Document MJXM7KB1qN8wEVbbYGBjbNENk

Lj w A-77 UNUSUAL AQUEOUS AEROSOL FOAMS By Paul Sanders E. I. du Pont de Nemours & Company "Freon" Products Division Wilmington, Delaware 19898 EID11772 Reproduced by permission from AMERICAN PERFUME AND COSMETICS Vol. 84, October 1969 (JL,.-. Mrc Unusual aqueous aerosol foams f By Palx A. Sanders, Freon Products Laboratory, E. I. duPont de Nemours & Company. Wilmington. Del. I n the decade from 1950 to 1960 aerosol foams constituted only a minor proportion of the products on the market; the major foam product was the aerosol shaving lather which appeared in 1950. Dur ing this period most of the products were formu lated to give foams which were quite similar in their appearance and properties. The foams generally were patterned after aerosol shaving lathers and had a comparable stability and density. These foams usually were formulated with 8-10% of a propellant 12/propellant 114 blend, or 3.55.0% of a hydrocarbon propellant. The rest of the (aerosol) formulation generally consisted of an aqueous phase containing various salts of the fatty acids as the major surface active agents, along with other additives. Some of the earlier attempts to formulate aerosol shampoos with the sodium alkyl sulfates were unsuccessful because of container corrosion. Later in the 1960's it was recognized that foam properties could be varied considerably from the somewhat standardized products marketed earlier and foams such as "Crazy Foam.'' a coherent and dry foam designed as a toy for children, the "Sonic" effervescent foams, and various aqueous alcohol foams appeared on the market. Some new and unusual foams to be described in this paper were selected in order to illustrate the variety of foams that can be obtained by changing the proper variables. Although many of the foams discussed have not vet been utilized for the formu lation of commercial products, the variation in prop erties they offer should make them suitable for many different applications in the cosmetic and pharmaceutical fields. Foam compositions and properties Sparkling foam. This product discharges initially as a typical foam with a slightly rough surface. After about 15-30 minutes the surface of the foam starts to disintegrate and appears to be covered wdth snowy crystals, giving the foam a sparkling appear ance. As tlie foam ages it becomes progressively thinner but the sparkling effect remains for at least eight hours. Tne stability of the foam is probably due to complex formation between the triethanol amine myristate and laurvl alcohol. The foam should be useful for displays where long term stability is not necessary'. The addition of fluorescent whitening agents to the foam and the use of ultraviolet light illumination might provide some very striking effects. The composition of the foam is: Laurvl alcohol Myristic acid Triethanolamine Water Propellants 12/114 (40/60) 0.85 wt.% 2.00 1.35 85.80 10.00 The methods for preparing the various foams are given later in this paper. Shiny foam. This product discharges as a dense, almost liquid foam with a very shiny surface. In appearance it is similar to cake icing. The consis tency of the foam is somewhat unusual and has the feel of marshmallow topping. The shiny appearance of the surface disappears after a few minutes. This foam should be suitable for cosmetic and pharmaceutical applications; its composition is: Polvcxyethylene il0. stearyi ither" Cetv. ucohoi Water Propellants 12. 114 140, 60' Atlas Chemical Industries 3.1 wt. ^ l. 1 85.3 10.0 Expanding foam. The foam from this product continues to expand after discharge. It is quite dense and stable for some hours, although the con centration of the surface active agent is relatively low. The stability of the foam results from complex formation between the triethanolamine laurate and laurvl alcohol. The expansion of the foam after discharge is due to the propellant 114 which has a comparatively high boiling point and low vapor pressure. The transition of the propellant after discharge from a liquid to a gas is slower than with the more conven tional. higher pressure foam propellants such as propellant Id propellant 114 140 60'. The pres- EID11773 ent product discharges as a foamy liquid. The addi foam that can be molded or fashioned into various* tion of a vapor pressure depressant to the system shapes such as a ball. The dryness and coherence of would probably give a product which discharges as the foam are due to the high concentration of sur r a liquid and then subsequently expands into a foam. factant and of propellant. Increasing the propel This foam should be useful for pharmaceutical lant concentration1 increases foam stiffness and or cosmetic applications where it is advantageous to decreases foam density. discharge the product into a relatively confined This product is useful for demonstration pur area. Maximum contact for a fairly long period is poses. Its properties are somewhat similar to those subsequendv achieved bv expansion of the liquid of the product Crazy Foam, the tov foam for chil into a foam. The composition of the foam is: dren. The formulation is: Concentrate Par: A launc acid Lauryl alcohol Part B Triethanolamine Water Aerosol formulation Concentrate Propellant 114 2.00 wt. % 1. 