Document 8R0jvrMmrDqRdDkmxO8JpZZ1m

AEROSOL EMULSION SYSTEMS by P. A. Sanders "FREON" PRODUCTS DIVISION E. I. DU PONT DE NEMOURS & COMPANY, INC. WILMINGTON 98, DELAWARE MEETING OF TOILET GOODS ASSOCIATION NEW YORK CITY DECEMBER 20, 1957 Reproduced with the permission of the Editors, Journal of the Society of Cosmetic Chemists. The original article was published in Voi. IX, No. 5, September, 1958 0) O to 9 UJ The first aerosol products and the majority of the aerosol products today were formulated as homogeneous systems in which all of the components of the formulation were mutually soluble. In these products the pressure supplied by the propellent forces the solution of active ingredients, solvents and propellent up the stanppipe and tnrough the valve. As the solution leaves the valve the iiquefiec propellent changes into a gas and blasts the solution of active ingredients into fine particles. There are, however, many materials that would be desirable to spray as aerosols that are soluble in water and have only limited solubility in organic solvents, '"ater is incompatible with the fluorinated hydrocarbon propellents and the formulation of aqueous-based aerosols giving satisfactory sprays has presented many difficulties. As discussed by Callans (1), the successful formulation of aqueous-based aercso!s in the future should lead to a much wider variety of products than are new possible with the homogeneous systems alone and should result in a consideraDle expansion of the aerosol market It is the purpose of this paper to present the various aerosol systems that have been proposed in the attempts to spray aqueous-based products with particular em phasis upon the water-in-oil emulsion systems. THREE-PHASE SYSTEMS One of the first successful methods for spraying aqueous systems resulted from the development of the ''three-phase" system by Eaton (2) and Mina (3). In this system, the aqueous solution is layered over the denser fluorinated hydrocarbon propellent, which provides the pressure necessary to force the aqueous phase through the stand pipe. The latter extends only into the aqueous phase. Since there is essentially no propellent dissolved in the aqueous phase as it passes through the valve, atomization is obtained by the mechanical shearing action of a special valve rather than by flashing of dissolved propellent. At the present time, such valves produce relatively coarse sprays with these systems. oil-in-water emulsion Aerosol products formulated as oil-in-water emulsions have been on the market since about 1950. These products are the well-known and widely accepteq shaving lathers. In tnese products, a relatively small amount of propellent, usual1 y aaout 3 to 1C per cent, is emulsified in an aqueous soap solution. As the emulsion is dischargee from the foam valve, the propellent expands, forming countless small bubbles. These give the rich lather characteristic of this type of system. Attempts to obtain fine sprays from such systems by increasing the proportion cf propellent and using a spray valve instead of a foam valve result in products which stream. Excessive foaming occurs when the steam impinges on a surface. A series of oil-in-water formulations (4) has been developed that give relatively wet sprays and are essentially nonfoaming. These formulations have low concentrations of propellent, usually less than 5 per cent. By the use. of auxiliary solvents, such as ethyl alcohol, almost transparent systems are obtained. These systems have the advantage that no creaming occurs during standing and shaking of the formulation before use is net necessary. 2 EID11610 Window cleaning formulations employing the low propellent oil-in-water system have been marketed for several years and have been well received. These formulations g>ve a soft SDray and foam slightly on glass. WATER-IN-OIL EMULSIONS During the past several years the Du Pont Company has carried out studies on aoueous-based aerosol systems in an attempt to extend the range of SDray character istics of the water-based aerosol products. This has been found to be possible with the water-in-oil emulsion systems. With such systems, spray properties varying from coarse to very fine may be achieved (5). It was considered initially that the water-in-oil emulsions should have a fairly good chance of producing nonfoaming sprays. In such systems the water is dispersed throughout the propellent. As the emulsion is forced through the spray actuator, the propellent evaporates, leaving the water droplets, the emulsifying agent, and any auxiliary solvents present. Since very little propellent is dissolved in the aqueous droplets, there is less tendency for the vaporizing propellent to cause foam formation with the droplets. Likewise, since the emulsifying agents suitable for water-in-oil emulsions are generally oil soluble, they are usually poor foaming agents for aqueous solutions. In choosing the series of emulsifying agents to study, considerable use was made of the list of synthetic detergents