

(b)

559

(c)

Figure 26.13 Moisturizing effect of the products evaluated by the “Scotch® tape” method (X400): (a) neat petrolatum, (b) untreated skin, and (c) therapeutic moisturizing cream.

The results of the tape test show good correlation with the DPM measurements and correlate well with the occlusive effect provided by the same products on the skin. Taken together, these data present a good visual demonstration of the strong moisturizing effect delivered by the emulsion based on RM1, sodium stearyl phthalamate, technology.

sun protective compositions is well known and has been indicated by earlier workers in a number of papers.[14][15]

26.6.3

One of the methods known to the cosmetic industry to increase sun protection factor (SPF) of sunscreen products is to combine inorganic sunscreens (e.g., physical sunscreens such as titanium dioxide or zinc oxide) and organic sunscreens. This approach has a number of advantages:

SPF Enhancement in Sunscreen Formulations

As identified in the above described studies, the emulsifying system based on RM1 provides a structuring effect in the external phase of the emulsion due to a lamellar gel network formation. As a result, formulated products using RM1 display a unique rheological profile that makes them extremely effective delivery systems for active ingredients employed in the emulsion. This effect is especially pronounced when the active ingredients are sunscreen agents. In-vivo evaluations such as SPF static and waterproof tests, were conducted by an independent laboratory. Good correlation with in-vitro studies was observed. This demonstrated that the RM1 emulsifying system provides a synergistic effect of physical and organic sunscreens. Recently, the use of inorganic sunscreens such as titanium dioxide (TiO2) and zinc oxide (ZnO), in combination with organic filters, as well as the sole UV actives has become popular. The key role of an emulsifier system in developing high efficiency

Our work demonstrated that multiple-phase, structured oil-in-water emulsions based on the nonconventional, anionic rheology-modifier–emulsionstabilizer, sodium stearyl phathalamate, serve as an exceptional delivery vehicle when formulating highSPF products with TiO2 and ZnO.

• Physical sunscreens allow reduction of a formulation’s potential for irritation by reducing the amount of organic sunscreens needed and by improving the photostability of chemical actives.[16] • Organic sunscreens enable potential reduction of the undesirable whitening effect associated with physical filters such as TiO2 and ZnO. • A synergistic effect between organic and physical filters is possible that allows the achievement of target SPF numbers with reduced concentration of actives. In addition, such sunscreen formulations are extremely efficient in providing protection over a broad spectrum of UVA and UVB radiation.[16] Some

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DELIVERY SYSTEM HANDBOOK FOR PERSONAL CARE AND COSMETIC PRODUCTS

disadvantages of this formulating route include the remaining potential for irritation, as well as the occurrence of the whitening effect on the skin, if the sunscreen composition is not formulated properly. Titanium-dioxide/organics combination. Titanium dioxide is recognized as a successful inorganic physical sunscreen due to its inert nature and compatibility with different ingredients in formulations. It has been widely used in combination with organic sunscreens in a variety of sun and skin care commercial products. The contribution of the sodium stearyl phthalamate emulsification system to the TiO2/organics sunscreen formulations has been studied in two sets of compositions. The first was being formulated using a conventional anionic system of TEA/ stearate/Carbomer and the second, which contained similar ingredients at the same active levels, was based on the sodium stearyl phthalamate emulsifying system. As demonstrated in Fig. 26.14, an outstanding SPF enhancement of up to 40% was achieved in a system containing RM1 compared to a conventional emulsion employing the same level of sunscreens. Obtaining desirable waterproofing properties are an important aspect of formulating sun protection creams and lotions. The same prototype formulation based on sodium stearyl phthalamate and containing micronized TiO2 (3.2% active) in combination with 3.5% ethylhexyl-p-methoxycinnamate and 1.5% benzophenone-3 was also tested by the inde-

pendent laboratory for the waterproof SPF. The study was conducted in vivo, on five subjects, on a skin type 1, 2, or 3. According to the procedure of the method, panelists were subjected to four immersions in water for twenty minutes each. The results of this study are shown in Table 26.3. Table 26.3. RM1 Impact on SPF Waterproofing Formulation