66 1.50 94.62 90.00 wt. % 10.00 Collapsing foam. The foam from this product is quite unstable and starts to collapse immediately after discharge. The instability results from the presence of propellant 152a which produces un stable foams in some systems, and the use of the relatively poor foaming agent, triethanolamine laurate. The formulation is: -jncenirate Par: A Laurie no id Part D Triethanolamine Water Aerosol formulation Concentrate Propellant 152a l. 30 96.50 90.00 wt. % 10.00 Periscope foam. This foam has a combination of the properties of both the expanding and collapsing foams. It discharges as a liquid which, immediately expands into a voluminous foam which is stable for only a few minutes and then collapses. An audible hissing noise is evident after the foam has been discharged which is due to the rapid coales cence of the gas bubbles in the foam and subse quent loss of propellant. The liquid discharge and rapid expansion of the liquid to a foam is achieved by the use of a high concentration of propellant 114. The subsequent collapse results from the low concentration of a sur factant which gives comparatively unstable aerosol foams at the concentration at which it is used. The product can be demonstrated effectively by moving the container fairly rapidly as the product is being discharged so that a narrow ribbon of the liquid is deposited. The foam should be useful for cosmetic or pharmaceutical applications when it is desirable to discharge a liquid into a confined area where the foam can expand to achieve maximum contact and then collapse to minimize discomfort. The composition of the product is: Water Tergitol XD* Propellant 11-1 'Jnion Carmce .Corporation 48.0 wt. 1 2.3 30.3 Bouncy warn. Tins foam is a very coherent, drv Concentrate Par' A Stearic acid Ci*cunut tattv Acid Mineral oil Par: 3 Triethanolamine Pulyetnviene glycol 400 Water Aerosol formulation Aqueous concentrate Propellants 12, 114 140/80) 11.05 wt o 77 0.20 9 04 1 84 75. 10 50.00 wt 50.00 Snowflake foam. This foam consists essentially of a basic shaving lather concentrate formulated with a high concentration of propellant. The sample is equipped with a spray actuator instead of a foam actuator. When the sample is sprayed into the air the stream breaks up into snowflakes so that the discharge looks like a heavy snowfall. This product should be useful to simulate snowfalls. The compo sition is: Concentrate Part A Stearic acid Coconut tatty acid Part B Triethanolamine Glycerin Water Aerosol formulation Concentrate Propellants 12 114 1 wt. % 4.4 2.0 64.3 30.0 wt. 70. C Cracklinz foam. The crackling foam is relatively unstable and starts to collapse as soon as it is dis charged. When collapsing, or when rubbed on the skin, the foam makes an audible, crackling sound. One of its unusual features is the very high concen tration of propellant 114 which gives the foam its crackling characteristics. The crackling foam has somewhat similar prop erties to the "Sonic" foams already on the market. This type is suitable for such products as after shaves, skin fresheners, skin moisturizers, etc. The composition is: Water Tergitol XD Propellant 114 10.0 wt.% 1.0 89.0 Methods of preparation 1. Sparkling, shiny foams. These are prepared by mixing together all of the ingredients except the propellant and heating with stirring to about 130140` F. The mixture is then allowed to cool to room temperature with stirring and the resultant concen trate is loaded into containers. .After removal of air by evacuation or purging, the valve is crimped and the propellant is pressure loaded. EID11774 2. Periscope, crackling foams. The water and wet ting agent are stirred together until the surfactant dissolves; heating will increase the rate of solution. The concentrate is loaded into the containers, the samples evacuated or purged, the valve crimped, and the propellant pressure loaded. 