assembled by McCutcheon (fc). A wide variety of agents were chosen from this list with the selection confined generally to the oilsoluble or known water-in-oil emulsifying agents. The ultimate selection of the most satisfactory emulsifying agents was based upon the stability of the emulsions, the lack of foaming with the sprays, and the lack of corrosion resulting from the water-in-oil emulsions in metal containers. Of all the agents that were investigated, the polyglycerol esters of the fatty acids were found to be the most satisfactory. Surface-active agents of this type are Emcol 14 (Emulsol Chemical Company) and Solecnic PGE (Sole Chemical Company). Emcol 14, a waterin-oil emulsifying agent, was used exclusively for the preparation of the emulsions described in this paper. In addition to its emulsifying properties, it is reported to be an antifoaming agent (fe). Another effective water-in-oil emulsifying agent for the aerosol systems was Soan 20 (sorbitan monolaurate. Atlas Powder Company). This material also is reported to possess antifoaming properties (7). There are, without doubt, many other surface active agents that would also be effective for preparing aerosol water-in-oil emulsion systems. However, in view of the large variety and number of agents that are commercially available and the time re quired to evaluate a given agent, it was not possible in the present study to test all materials that conceivably might have been effective. EID11611 EVALUATION OF EMULSION STABILITY AND SPRAY CHARACTERISTICS The true stability of the emulsion systems as determined by size-frequency analysis was not determined. However, visual observations of the creamed-aqueous pnase at various intervals showed that no observable coalesence of the dispersed water drops had occurred with the emulsions that are discussed in the present paper. Although creaming in an emulsion is not a sign that the emulsion is unstable, it is commercially important because an emulsion that has creamed must be shaken before use. In the present case, rate of creaming is indicated by "separation times." This is the time interval after shaking of the emulsions before visible separation of the two phases occurs. Separation times were determined within one hour after pre paration of the emulsions. In many cases it was observed that the separation times for a given series of emulsions changed considerably after the emulsions had aged. The emulsions were packaged in coated glass bottles for visual observation. The spray characteristics of the emulsions as reported in the tables were determined with a standard glass-bottle valve. In practically all cases, changing from standard actuators to mechanical break-up type of actuators will produce a much finer spray. In many instances, emulsions that stream with the standard actuator will spray with the mechanical break-up type. '`FREON11"* PROPELLENTS STUDIED The propellents involved in the study were "12" (dichlorodifluoromethane), "114" (dichlorotetrafluoroethane), "11" (trichloromonofluoromethane), and "113" (trichlorotrifluoroethane). Although "11" and "113" are not normally considered as propellents because of their relative low vapor pressures at room temperatures, they will be considered as such in the present paper for ease of discussion. EXPERIMENTAL RESULTS Emulsion Stability with the Indii idual Propellents (l~) The relative stability of water-in-oil emulsions prepared with the individual propellent compounds is as follows, in decreasing order: "11".- "113"> "12," "114." In Table 1 are listed the separation times for the emulsions prepared with various propellent, water ratios. The relative stability of the emulsions prepared with the propellent compounds corresponds roughly to the solvent properties of the compounds. This is indicated by a comparison of the Kauri-butanol values (8) for the propellent compounds that are also listed in Table L Actually propellent "12" and propellent "114" are such limited solvents that the Emcol 14 used as the emulsifying agent was not sufficiently soluble to form good emulsions. * Referred to by number only in remainder of paper. 4 EID11612 Table 1--Emulsion Stability of Propellent-Water Systems t Propellent W'ater --TL'miil.siun <-* 'ti 'i1me Ratio, Wt. % Propellent "12" Propellent "114'' Propellent " 11" Propellent "113' V) 10 80 70 60 40 40/bO Kauri-Butanol values of propellents <1 min. T1 min. <1 min. 1-5 min. 18 < 1 mm. <1 min. <1 min. 15-30 min. 11 8 1 5-30 min. 15-30 mm. >1 nr. > 1 hr. 60 1 1-5 min. 1-5 mm. > 1 hr. >1 hr. 32 f 4 parts or Emcol 14/104 parts ot emulsion. PROPELLENT-WATER EMULSIONS Satisfactory water-in-oil emulsions with "12". "114" solutions or "114" alone as the propellent have not yet been achieved. As previously mentioned, these two propellents have limited solvent properties and the surface active agents in general were not sufficiently soluble in the propellents to form stable emulsions. Propellents "12"/ " 11"/Water Emulsions Fairly satisfactory emulsions may be obtained by