Stepan Formulation

In vivo static SPF

23

SPF waterproof

22

As seen in Table 26.3, there was a strong waterproofing effect using RM1without adding any waterproofing agents. The intrinsic waterproofing effect of STEPAN-MILD® RM1 can be understood to be related with the water insolubility of the RM1 molecule at ambient temperature and, consequently, its desirable inability to re-emulsify oils upon contact with water. Another extremely important aspect of formulating physical sunscreen-containing emulsions using RM1 can be demonstrated by the micrograph in Fig. 26.15. Extensive work with micronized, hydrophobically treated, titanium dioxide (TiO2) suggests that the RM1 emulsification technology generates oil-in-water emulsions with the inorganic sunscreens that are well encapsulated in the oil phase. Figure

Figure 26.14 SPF values represent average of measurements performed in vitro and in vivo.

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emulsifiers such as C 10-30 alkyl acrylate crosspolymers in one formulation. Such systems are widely used in the cosmetic industry to stabilize emulsions,[19] and there is a need to find ways around this problem. A series of experiments were conducted to evaluate the role of sodium stearyl phthalamate in providing compatability of ZnO with a widely-used polymeric emulsifier (acrylates C10-30 alkyl-acrylate crosspolymer).

Figure 26.15 Micrograph of sunscreen emulsion with micronized TiO2 water-resistant SPF 25 (X600).

26.15 demonstrates the micrograph of an RM1-based sunscreen emulsion with micronized TiO2 (3.2% active TiO2 in combination with 3.5% ethylhexyl-pmethoxycinnamate and 1.5% benzophenone-3). An extremely uniform distribution of oil droplets containing encapsulated TiO2 can be noted. Uniform and effective dispersion of TiO2 within the oil phase of the emulsion, as shown in Fig. 26.15, combined with the ability of the RM1 technology to uniformly distribute and deliver these particles to the skin surface, results in a desirable, non-whitening effect. This effect was positively identified by a visual panel evaluation. Zinc-oxide/organics combination. As far as it is currently known, sunscreen formulations comprising combination of zinc oxide and organics are less common.[17] Nevertheless, the increasing demand to provide “broad spectrum protection,” as well as the trend to incorporate UV filters in the daily use skin care and other cosmetic products, continue to stimulate an increasing interest in such combinations. Significant advantages of ZnO as a sunscreen agent include its effectiveness in blocking UVA and UVB radiation, photostability for effective coverage throughout a day, and a long history of safety. However, there are some limitations of using ZnO that are attributed to a very reactive nature of this product and the accompanying problems of formulation stability.[18] In addition, the formulating experience in the industry indicates that it is very difficult to combine zinc oxide and polymeric thickeners/

The prototype formulation shown in Table 26.4 is a result of extensive optimization work, and demonstrates the unique ability of sodium stearyl phthalamate to provide stable and effective emulsions containing both polymeric emulsifier (acrylates C10-30 alkyl-acrylate crosspolymer) and ZnO. The stability of developed compositions was monitored at both ambient and elevated temperatures. Freezethaw testing was conducted as well. Incorporation of ZnO and it’s distribution in the oil and aqueous phases of the emulsion play an important role in achieving desired emulsion stability (both in terms of pH and temperature), as well as SPF values. Extensive microscopy work has been performed to study these phenomena and effects. Visual monitoring of the emulsion’s structure was conducted using an optical microscope (Olympus BH2) at 400X magnification. The formulation shown above in Table 26.4 was observed under the microscope after storage for one month, at ambient, and 45°C. Micrographs (a) and (b) in Fig. 26.16, illustrate the effect of storage at different temperatures on emulsion structure and the potential for phase separation. As the photomicrographs demonstrate, the initial oil droplets small size and uniform distribution are very good, with ZnO clearly incorporated in the oil phase of the emulsion. Storage at elevated temperature for one month caused some insignificant coalescence of oil droplets and resulted in very slight oil droplet enlargement. Overall droplets size and distribution, however, remained very similar to the initial droplet size and distribution of the oil phase within the emulsion. These observations prove good high temperature stability of the formulation and correlate with visual observations of the stability of the sample stored in the oven.