1 Expanding, collapsing, bouncy, snowflake foams. In these products the concentrate is divided into two parts, A and B. The concentrate is pre pared by heating Parts A and B separately to about 130-140" F. Part B is then added slowly with gentle stirring to Part A. After the addition is complete the concentrate is allowed to cool to room temperature with stirring. It then is loaded into the aerosol con tainer, the air removed by purging or evacuation, and the propellant pressure loaded. Summary The compositions and properties of eight aqueous foams with unusual properties are given. These foams should he suitable as the basis for a varietv of aerosol cosmetic and pharmaceutical products. It should be recognized that the incorporation of ac tive ingredients and other additives to the foam svstems may change their properties. In addition, be fore any products prepared from these basic systems are marketed, adequate storage stability' tests should be carried out and the patent situation should be investigated. Reference 1. Sanders, P. A,, "Stiffness Measurement of Aerosol Foams." Aerosol Age 8, 23 Juiy, 1963). E. I. DU PONT DE NEMOURS & CO. (INC.) "FREON" PRODUCTS DIVISION WILMINGTON, DELAWARE 19898 FOR FURTHER INFORMATION Please contact one of the following offices: 701 Welch Road Palo Alto, California 94304 Phone: 326-2840 (Area Code 415) Wilmington. Delaware 19898 or Phone: 774-4410 (Area Code 302) i 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 "Freon" compounds in violation of any patents. Better things for better living .. through chemistry 2M or-ntec EID11775 HYik-in*2, A-78 AEROSOL FOAMS By Paul Sanders E. I. du Pont de Nemours & Company "Freon" Products Division Wilmington, Delaware 19898 EID11776 Reproduced by permission from AEROSOL AGE Vol. 14, No. 9 September 1969 i'fir.C 'S' * The first aerosol foam product, shaving lather, ap peared on the market in 1950. It became popular almost immediately, and although manv other aerosol r foam products subsequently were developed and successfully marketed, aerosol shaving lather is still the largest selling aerosol foam product. In 1967. approxi mate!'.' 159 million units were produced in the L nited States, which placed the shaving lathers sixth in vol ume among the various categories of aerosol products reported for that vearh Aerosol foams have been utilized to an increasing extent in recent vears for topical applications. There are a number of reasons for this. In the first place, foams have an aesthetic appeal which cannot be matched bv anv tvpe of spray. In addition, foams can be applied directly to the desired area, without the presentee at me 7m Aeroso1 Congress of the Federation of European Aerosol Associations, June 26, 1965 n Nice, France AEROSOL FOAMS \ By Paul Sanders E. i. duFont dc yemours c- Co Wilmington, Del. the bubbles are called lamellae. The composition of the continuous phase determines the class to which the foam belongs. If the continuous phase is water, the foam, of course, is an aqueous foam. When the continuous phase consists only of organic liquids such as propylene glycol or mineral oil. then nonaqueous foams are produced. A special class of foams known as aqueous alcohol foams is obtained from certain mix tures of water, ethyl alcohol and propellant, where the proportions are such that the components are mu tually soluble. Aerosol foam products are called aerosol foams re gardless of whether it is the aerosol package that is referred to or the product after discharge. However, these products are foams only after discharge. In most cases, aerosol foams are packaged in the con tainer as emulsions, with droplets of the liquefied propellants dispersed throughout the continuous phase. When the product is discharged, the liquefied propellant droplets vaporize and form the gas bub bles of the foam. It can readily be seen that when the foam is obtained from an emulsion system, the foam will, of necessity, inherit many of the characteristics of the parent emulsion. Thus, the interfacial proper ties of the emulsion undoubtedly influence the inter facial properties of the foam. Unfortunately, there have been relatively few basic studies of aerosol emul sions as yet. This is primarily because aerosol emul sions exist only under pressure, and the specialized microscopic equipment required for viewing such emulsions is not vet available. Much of the informa tion about aerosol emulsions has been deduced from the properties of the foams produced by the emul sions. Foam Stability Foams, like emulsions, are inherently unstable. waste or oversprav that often accompanies conven tional spray applications. Also, the foam system pro vides an efficient method for packaging and applying products, since the concentration of propellant gen erally is low and. consequently, the proportion of ac tive ingredient is high. Finally, the properties of foams can be varied over a wide range bv proper formulation techniques to suit different applications. Foams can be obtained which break almost immedi ately after discharge or are stable for weeks. Some foams make a crackling noise when spread, while others are so coherent that they can be molded into There are three major ways in which a foam manifests its instability. These are drainage, rupture of the liq uid films with consequent coalescence of the gas bubbles, and change in bubble size-. A foam drains when the continuous liquid phase settles to the bot tom of the foam. This occurs because of gravitational and capillarv forces acting on the liquid phase3. Drainage causes the liquid films separating the gas bubbles