combining "11", with its relatively good solvent powers, with "12." The spray characteristics of the emulsions may be varied from very fine to very wet by varying either the "12"/"11" ratio or the propellent/water ratio. The effect of varying the "12"/"11" ratio upon spray characteristics and emulsion separation times is shown in Table 2. The variations were tested at propellent/water ratios of 80/70 and 60 40, respectively. As the data in Table 2 2--Table Effect of Variation in Propellent "12". Propellent "11" Ratio Upon Emulsion and Spray Properties Propellent 12' IT Ratio, Wt. % Separation Times Rprav Charac teristics ProDellent 12','ll' Ratio. Wt. % Reparation Times Spray Characterisrics 80 20 Propellent 'Water Ratio 100.0 "0 30 <1 min. <1 min. Very- fine 50 50 30 70 0/100 1-5 min. 15-30 min. 15-30 min. Fine Medium fine No spray b0 40 Propellent Water Ratio 100,0 70 30 50 50 30-70 0/100 <1 min. 30-b0 min. 30-b0 min. 30-60 min. >1 hr. Fine Medium fine Soft medium No spray 4 parts Emcol 14/104 parts final emulsion indicate, increasing the proportion of "11" in the propellent mixture increases the stability of the emulsions and also the wetness of the spray. Both of these effects would be predicted on the basis of the data in Table 1 and the fact that "11" lowers the vapors pressure of "12," thus giving propellent mixtures that produce coarser sprays. EID11613 5 The effect of varying the propellent,water ratio upon emulsion stability and spray characteristics is given in Table 3. In these experiments the "12" "11'' ratio was held constant at 30 70. Table 3--Effect of Variations in Propellent* Water Ratio Upon Creaming and Spray Characteristics Propellent Water Ratio, Wt. % 90/10 80/20 60/40 40/60 20/80 Separa non Times 1-5 min. 5-15 min. 30-60 min. > 1 hr. <1 min. Sprav Characteristics Verv fine Fine Medium Very coarse--almost foams Stream--roams Emulsions prepared with 4 parts Emcol 14 T04 parts of finished emulsion * Propellent is "12"/" 11" (30/70:. In this series, increased emulsion stability and increased wetness of sprays result with a decrease in the propellent/water ratio. The increase in stability probably results primarily from the increase in viscosity of the emulsions that occurs as the proportion of water is increased. This point will be discussed in more detail later. Emulsions of ''12"11" generally exhibit slight bubbling when sprayed on a surface. For some uses, this may be undesirable. The bubbling probably results from vaporization of the "11" that is retained in the spray. Emulsions uith Auxiliary Solvents The use of auxiliary solvents, such as odorless mineral spirits, has a number of advantages in formulating aerosol water-in-oil emulsions. As shown later, the solvents may increase emulsion stability, particularly with emulsions formulated with "12" alone or "12" "114" solutions as the propellents. As previously noted, "12" "11" water emulsions tend to cause bubbling when sprayed on a surface. The addition of an auxiliary solvent may minimize or eliminate the bubbling entirely. The ease of preparation of the emulsions is increased considerably by the use of solvents. For example, the solvent may be used to dissolve the water-insoluble surface-active agent. A water-in-oil emulsion is then prepared from the solvent by adding the water to the solvent. This emulsion is used to fill the aerosol container. The propellent is pressure loaded after capping the container. In this case, the ad dition of propellent to the previously formed emulsion can be considered merely as extending the continuous oil phase. Under the present ICC regulations, "12"/water emulsions would not be per missible in the standard aerosol containers as a result of pressure limitations. Auxiliary solvents serve as pressure depressants for "12" and permit the formulation of emulsions using "12" alone as the propellent. 6 EID11614 Propellent "12" Solvent/Water Systems Emulsion systems of "12'' oaorless mineral spirits water produce nonfoaming sprays. The soray characteristics themselves may be varied over a wide range from very fine to very coarse by changing the "12" solvent ratio. Examples of this are ' ;sted in I able 4. Table 4--Propeller-- "12" Odorless Min era l Spirits Wat er Emulsions Propellent "12" QMS* H-0 Ratio, Wt. % ------- Separation Times------ Without "12" With "12" Sprav Characteristics r/j '20 20 40-20. 