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DELIVERY SYSTEM HANDBOOK FOR PERSONAL CARE AND COSMETIC PRODUCTS

Table 26.4. RM1 Complete UV Protective Lotion with ZnO and Ethyl-P-Methoxycinnamate (SPF 24.6*)

Phase

Ingredient

Weight %

D.I. water Water

q.s. to 100.0

Pemulen TR-1 (Noveon), acrylates/C10-30 alkyl acrylate crosspolymer

0.2

NaOH, sodium hydroxide

0.07

STEPAN-MILD® RM1, sodium stearyl phthalamate

1.0

STEPAN OCTYL ISONONANOATE®, ethylhexyl isononanoate Dow Corning 345 fluid (Dow Corning), cyclomethicone

2.0

Parsol MCX (Givaudan-Roure), ethylhexyl-p-methoxycinnamate

6.0

®

Oil

10.0

Z-Cote HP1 (BASF), zinc oxide and dimethicone

3.0

STEPAN® GMS PURE, glyceryl stearate

0.5

STEPAN® CETYL ALCOHOL, NF, cetyl alcohol

1.5

®

STEPAN STEAROL ALCOHOL 97, stearyl alcohol

1.5

Vitamin E (Roche), tocopheryl acetate

0.05

Germaben II (ISP), propylene glycol, diazolidinyl urea, methylparaben, and propylparaben

1.0 9.0% 8.2–8.5 Lotion

Total Sunscreens pH Appearance *In vivo (6 individuals).

(a)

(b)

Figure 26.16 Micrographs showing the effect of elevated temperature on emulsion structure (X400): (a) 1 month at RT, (b) 1 month at 45°C.

RYKLIN AND BYERS: SHEAR-THINNING LAMELLAR GEL NETWORK EMULSIONS AS DELIVERY SYSTEMS The best prototype formulations were tested in vitro and in vivo by outside testing companies in order to confirm the expected, broad-spectrum protection. An in-vivo study was performed using a labsphere ultraviolet transmittance analyzer, in the range of wavelengths covering both UVA and UVB ranges from 290 nm to 450 nm. Final SPF numbers represented an average of four runs for each sample. In-vivo testing was done on six subjects of skin type II. This type of skin represents “sensitive” skin, that always burns easily and tans minimally. Table 26.5 demonstrates the in-vitro and in-vivo SPF values as well as critical wavelengths (CW) for the tested composition (Table 26.4). As seen in Table 26.5, the prototype formulation demonstrates a strong synergistic effect of ZnO and OMC (ethylhexyl-p-methoxycinnamate). This results in a high protection for sunlight in the UVB range, and a sufficient UVA protection as measured by Boots 1–5 star system. Formulating with inorganic sunscreens as the only active. The well-known, strong commercial trend of using physical UV filters as the sole sunscreen active is attributed to concerns by dermatologists about irritation and the allergic potential of organic sunscreens for infants, children, and people with sensitive skin. Inorganic blocking agents such as ultrafine TiO2 and ZnO attenuate UV light via a combination of absorption and scattering. They are also known to provide a broader wavelength range of protection than most chemical sunscreens. In addition, physical sunscreens are biodegradable, chemically inert, and essentially nonirritating. The biggest challenge in formulating with inorganic sunscreens as the only active is the difficulty in achieving high SPF values. This is especially true in oil-in-water emulsions. Further, such formulations with a high concentration of

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physical sunscreens will impart an undesirable whitening effect to the skin. Extensive formulation work has been conducted to develop prototype formulations with TiO2 and combinations of TiO2 and ZnO at different concentrations with up to 12% actives. In addition to standard stability requirements at ambient and elevated temperatures, these compositions were also evaluated for the level of protection provided and aesthetic properties obtained. Some examples of sample formulations are shown in Formulations 26.1 and 26.2 in Sec. 26.8. Results of in-vivo testing on four subjects by an independent laboratory demonstrate a high ratio of SPF units per active percent of physical sunscreens (more than 3), a ratio not easily achieved with conventional emulsifiers where agglomeration of physical sunscreens is more likely to occur. As identified through extensive microscopy studies (see example shown on the micrograph in Fig. 26.15) uniform and effective dispersion of TiO2 within the oil phase of the emulsion, combined with the ability of the RM1 technology to uniformly deliver and distribute the sunscreen particles on the skin, results in a highly desirable, non-whitening effect as previously described. The sodium stearyl phthalamate-based emulsification system has been found to be extremely efficient in formulating high-SPF, broad-spectrum UV protection skin and sun care products. The results of the conducted work described in this chapter demonstrate that the sodium stearyl phthalamate based emulsification system allows formulators to achieve a variety of desirable objectives. These include target performance with reduced level of actives, SPF enhancement for combinations of inorganic and organic sunscreens, minimization of the whitening effect of ZnO and TiO2 on the skin, and shiny emulsions with a pleasant, light skin feel.