to become thinner, and eventually this can lead to coalescence of the gas bubbles and complete collapse of the foam structure. These processes are illustrated in Figure 1. any desired shape. A foam can be defined simply as a coarse disper sion of a gas in a liquid. In conventional, nonaqueous foams, the dispersed gas usually is air, but in aerosol foams it consists of vaporized propellant. The pro- Drainage Coalascenc* Collapse Figure 1. Stages of Foam Instability pellant may be a fluorinated hydrocarbon such as Another phenomenon that may occur in foams is a V Freon 12 or Freon 114, a hydrocarbon such as iso- change in the size of the dispersed gas bubbles. The butane. or a blend of these propellants. The liquid diameters of the bubbles in anv foam vary consider phase in which the propellant vapor is dispersed is ably and. as the foam ages, the small bubbles become tile continuous phase, and the liquid films separating EID11777 smaller .mil the large Hubbles mav grow larger. This change takes place because the pressure inside a gas bubble in a foam is a function of the diameter of the bubble. The pressure inside a small bubble is greater than the pressure in a larger bubble, and the pressure differential between the bubbles causes the gas mol ecules in the smaller bubbles to diffuse through the liquid films into the larger bubbles. The total pressure. P.. in a gas bubble in a foam is --qua! to atmospheric pressure. Pa. plus a factor. _P. P-. = P. - tlP The magnitude of the factor. 2.P. is determined by the surface tension, v. and the radius of the gas bub ble. R. ', P -- 2y K Therefore, the total pressure inside the gas bubble IS: P, = Pa-2y R It can be seen from the above equation that the pressure inside a bubble with a small radius will be higher than that inside a bubble with a larger radius. Foam Stabilization Foams are unstable by nature, but they can be stabilized by incorporating various additives, such as surface-active agents, into the foam structure. Al though surface-active agents by themselves can be quite effective as foam stabilizers, the molecular com plexes that are formed between surface-active agents and long-chain alcohols or acids generally have a much greater stabilizing effect. Typical examples of combinations that form complexes are sodium lauryl sulfate--laurvl alcohol and triethanolamine stearate--stearyl alcohol. Complexes are also formed between the salts of the fatty acids and free fattv acids. One of the best-known examples of this type is the sodium stearate--stearic acid complex. Recent evidence indicates that complex formation also occurs between the triethanolamine salts of the fatty acids and the free fattv acids.' The complexes function as foam stabilizers in a number of wavs. They increase the viscositv of the system, and this decreases the drainage resulting from gravitational forces. Many complexes form strong, con densed interfacial films around the gas bubbles, and this prevents coalescence of the bubbles, even if they come into contact. In addition, the presence of an interfac-ial film may retard the change in bubble size that occurs during aging. This stabilizing effect results from the lower permeability of the interfacial film to the gas molecules, which decreases the diffusion of the gas molecules from one bubble to another.4 Another stabilizing factor is the repulsion that can occur between gas bubbles with the same electric charge The repulsion results from the presence of electric double '.avers, which form around gas bub bles m a foam through adsorption of a surface-active agent or some other ion at the interface. This is sim ilar to the formation of electric double layers in an emulsion. However, although the repulsion from the electric charge can have a stabilizing effect, the over all importance in foams is probably less than that in emulsions In the usual foam system, formulated with no more than 10*~< propellant, the has bubbles ini tially are too far apart for the repulsive forces to be effective However if drainage takes place, the liquid films separating the bubbles necome thinner, and ulti mate!v the bubbles approach close enough to each other so that a repulsion arises between the hubbies. This tvpe of svstem. where stabilization does not take place until after an initial period of drainage, is re ferred to as a pseudo-stable svstem.4 The fact that drainage occurs at all indicates that the foam is not stable. In systems formulated with very high concentra tions of propellant, i.e., S5-90T. electrical repulsion may be .1 significant factor, however. Even initially the liquid films between the bubbles are very thin and. consequently, stabilization depends mostlv upon electrical repulsion. If such foams are mechanically disturbed by rubbing or spreading, the bubbles co alesce rapidly and the foam collapses, indicating that the foam has essentially a pseudo-stable structure. f Foam