40 20 '20 00 oO 30 10 60 TO '30 >1 hr. >1 hr. >1 hr. 5-1 5 .min. >1 hr. 1-5 min. >1 hr. > 1 hr. 1-5 min. 1-5 min. Fine Medium Wet Fine Fine 4 parts Emcol 14 '!H4 parrs of finished emulsion * OMS = Odorless mineral spirits. As discussed previously, "12"/water emulsions of satisfactory stability were not obtained. As shown by the data in Table 4, the effect of the odorless mineral spirits is to increase the emulsion stability considerably. A comparison of the stability of the odorless mineral spirits, water emulsions before and after the addition of "12" is also shown in order to indicate the effect of the "12" upon the emulsion stability. Propellent "12" decreases the emulsion stability but in most cases the stability is still sufficient for practical purposes. Odorless mineral spirits is one of the best solvents for obtaining nonfoaming sprays. For certain applications, other solvents such as cottonseed oil may be more desirable. These solvents form fairly good emulsions but in some cases there appears to be a tendency to promote slight bubbling or foaming. Propellent " 1 2"/" 1 H"/Odorless Mineral Spirits Water Emulsions Pressure of 25 psig. or less at 70F, are generally considered desirable for aerosols to be packaged in glass. In "12" odorless mirferal spirits, water systems pressures below 25 psig may be achieved by the proper ratio of propellent to solvent. As discussed later, however, the extent to which this can be done is limited by flam mability considerations. In order to obtain pressures below 25 psig. it may be necessary to have such a low propellent, solvent ratio that the product is flammable. It is also found that emulsions with sufficiently low "12"/odorless mineral spirits ratios to satisfy the pressure requirements generally give excessively wet sprays. The above difficulties may be eliminated by formulating with "12"/"114" solutions as the propellent. Emulsion systems producing sprays ranging from very wet to fine may be obtained by varying the ratio of "12" to "114." The propellent solu tions with a low concentration of "12, ".that would be satisfactory for glass bottle aerosols, give very soft sprays. EID11615 Tab.e 5---Propellents "12..... 114" /Odor LESS Min ERA l Spirits 'Water Emulsion Propellents "12"'"!:4" Ratio. Separation Times Spray Charac ter'sties Propellents "12" "114" Ratio, 'A t. c~c Separation Timer) Spray Charac teristics Propellent Solvent H aler 0. 100 1-5 mm. 1; 85 1-5 mm. 40 '60 57 43 100,0 1-5 min. 1-5 min. 1-5 min. ::o--60 20 20 Sortmedium wet Soft-- medium wet Medium Medium fine Fine Propellent S olvent Water Ratio--40 20 40 0 100 !5-30 min. V ery wet 15 '85 15-30 min. Medium wet 40 60 5- 43 100 0 15-30 min. >1 hr. >1 hr. Medium Medium Medium fine 2 parts Emcol 14/102 parts finished emulsion The effect of varying the "12"/"114" ratio upon emulsion stability and spray characteristics is indicated by the data in Tabl 5. Data were obtained for propellent/ solvent/water ratios of 60/20/20 and 40/20/40. Propellent " 12"/Propellent " 11"/Solvent/V/ater Emulsions The "12"/"H'7odcrless mineral spirits, water combinations provide nonfoaming sprays with relatively good emulsion stability. As in the previous case with the "12"/' "11"/water emulsions, the spray characteristics of the present type may be varied con siderably by varying the ratio of "12" to "11." Spray characteristics and separation times of a series of this type are given in Table 6. At a given "12"/"11" ratio, the spray characteristics of the emulsion may be varied by varying the concentration of the propellent. This appears to have a greater effect than keeping the concentration of the propellent constant and varying the solvent, water ratio. Data for a series of "12"/''ll" (30, 70), odorless minerals spirits'emulsions are given in Table 7. Table 6--Propellents "12", "11" Odor less Mineral Spirits Water Emulsion Propellent s "12" "ir Ratio, Wt. c-c Separation Times, Min. Spray Charac teristics Propellent Solvent, W dter Rut:\o--o0 20 20 100/0 /0/ 30 50/50 30,'"0 0/100 1-5 30-60 30-t>0 30-60 Fine Medium fine Medium Wet Stream 2 parts Emcol 14/102 parts hnished emulsion Table---Propellents '`12" "'ll" 3<> -0) Odorless Mineral Spirits Water Emul sions , Propeller.: Solvent W'ater Ratio Separation Time, Mm. Scrav Charac teristics oO 10 30 60-15 '25 oO 20 '20 40 '20,'40 2010/60 60'30/10 40/30/30 50-40/10 30-60 30-o0 30- o0 30-o0 30-60 30-60 30-60 Medium wet Medium wet Medium wet Partial stream Stream Medium wet Stream Stream 2 parts Emcol 14 102 parts finished emulsion 3 EID11616 C Eiiecl of Ethyl Alcohol upon Emulsion Stability. The water-in-oil emulsion systems can tolerate a fair'y high concentration of alcohol in the aqueous phase without an aporeciable effect upon emulsion creaming time. The effect of the alcohol was determined with "12" "11" <3C 70; odorless mineral spirits water systems emulsified with Emcol 14. Concentrations of ethyl alcohol ir. the aqueous phase up to 30 per cent had no effect upon emulsion stability. Higher concentrations, however, caused a definite decrease in emulsion stability. Effect of Sodium Chloride upon Emulsion Stability The effect of sodium chloride in the aqueous phase at concentrations of 10 and 25 per cent was evaluated in various emulsion systems containing odorless mineral spirits as the auxiliary solvent. The emulsion creaming time was decreased in all cases, although it was still sufficient for most purposes. The emulsions containing the sodium chloride were considerably less milky than the corresponding emulsions without sodium chloride. The sodium chloride appeared to affect the ease of dispersion of the water rather than the strength of the