Table 26.5. Results of SPF Testing (on Formulation Shown in Table 26.4) Product

In vivo SPF

Critical wavelength (CW), nm

Mean absorbance ratio

Boots star rating

In vitro SPF

Emulsion with ZnO

24.6

370

0.42

✯✯

23.0

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It was also discovered that sodium stearyl phthalamate provides the unique possibility of combining ZnO with acrylates/C10-30 alkyl acrylate crosspolymers in sunscreen formulations. This ability is highly attractive since it solves a previously unachievable goal of the industry.

26.6.4 Formulating Sprayable Products Sprayable lotions are gaining more and more popularity in the market place. This is attributed to a number of advantages of spray delivery systems. Some of the conveniences include the ease of application as well as improved product coverage on the skin. However, as cosmetic chemists are well aware, formulation of sprayable products presents a major challenge. The challenge is attributed to the fact that, on one hand, sprayable lotions should have low enough viscosity to be sprayable, while on the other hand, viscosity should be high enough to provide desired shelf life and stability of the finished product. One answer to this challenge is to provide a system with an optimum emulsion rheological profile. Such a profile will require high shear thinning behavior (low viscosity) of the emulsion at high shear rates (spraying) and relatively high viscosity at lower or zero shear rates typical of shelf life stability and pouring. The ability of an emulsion to quickly recover its high viscosity on the skin after application at high shear is critical to prevent dripping from the skin surface. Selection of an appropriate emulsification system is key to providing the desired rheological behavior of the emulsion. The formation of the RM1-based lamellar gel network structure in formulated products, combined with the desirable shear thinning flow characteristics of resulting structured multiple-phase emulsions, were demonstrated earlier in this chapter and have proven to be extremely favorable in formulating sprayable skin lotions. An example of one of such product is presented in Formulation 26.3 in Sec. 26.8. The relatively high initial viscosity of 2,000 cps at low shear rates insures good physical stability of the product (up to one month at 50°C with no separation), and, consequently, an adequate shelf life.

Collapse of the lamellar gel network structure due to high shear force during spraying results in a desirably low emulsion viscosity and good sprayability properties of the product. Rapid recovery of the structure prevents the product from running off the surface of the skin. Rubbing the product on the skin during the application process creates high shear rates again and consequent reduction of the product’s viscosity due to shear thinning properties of the emulsion. This provides ease of application and good spreading of the product on the skin. Moderate thixotropy of the emulsions based on RM1 ensures uniform coverage of the skin surface. As was confirmed in panel testing, sprayable lotions containing sodium stearyl phthalamate demonstrate an exceptional skin feel during and after application.

26.7 Conclusion The emulsification technology presented in this chapter works through liquid gel network formation that provides stability and superior aesthetics in multiple-phase, oil-in-water emulsions. The emulsifying system containing STEPAN-MILD® RM1 improves delivery of cosmetically active ingredients such as sunscreens, silicones, moisturizers, and vitamins; and results in highly efficient products. The RM1 emulsifying system displays a synergistic effect with physical sunscreens in a combination with organic sunscreen agents, as well as imparting waterproofing of finished formulations. RM1 also provides a unique solution to the previously unsolved problem of the desire to combine a polymeric emulsion with a polyvalent element (zinc in zinc oxide). The emulsions based on this technology are extremely mild and are highly efficient in providing a strong occlusive effect on the skin which translates into enhanced skin moisturization and improvement in a “dry skin” condition. The unique combination of attributes described in this chapter make the emulsification technology implementing sodium stearyl phthalamate an ideal candidate for formulating elegant moisturizing products, including creams and lotions for sensitive skin.