Properties It is desirable to be able to describe foams and characterize them, not only for reference purposes, but also to determine how changes in formulation have affected foam properties. Although there are a number of physical measurements that can be made upon foams, a considerable amount of qualitative in formation can be obtained in a few minutes merely hv discharging the foam onto a paper towel and ob serving it. The rapidity with which the foam wets the towel is an indication of its drainage properties, and the rate at which the foam collapses is another indica tion of its stability. The ease with which a foam may be spread on the hand and the feeling that it leaves may be only qualitative aspects of foam properties, but thev are important because they are the ones that the consumer notices. Various physical measurements can also he carried out with relative ease. Foam density can be obtained bv filling a container of known volume with the foam and determining the weight of the foam. A number of equations for calculating foam density have been published.7 * The following equation was developed bv Becher- simplv from the relationship that density is equal to weight divided by volume. Wa is the weight of the aqueous phase, VVP is the weight of the propellant. VI is the molecular weight of the propellant, and Y,, is the volume of the liquid Phase- \v _ w D = -------- ----------- 22.4(H) VY,, ^ V! ( EID11778 Foam stiffness, or the resistance of a foam to pene The simplest aerosol foam svstem consists of water, tration or deformation, is a function of foam viscosity and can be measured with an instrument such as the surface-active agent, and propellant. A typical aque ous foam formulation is given in Table II. This formu Cherrv-Burrell Curd Tension Meter." Foam stiffness lation produces a rich stable foam that can be used r is measured bv placing a dish filled with foam on a as the starting point for many aerosol products. scale located directly underneath a motor-driven curd knit" The knife is driven into the foam at a constant rate of speed and the resistance of the foam to pene Table U Basic Aqueous Foam System tration by the knife causes the scale platform to de press. This is recorded on the scale dial in grams. A typical shaving lather foam will have a stiffness in the range of 60-100 grams. More sophisticated methods of measuring foam viscositv have been described by Shangraw and Richman.'" file rate of foam drainage can be obtained simply i)\ discharging a known weight of foam into a glass funnel located over a graduate. The amount of liquid w hich collects in the graduate can be measured at Aqueous Concentrate Stearic Acid Coconut Fattv Acid T riethanolamine Water Aerosol Formulation Aaueous Concentrate Freon 12. Freon 114 ( 40 60 , Propellant wt. % 6.3 1.6 5.2 86.9 90.0 10.0 predetermined time intervals. The correlation be tween foam drainage and wetting generally is quite good. The rate of foam collapse can be determined bv discharging the foam onto a paper towel and observ ing it against a background of horizontal lines drawn at intervals. If the original height of the foam is noted immediately after discharge, the foam collapse that occurs during any given aging period can be deter mined from the change in foam height. The type of discharge and also the type of foam can be varied to some extent by using different pro pellants. If a liquid discharge which subsequently ex pands into a foam is desired, Freon 114 alone is used as the propellant. Freon 114 has a relatively high boiling point and, consequently, vaporizes more slowly after discharge than blends containing the lower boil ing Freon 12. Propellants 142b and 152a are used to a limited extent in some formulations where their low ,.r*\ EID11779 Aqueous Foams Aqueous foams constitute the largest group of foam products on the market at the present time and will continue to dominate the foam market in the foresee able future. Some tvpical aqueous foam products avail able in the l mted States are listed in Table I. er densities and quick-breaking foam properties are desirable. Freon 11 is not used in aqueous foam products, particularly in metal containers, because of its tendency to hydrolyze in aqueous systems with consequent corrosion of the metal containers. Varying the propellant concentration has a marked effect upon foam properties. Increasing the concen Table I Typical Aqueous Foam Products 1. After-Bath Products 2. After-Shaves 3 Colognes 4. Disinfectants 5. Facial Make-up Foams 6. Hand Creams T. Shampoos S. Shaving Lathers 9. Skin Moisturizers 10. Tov Foams tration increases tiie coherence of the foam, and pro pellant concentrations of 30% or more give drv foams. A few years ago. a very coherent foam was marketed with considerable success. This product was de signed as a tov foam for children and could be molded into various shapes. Increasing the propellant concentration