interfacial film. The creamed aqueous layers appeared visually, at least, to be stable without an observable coalescence of water drops. Viscosity of the M'ater-in-Oil Emulsions and Phase Changes The viscosity of the water-in-oil emulsions is a function of the concentration and type of auxiliary solvents, concentration of propellents, aqueous phase, and emulsifying agent As would be expected, the viscosity of the emulsions increases as the portion of the dispersed aqueous phase increases. Electrical conductivity measurements indicate the emulsions to be of the water-in-oil type. Likewise, creaming occurs from the bottom as would be expected with a water-in-oil emulsion where the dispersed aqueous phase is less dense than the continuous phase and rises to the top. Essentially no foaming occurs when the bottles are shaken. As the viscosity of the emulsions increases the seoaration times become greater as a result of the increased difficulty of movement of the dispersed water droplets. As the concentration of the aqueous phase is increased to 60-30 per cent, in version of the emulsion from water-in-oil to oil-in-water generally occurs. After inversion the viscosity of the emulsions decreases with a corresponding decrease in separation time. Electrical conductivity measurements indicate the emulsions to be of the oil-in-water type and creaming now occurs from the top with the denser dispersed propellent phase settling to the bottom. The oil-in-water emulsions foam considerably when shaken, in contrast to the water-in-oil emulsions. Where the previous water-in-oil emulsions gave a nonfoaming spray, the oil-in-water emulsions produce a stream that foams on contact. These results appear to be similar to those obtained by Sherman (9), who noted that the viscosities of water-in-oil emulsions prepared with distilled water in mineral oil reached a maximum value between 77 and 82 per cent water. At higher concentra tions of water, inversion of the emulsion occurred. The concentration at which inversion occurred was a function of the amount of emulsifying agent present. 9 EID11617 Occasionally it was observed that of two supposedly duplicate samples prepared with 20 per cent propellent and 80 per cent wate-, one was a very viscous water-in-oil emulsion /.'Pile the other sample was the less viscous oii-in-water type. The separation time of the former was generally greater than an nour with creaming occurring from the octtom wr/e the separation time o{ the latter was less than a minute with creaming o:siir-mg :rom tne top. This was probably a case of the formation of dual emulsions emulsions with the same liauids and emulsifying agents but having opposite phase tyoes1 flC,, wnere the type of emulsion that was obtained depended upon how the bottle was shaken. This phenomenon, where the phase type of the emulsion is determined by the type o; agitation, was first observed by Ostwald (11) and later confirmed by Cheesman anc King (1Z;. The electrical conductivity of the emulsions was found generally to be a reliable wears for aetermining the phase of the propellent, water emulsions. In most of the cases investigated the water-in-oil emulsions were essentially nonconducting as the in version point was approached and became conducting after inversion had occurred, however, with "12"/"11" (30. 70)/water emulsions, it was observed that the emulsion containing 40 per cent propellent and 60 per cent water exhibited an electrical con ductance intermediate between that of the nonconducting emulsions with 60 per cent propellent 40 per cent water and the conducting 20/80 emulsion. It is possible that in cases cf this type, application of the electric current caused partial inversion of the water-in-oi! emulsion to take place. This effect with water-in-oil systems has been reported by Dixon and Bennet-Ciark (13). Particle Size of Emulsion Sprays At the present time, very little information on the particle size of the emulsion sprays is available. Attempts to determine the oarticle size of the emulsions at the "Freon" Products Laboratory by the standard technique involving the rotating slide and wind tunnel (14) have not been successful as yet. In the cases studied, the water evaporateo before the droplets reached the slide. In the water-in-oil propellent, water emulsions, the particle size of the sprays is probably controlled to a consioerable extent by the degree of dispersion of the w3ter droplets in the propellent. If this is true, the particle size from a given formu lation will depend upon the method and efficiency of emulsification. An additional factor probably should be considered and that is the effect upon the emulsion stability resulting from the passage of the emulsion through a valve. In the emulsions containing a high proportion of water, the droplets are close together, it appears likely that during the violent agitation occurring in the emulsions during the passage through the valve and immediately following their exit from the outer orifice, considerably more coalescence of the water droplets would occur with the concentrated emulsions than with the dilute emulsions. If this happens, then the particle size of the sprays from the concentrated emulsions will be much larger than those from the dilute emulsions regardless of the fact that the size of the dispersed water droplets was the same in both emulsions before spraying. 