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26.8 Formulations In addition to the sample formulations presented here (Formulations 26.1 through 26.3), see Table 26.2 “Therapeutic Cream for Dry Skin with 25% White

Petrolatum,” and Table 26.4 “RM1 Complete UV Protective Lotion with ZnO and Ethyl-P-Methoxycinnamate.”

Formulation 26.1: Water Restistant UVA/UVB Sunblock for Babies with TIO2 (SPF 26.0*)

Phase

Ingredient D.I. water

Water

q.s. to 100.0

Carbowax PEG 400 (Dow Chemical) PEG-8

4.0

Pemulen TR-1 (Noveon), acrylates/C10-30 alkyl acrylate crosspolymer

0.2

NaOH, sodium hydroxide

0.09

®

Oil

Weight %

STEPAN-MILD RM1, sodium stearyl phthalamate

1.0

Finsolv TN (Finetex), C12-15 alkyl benzoate

13.0

STEPAN® OCTYL PALMITATE, ethylhexyl palmitate

11.0

Dow Corning 345 (Dow Corning), cyclomethicone

3.0

Ganex V-216 (ISP), PVP/hexadecene copolymer

2.0

Eusolex T-2000 (EMD Chemicals) titanium dioxide, alumina, and simethicone

10.0

STEPAN® GMS PURE, glyceryl stearate

0.5

Vitamin E acetate (Roche), di-alpha-tocopheryl acetate

0.1

Germaben II (ISP), propylene glycol, diazolidinyl urea, methylparaben, and propylparaben

1.0

Total Sunscreens PH Viscosity @ 25°C Brookfield RV 6 @ 20 rpm (cps) Appearance * Screening in-vivo testing

8.0 7.0–7.2 Lotion

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Formulation 26.2: Sensitive Skin Complete UV Protective Sunblock with TiO2 and ZnO (SPF 32.3*)

Phase

Ingredient D.I. water

Water

Oil B

q.s. to 100.0

Carbowax PEG 400 (Dow Chemical) PEG-8

4.0

Pemulen TR-1 (Noveon), acrylates/C10-30 alkyl acrylate crosspolymer

0.2

NaOH, sodium hydroxide

0.09

STEPAN-MILD® RM1, sodium stearyl phthalamate

1.0

®

Oil A

Weight %

STEPAN OCTYL PALMITATE, ethylhexyl palmitate

10.0

Z-Cote HPI (BASF), zinc oxide and dimethicone

3.0

®

STEPAN GMS PURE, glyceryl stearate

0.5

WECOBEE® S, hydrogenated vegetable oil

1.0

Finsolv TN (Finetex), C12-15 alkyl benzoate

15.0

Ganex V-216 (ISP), PVP/hexadecene copolymer

2.0

Eusolex T-2000 (EMD Chemicals), titanium dioxide, alumina, and simethicone

10.0

Germaben II (ISP), propylene glycol, diazolidinyl urea, methylparaben and propylparaben

1.0

Total % Sunscreens

11.0

PH

8.0–8.5

Viscosity @ 25°C RV 6, 20 rpm (cps)

25,000

Appearance * Screening in-vivo testing

Soft cream

RYKLIN AND BYERS: SHEAR-THINNING LAMELLAR GEL NETWORK EMULSIONS AS DELIVERY SYSTEMS Formulation 26.3: Sprayable Lotion with Silicone

Phase

Ingredient D.I. water

Water A

C

q.s. to 100.0

Propylene glycol

1.0

Pemulen TR-1 (Noveon), acrylates/C10-30 alkyl acrylate crosspolymer

0.2

NaOH, sodium hydroxide

0.08

STEPAN-MILD® RM1, sodium stearyl phthalamate

1.0

Versene NA (Dow Chemical), disodium EDTA

0.1

®

0.5

®

NEOBEE M-5 cosmetic, caprylic/capric triglyceride

1.0

STEPAN® OCTYL ISONONANOATE, ethylhexyl isononanoate

2.0

DC 345 fluid (Dow Corning), cyclomethicone

1.0

Propylene glycol

1.5

Germaben II (ISP), propylene glycol and diazolidinyl urea and methylparaben and propylparaben