even fur ther to about 85-90% produces a foam structure The propellant concentration in aqueous foams c aries from about 3.5% to as high as 89%. depending upon the type of product. In shaving lathers, and in most foam products, the propellant concentration gen erally does not exceed 10% by weight. When aerosol foam products are formulated with the fluorinated hydrocarbon propellants, blends of Freon 12 and Freon 114 are normally used, with the ratio of Freon 12 to Freon 114 being adjusted to produce which consists mostly of gas bubbles with very thin liquid films m between. Since the bubbles are quite close together, the foam is very sensitive to mechani cal shock and when the foam is rubbed or spread, the bubbles coalesce readily with an audible, crackling noise. A line of foam products based upon this prin ciple has already appeared on the market in the United States. The product line includes skin fresh eners, after-shaves, and colognes. the pressure desired. Freon 12/Freon 114 (15/S5) The type of surface-active compound that is present is used commonly for glass-bottle products, and is another factor that determines foam properties. i Freon 12/Freon 114 >,40/60) for products in metal The triethanolamine salts of the fattv acids are used containers. If the aqueous concentrate contains signi commonly, but manv other tvpes of surface-active ficant proportions of a vapor pressure depressant, then agents, including nonionics, are also included in aero propellant blends with corresponding!'' higher vapor sol formulations. The effect of complex formation be pressures mav be used. tween surface-active agents and long-chain alcohols or acids upon such properties as foam drainage, vis cosity and collapse was mentioned previously. In addition, complex formation usually results in a marked decrease in the bubble size of the foam.5 Recent evidence sun-zests that complexes may also form between certain nonionic polyoxyethylene fattyether surface-active agents and long-chain alcohols or acids. Some combinations, such as polyoxyethylene 10 cet'.! ether--cetvl alcohol, exhibit the proper ties of liquid crystals in aqueous solution, and pro duce pearlescent svstems with high consumer appeal. The aerosols are pearlescent in the bottle, but the re sulting foams do not retain the pearlescence.11 The aqueous ethv! alcohol foam system is unique in a number of respects, and for that reason is consid ered separately.1215 The simplest aqueous ethyl al cohol foam is formulated with a combination of water, ethyl alcohol, Freon 12 Freon 114 (40 60) propel lant and a surface-active agent which is usually "Polawax" * A typical formulation is given in Table Composition of a Typical Aqueous Ethyl Alcohol Foam Water Anhydrous ethyl alcohol "Polawax" Freon 12/Freon 114 ( 40/60) Propellant wt % 30.5 56.5 3.0 10.0 "Pnlawax" is an ethoxviated tatty alcohol marketed by Croda, Inc. The proportions of water, alcohol and propellant are adjusted so that the components are mutually sol uble and form a clear solution. The aerosol product, therefore, is not an emulsion and does not need to be shaken immediately before use. Another advantage of the aqueous alcohol foam system is that it contains over 50T ethvl alcohol which has made possible the development of a number of new foam products. Some of these are listed in Table IV. Table IV Some Commercial Aqueous Alcohol Foam Products 1. After-Shaves 2. Colognes 3. Hair Dressings 4. Insect Repellents 5. Skin Moisturizers 6. Sunscreens The aqueous ethyl alcohol foam system can be varied to give either fairly stable foams or quick breaking foams. This is achieved by changing the water/alcohol ratio or the concentration and type of surface-active agent. Different propellants can also affect foam properties, as can the active ingredients that are added. The stability of the aqueous alcohol foams depends upon the presence of solid particles of the surfaceactive agent between the gas bubbles' which prevents coalescence of the bubbles. This situation can occur only if the surface-active agent is essentially insoluble in the aqueous alcohol concentrate. The solubility of the surface-active agent in the concentrate, therefore, is one of the main factors that governs the stability of the aqueous alcohol foams. Increasing the concentration of alcohol beyond a certain point or increasing the temperature will destroy the foaming properties of the aqueous alcohol svstem. The reason for this is that the surface-active agent becomes soluble in the aqueous alcohol concentrate under these conditions. One of the unfortunate properties of the aqueous ethyl alcohol system formulated with "Polawax" as the surface-active agent is that although the system may be crystal clear at room temperature, the "Polawax" will separate from solution if the product is cooled slightly below room temperature. This results in an unattractive package, and for this reason most aqueous