10 The picture becomes even more complicated in emulsions formulated with an auxiliary solvent, such as odorless mineral spirits. In this case the propellent is dissolved in the solvent and the flashing of the propellent during spraying breaks the solvent into fine particles. The particle size of the sprayed solvent will depend there fore upon the ratio of propellent to solvent, as in any homogeneous system. What effect the break-up of the solvent has upon the dispersed water droplets is not known, it is possible that the auxiliary solvent and water are sprayed as separate droplets. How ever, if this occurs, then re-emulsification occurs,when the two phases impinge upon a surface. Experiments show that an emulsion is obtained when a propellent, solvent, water emulsion is sprayea into a container. Corrosion Studies with H ater-in-OH Emulsions The combination of water and surface-active agents in aerosol systems always introduces the possibility of corrosion of metal containers. The difficulties that have been encountered in attempts to package aerosol shampoos based on- fatty alcohol sulfates are well known. On the other hand, aerosol shave lathers based on fatty acid soaps have an excellent record with respect to corrosion. The basic water-in-oil emulsion systems discussed in the present report appear generally to have remarkable stability as far as corrosion of metal containers is con cerned. The emulsions were packaged in the following containers for the specified storage temperatures and times: 1. Crown lacquer-lined tin-plate cans equipped with Precision nylon-brass valves Aging periods: 2 months at 130F 1 year at room temperature 2. Continental tin-plate cans equipped with Precision nylon-brass valves Aging periods: 6 months at 100F 1 year at room temperature The particular emulsion systems that were evaluated were as follows: 1. Propellent "12" deodorized kerosene,/water-60 20 20 ratio 2. Propellents "12" "114" (15 85)/"Nujol", water-60.'20/20 ratio 3. Propellents "12" "11" (30 70).- "Nujol"/water-60 20 '20 ratio 4. Propellents "12" "11" (30/70)/water-80, 20 and 60. 40 ratios The first three emulsions systems produced no observable corrosion in any of the containers under any of the storage conditions. The fourth system, "12" "11"/ water emulsions, caused no corrosion in the lacquer-lined containers under any of the storage conditions nor did they cause corrosion in the tin-plate containers at room temperature. After six months of 100F( however, slight detinning on the can shoulders was observed. The general lack of corrosion observed with the emulsion systems is encouraging. It should be recognized, however, that the addition of active ingredients may introduce corrosive characteristics into the system. It is necessary, therefore, to shelf test any practical formulations. 11 EID11619 It has been Droposed by Boe (15) that the water-in-oil systems would be expected to show less corrosion than the oil-in-water systems because in the former, the dispersed water has less tendency to come into contact with the container and valve. Th;s may wc'1 oe an important factor. On the other hand, the surface-active agent that is used aiso ~as an important bearing upon the corrosion that is observed. Some of the other water-ir-oii emulsions prepared with agents other than the Emcol 14 were founo to cause considerable corrosion. Pressures o' Aerosol Formulations The oressures resulting with the propel lent solvent, water emulsions are substantially these of the propellent solvent mixture. The pressures of such mixtures will depend upon the ratio of the mixtures and the particular propellent and solvent that are used. Examples of the pressures of such mixtures are given in Reference 5 anc need not be considered in more detail here. In cases where the proportion of pro pellent is low and the relative proportion of oil-soluble emulsifying agent is high, then the emulsifying agent will contribute to a lowering of the vapor pressure of the propellent Flammabilits These propellents are nonflammable. As a result, all of the propellent/water emulsions are also nonflammable. However, when a flammable auxiliary solvent, such as odorless mineral spirits, is used in the formulation then the flammability properties must be determined. The flammability characteristics of a series of emulsions with varying concen trations of odorless mineral spirits are given in Tables 8 and 9. The propellents were "12" and "12" "11" (30-'70), respectively. The flammability characteristics were evaluated by the flame extension and the flame sustaining tests. The flammability of the formulations appears to be a function of the concen