1.0

STEPAN GMS PURE, glyceryl stearate Oil B

Weight %

Citric acid Total oils emulsified pH Viscosity @ 25°C Brookfield RV 4 @ 20 rpm cps Appearance

q.s. to pH 7.0–7.5 4.0% 7.0–7.5 2,000 Lotion

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References 1. Fox, C., In Introduction to Multiple Emulsions, Cosmetic & Toiletries, 101:101–112 (1986)

10. Middleton, J., Methods of Skin Moisturizing, Cosmetic & Toiletries, 92:34–38 (1977)

2. Friberg, S., and Larsson, K., Liquid Crystals and Emulsions, Advances in Liquid Crystals, (G. M. Brown, ed.), Vol. 2, pp. 173–195, Academic Press, London (1976)

11. Rieger, M., Skin, Water and Moisturization, Cosmetic & Toiletries, 104:41–51 (1989)

3. Eccleston, G., Multiple-phase oil-in-water emulsions, presented at the Annual Meeting of the Society of Cosmetic Chemists, New York, pp. 1–22 (1989) 4. Rena, L., et al., Secondary Structural Rheology of a Model Cream, J. Soc. Cosmetic Chemists, 45:77–84 (1994) 5. Suzuki, et al., Secondary Droplet Emulsion: Contribution of Liquid Crystal Formation to Physico-Chemical Properties and Skin Moisturization Effect of Cosmetic Emulsions, Abstracts, IFSCC in Paris, I:117–137 (1992) 6. Goze, J., et al., Patent # WO 91/01970, Cyclic Amidocarboxy Surfactants, Synthesis and Use Thereof, (Dec. 1996) 7. Dahms, G., Choosing Emollients and Emulsifiers for Sunscreen Products, Cosmetic & Toiletries, 109:45–52 (1994) 8. Rieger, M., Surfactant Interactions with Skin, Cosmetic & Toiletries, 110:31–50 (1995) 9. Ghyczy, M., and Vacata, V., Concepts for Topical Formulations Adjusted to the Structure of the Skin, Chinica Oggi, 9:17–20 (1999)

12. Tagami, H., Quantitative Measurements of Water Concentration of the Stratum Corneum, Acta Dermatovenerologica (Stockh.), pp. 29–33 (1994) 13. Morizot, F., et al., Sensitive Skin, Cosmetic & Toiletries, 113:59–65 (1998) 14. Hewitt, J. P., Advances in Physical Sunscreens, Global Cosmetic Industry, p. 29, (2000) 15. Dahms, G. H., Formulating with a Physical Sun Block, Cosmetics and Toiletries, 107:87 (1992) 16. Hewitt, J. P., Novel Formulation Strategies for High SPF and Broad Spectrum Sunscreen products, First European UV Sunfilters Conference, Paris (1998) 17. Mitchnik, M., Zinc Oxide, An Old friend to the Rescue, Cosmetic & Toiletries, Vol. 107 (Oct., 1992) 18. Johncock, W., Sunscreen Interactions in Formulations, Cosmetic & Toiletries, Vol. 114 (Sep., 1999) 19. Chiarelli, J., et al., Sunscreen Composition, Patent W/O 99/15144 (Apr., 1999)

Acknowledgment A number of Stepan employees contributed to the work described in this chapter, and their help is greatly appreciated. Some of the material included in this chapter was first presented at the Advanced Technology Conference: Europe, 1998, in a paper entitled “Versatile and Efficient Emulsification Technology Based on a Non-Conventional Anionic Rheology Modifier.” Other information was presented at the 2000 Cesio

Conference in a paper entitled, “Use of Non-Conventional Lamellar Gel Network Technology for Producing Elegant Moisturizing Creams and Lotions,” and at the XXI IFSCC International Congress 2000 in a paper entitled, “Formulating Efficient Broad Spectrum UV Protection Oil-in-Water Creams and Lotions with Zinc Oxide.” This material is used with the permission from Cosmetics and Toiletries Magazine, Cesio, and IFSCC.