alcohol foam products are packaged in opaque glass bottles. f Nonaqueous Foams Thus far, there have been essentially no products on the market based upon the nonaqueous foam systems. To a considerable extent this is because these foams are relatively new. However, these foams have quite unique properties and the future should see a whole series of cosmetic and pharmaceutical products based upon the nonaqueous foam systems. Since these foams do not contain water, they are par ticularly useful for active ingredients that are sensi tive to moisture. The nonaqueous foams can be for mulated either with glycols or mineral oil as the continuous phase.14-15 The composition of a simple, nonaqueous foam based upon propylene glvcol is given in Table V. Table V Vonaqueous Propylene Glycol Foam Propylene Glycol "Polawax" Freon 12,'Freon (40/60) Propellant wt. % ST.O 3.0 10.0 Propvlene glvcol and the propellant are not misci ble and, therefore, the system consists of an emulsion of propellant droplets dispersed in propylene glycol. Propvlene glvcol foams arc stable for weeks, partially because propvlene glycol has a low rate of evapora tion. The propvlene glycol foams are very dense and creamy. The properties of the glycol foams are determined by the tvpe of glvcol. surface-active agent and propel lant that are used. Propylene glvcol is particularly de sirable as a base because it is low in toxicity and gives excellent, stable foams. Many other glycols give good foams. Surfactants other than "Polawax" can also be 11x1*1!. One of the requirements lor a surface-active agent to he effective is that it must bo insoluble in the EID11780 slycoI that is used. The product will not foam if the surface-active agent is soluble in the glycol. The second nonaqueous foam system is formulated with mineral oil as the base. Mineral oil is used in many nonaerosol cosmetic and pharmaceutical prod ucts. and the nonaqueous mineral oil foams should be useful for these types of products. Mineral oil is miscible with the propellants and the mineral oil foam svstem. therefore, differs from the propylene glycol system in this respect since the lat ter is an emulsion system. The composition of a tvpical mineral oil foam is given in Table VI. Table VI Composition of a Mineral Oil Foam Mineral Oil Cetvl Alcohol Stearvl Alcohol Freon 12 Propellant wt. % 81.0 2.0 2.0 15 0 The mineral oil foams are comparatively thin and unstable compared to the glycol foams. The proper ties of the foams depend upon the mineral oil, surfaceactive agent, and propellant that are used. High vis cosity mineral oils generally produce more stable foams than the lower viscosity oils. A variety of sur face-active agents can be used including the poly oxyethylene fatty ethers. Although it is not necessary for the surface-active agent to be insoluble in the solu tion of mineral oil and propellant, the surface-active agent must be insoluble in the mineral oil alone in order to produce a foam. Since the mineral oils are miscible with the propellants, they serve as vapor pressure depressants. Therefore, 10-15% of Freon. 12 alone is used as the propellant in order to provide sufficient pressure. References 1. 1968 Aerosol Market Report, E. I. tin Pont de Nemours & Company, Freon s Products Division, Wilmington. Dela ware 2. Sanders, P. A., "Principles of Aerosol Technology", Van Nostrand Reinhold Co., New York City (In Press 3. Bikerman, J. J.. "Foams: Theory and Industrial Applica tions", Reinhold Publishing Corp-, New York City, 1953 4. Davies, J. T., and Rideal, E. K., "Interfacial Phenomena", 2nd Edition, Academic Press, New York and London, 1963 5. Sanders, P. A., ] Soc. Cosmetic Chemists. IT, 801 '1966' 6. Sanders. P. A., Soap Chem. Specialties, 43, 68, TO July, August 1967) 7. Spitzer, J. G., Reich, I., and Fine, N., U. S. Patent 2,655,480, October 1953 8. Gorman, W. G., and Hall, G. D., Soap Chem. Specialties, 40, 213 (1964) 9. Sanders, P. A., Aerosol Age, 8, 33 (1963) 10. Richman, M. D., and Shangraw, R. F., Aerosol Age, 11, (May - November 1966) 11. Sanders, P. A., J. Soc. Cosmetic Chemists (In Press) 12. Sanders, P. A., Drug 6- Cosmetic Ind., 99, (August and September 1966) 13. Sanders, P. A., Freon Aerosol Report A-75 14. Sanders, P. A., Aerosol Age, 5, 33 (November 1960) 15. Sanders, P. A., Am. Perfumer Cosmetics, 81, 31 (February 1966) EID11781 E. I. DU PONT DE NEMOURS & CO. (INC.) "FREON" PRODUCTS DIVISION WILMINGTON, DELAWARE 19898 FOR FURTHER INFORMATION Please contact one of the following offices: 701 Welch Road Palo Alto, California 94304 Phone: 326-2840 (Area Code 415) Wilmington. Delaware 19898 or Phone: 774-4410 (Area Code 302) The information contained herein is based on technical data and tests which u>e 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 "Freon" compounds in violation of any patents. EID11782 *IC, u s mto" Better things for better living.. through chemistry PRINTED IN U. S. A