tration of auxiliary solvent, concentration of water, and spray characteristics. The data in Table 3, for example, indicate that emulsions with 20 per cent odorless mineral spirits are nonflammable, those with 30 per cent are flammable but do not sustain a flame, and those with 40 per cent are flammable and sustain a flame. The ratio of propellent to solvent does not appear to be a controlling factor. T^us, as shown in Table 8, "12 odorless mineral spirits water emulsions with 4C 20 40 ratios were nonflammable whereas those with a 60 30, 10 ratio were flammaole. In both cases the propellent solvent ratio is the same. This is also shown in Table 9 where the "12"/"11" (30-70), odorless mineral spirits water emulsion with the composition ratio, of 60, 20 20 was flammable but the emulsion with the lower propellent, solvent ratio of 40 '20 40 was nonflammable. The spray characteristics appear to play a role in determining the flammability of the product. In Table 9, the "12"''"11" (30/70) odorless mineral spirits/water emulsion with the composition ratio of 50/40 10 was nonflammable in spite of the high concentration of solvent. This product had a very wet spray with the standard actuator. On the other hand, the emulsion vA/ith a 60/30 10 ratio was flammable with the lesser concentration of solvent. EID11620 f Changing the valve actuator from a standard actuator to a mechanical break-up type in some cases may shift a product that is flammable by the flame extension test into the nonflammable class by widening the angle of spray. This may also convert a product that does not sustain a flame into one that does, probably by better aeration of the sprayed material. Table 8--Flammability of Propellent ``12"/Odorless Mineral Spirits,'Water Emulsions Propellent OMS Water Ratio -------------- -------------------------- - Flammability ----------------------------------------- - ---- Standard Actuator --------. -----Mechanical Break-up----- . Flame Ext. Flame Sust. Flame Ext. Flame Sust. 60 20/20 XF* XF XF XF 40 20/40 XF XF XF XF 20 '20/60 XF XF XF NF 60 30/10 FL XF NF FL. 40 30/30 FL NF NF FL 20 30/50 FL XF NF NF 50/40/10 FL FL FL FL 40,40/20 FL FL NF FL 20 '40/40 FL NF NF FL 2 parts Emcol 14/102 parts emulsion * NF, nonflammable; FL, flammable. Table 9--Flammability of Propellents " 12"/" 11" (30/70), Odorless Mineral Spirits/Water Emulsions Propellent/ OMS/Water Ratio --------------------------------------------Flammability------------------------------------- ------ ---------- Standard Actuator---------- - -----Mechanical Break-up----- Flame Ext. Flame Sust. Flame Ext. Flame Sust. 60/15 25 XF* XF XF XF 60,20 20 FL XF XF XF 40 '20 40 XF XF XF XF oO 30 10 FL FL XF XF 40 '30 30 XF--Stream XF XF XF 50 40 10 XF--Verv wet XF XF XF 40/40,20 XF--Stream NF XF XF 2 parts Emcol 14 '102 parts emulsion * N F, nonflammable; FL, flammable. Potential Applications oj the Water-in-Oil Emulsions The water-in-oil emulsion systems that have been presented are obviously basic formulations. By the addition of suitable active ingredients, formulations with practical applications will be developed. The active ingredients do not necessarily have to be soluble in the aqueous phase. Organic soluble materials can be dissolved in the auxiliary solvent and water alone added if an emulsion type is desired. Also, organic soluble and water-soluble active ingredients can be combined in the same formulation by dissolving the former in the auxiliary solvent and the latter in the aqueous phase. 13 EID11621 As discussed in the previous sections, the spray characteristics of the emulsion systems car pe varied from very fine to very wet by suitable choice of the emulsion system. This wide range of available spray characteristics provides a variety of potential aoc .cations from topical products, such as antiseptics, antiperspirants, etc., whe'e a wet sorayis desired, to room deodorant and sanitizer sprays, where a fine mist is necessary. In formulating, factors such as the type of container to be used, the pressure of the systems, type of spray, flammability, emulsion stability, and corrosion must all be considered. For many products, such as sun tan sprays, a water-in-oil emulsion system with an auxiliary solvent is particularly desirable since it adheres to the skin and is not readily removed by water. In other cases, where contact of the aqueous phase with the skin is desired, a high boiling organic solvent is not desirable and an emulsion prenared without an auxiliary solvent or with a lower boiling auxiliary sol vent, such as propellent "113" would be preferred. Most of the emulsion sprays, particularly those with axuiliary solvents, do not have an undersirable chilling effect on the skin. This is a considerable advantage for topical applications. In most cases, redispersion of the creamed aqueous layer occurs with ease. In some cases, particularly where the viscosity of the emulsion is high, redispersion takes place in the aerosol container but not in the standpipe. When this occurs, the initial spray consists of an aqueous stream followed by the normal spray. This is undersirable and it is generally necessary to reformulate the product. Of course, if the container is used in an inverted position without a standpipe, the problem does not exist. EXPERIMENTAL Preparation of Emulsions The method of preparation of the various emulsions depended upon the particular propellent and system involved. Water emulsions of "11" or "113" were prepared by dissolving the surface-active agent in this propellent compound, adding the water, and shaking to form the emulsion. As "12" and "114" are gases at room temperature, they must be handled differently. Emulsions of either of the above with water were prepared either by dispersing the agent in the water and pressure loading the propellent solution of the agent The latter is the preferred procedure. Many of the emulsions were formulated with an auxiliary solvent, such as odor less mineral spirits. In such cases, the surface active agent was dissolved in the solvent and the aqueous phase added slowly with agitation. The resulting water-in-oil emulsion was then poured into a coated bottle. If "11" or "113" were used in the formulation, they were added at this time and the bottle was capped. The remainderof the propellent waspressure loaded. After loading was completed, the emulsions were shaken 20 times by hand to complete the dispersion and the separation times were determined within an hour after pressure loading the propellent. 14 EID11622 o Determination oi Emulsion Type Determination of emulsion type was generally carried out with the electrical concuctivity aoparatus described by Griffin (lb). For emulsions uncer pressure the ap paratus was modified by fitting the electric contacts into a glass pressure-tube as discussed in Reference 5. SUMMARY The various methods available for spraying water-based aerosol products are reviewed with emphasis upon the water-in-oil emulsion systems. By suitable choice of propellents anu auxiliary solvents, nonfoaming sprays varying from very fine to very coarse may be obtained. The characteristics and properties of the emulsion systems, such as emulsion stability, flammability, viscosity, stability to electrolytes and alcohol, and particle size of the sprays are discussed. REFERENCES '1; Co I! an s, !_. D., and Griswold, Jr., Chem. Specialties Mfrs. A ssoc. Proc., iird A nn. Meeting, Dec., 1956. (2) Aerosol Age. October (1956), p. 12. (3; Mine. F. A., U. S. Patent No. 2,702,957. (4} Genetron Technicol Data Bulletin WBA-7-56, General Chemicol Co. (5) Technical Bulletin F A- 2 1, 5. l.duPontde Nemour s & Company, Inc. ,6' McCutcheon, J. W., "Synthetic Detergents and Emulsifiers'' (1955). (7) "Atlas Surface Active Agents," Atlas Powder Company `8; Technical Bulletin FA-21, E- ' 4 u Pontde Nemours & Company, Inc. (9; Sherman, P., J. Soc. Chem. Ind., 6 9, S70, S lA ( 1 950}. 10' 2'ay*on, "The Theory of Emu;Sions and Their Technical Treatment," 5th Ed., New York, The 3!akiston Co., Inc. 111 Dstwaid, Wq., Kolloid-Z., 6, 102 f 19 10). 12! Cheesman,D. c.. and King, A., Trans. Faraday Soc., 34, 594 (1938). 13' Dixon, H. rt., and B ennet-CI ar*, T. A., Sature, 124, 650 (1939); Proc. Roy. Dublin Soc.. 19, 422 ! 1930); Ibid.. 20, 211 (1932). 14' Chem. Specialties ,VI/rs. .Assoc. Proc., 43rd Ann. Meeting, Dec., 1956. 15) 3oe, C. F.# 'J. S. Patent No. 2,524590. 16 K ; rk, P. ., and Othmer, 0. F., editors " Encvc loped io ofChemical Technology," Vol. 5, New York, mterscience Ency c. oped i a, Inc. (1950). 17' uormatec hyarocarbon orooe ents used in the preparation of this paper are manufactured under the trade name "Freon" by E. I. du Pont de Nemours and Company, Inc. of Wilmington, Delaware. EID11623 :p FOR FURTHER INFORMATION Please contact one of the following district offices: 60 Glenwood Avenue East Orange, New Jersey 07013 Phone: 676-1112 Area Code 201 7 South Dearborn Street Chicago, Illinois 60603 Phone: 263-7000 Area Code 312 701 Welch Road Palo Alto, California 94304 Phone: 326-2840 (Area Code 415; 712 Main Street Suite 324 Gulf Building Houston, Texas 77002 Phone: 222-2468 Area Code 713) 3503 North Hoyt Street El Monte, California 91734 Phone: 283-0548 CArea Code 213; or: Wilmington, Delaware 19898 Phone: PRospect 4-7963 (Area Code 302) S' The information contained herein is based on technical data and tests which we believe to be reliable and is intended for use by persons having technical skill, at their own discretion and risk. Since conditions of use are outside of Du Pont's control, we can assume no liability for results obtained or damages incurred through the application of the data presented, Publication of the information in this bulletin should not be understood as permission or recommendation for the use of the `'Freon" compounds in violation of any patents. j | j \ J. i PkT.Off Better Things for Better Living ... through Chemistry E. I. DU PONT DE NEMOURS & COMPANY INCORPORATED "Freon" Products Division Wilmington, Delaware 19898 HINTED IN U. S. A. EID11624