212 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS aluminum chlorhydrate (as the model solid), were evaluated at atmospheric pressure relative to their suspension and redispersibility properties in a nonpolar solvent system, which simulated fl•e viscosity of a typical pressur- ized aerosol system. A. Simulated Aerosol Formulation Aluminum chlorhydrate* Fumed silica* Dispersing agent Petroleum ether 5.0 per cent 0.1 per cent 4.9 per cent 90.0 per cent B. Dispersing Agents Isopropyl myristate Propylene glycol monoisostearate Isostearyl isostearate Isopropyl isostearate Propylene glycol dipelargonate C. Preparation of Dispersion The aluminum chlorhydrate, fumed silica, and dispersing agent were mixed together. A 6.0-g sample of this concentrate was then added to a 100-ml grad- uated cylinder, followed by addition of 54.0 g of petroleum ether. The cylin- ders were shaken by hand to give complete dispersion. D. Measuremen,t o/Settling Rate and Ease of Redispersibility The cylinders containing a homogenous dispersion of aluminum chlorhy- drate and fumed silica were allowed to stand, and the volume of clear su- pernatant liquid was measured, starting with a 15-sec time lapse, until settling was completed. The final volume the solid occupied was also recorded. After 24 hours, the number of inversions required to redisperse the powder was measured. These results are shown in Table I. Solubility of Dispersing Agen,t in Propellant The approximate solubility of each of the dispersing agents studied was de- termined by adding a given weight of dispersing agent to an aerosol com- *Chlorhydrol, Impalpable Solid, Micro-dry Reheis Chemical Company, Berkeley Heights, N.J. tCab-O-Sil-M-5, Cabot Corporation, Boston, MA.

SYNTHETIC ESTER DISPERSING AGENTS 213 Table I Settling Rate of Various Dispersing Agents in Petroleum Ether Volume of Supernatant Liquid (ml) Time See Isopropyl Propylene Glycol Isostearyl Isopropyl Propylene Glycol Myristate Monoisostearate a Isostearate ' Isostearate Dipe]argonate 15 11 - -- 26 26 30 36 -- - 51 53 45 56 - -- 73 74 60 74 - - 75 76 75 76 - 77 76 -- 105 77 - -- 77 -- 180 78 -- 77 77 78 900 - 81 -- -- -- Final volume of solids (ml) 8 5 7 8.5 8.5 Number of inversions for redispersion i 2 i I I •Could not measure prior to final settling due to cloudiness of supernatant liquid. patibility tube. The tube was sealed using an aerosol valve, and the appro- priate propellant or propellant blend was added by the pressure process (Pro- pellant 11,* 127 and 114' alone and blended were used). The tube was shaken and placed into a water bath at 25øC -+ 1 ø. After 24 hours, the solu- bility was rated as either soluble (S), insoluble (IN), hazy (H), or slightly hazy (SH). Depending upon the observed result, another tube was prepared using more or less of the dispersing agent more if the previous quantity had been rated soluble and less if it had been rated insoluble. In this manner, the approximate solubility was determined. The results are showm in Table II. Suspension and Redispersion of Solids The •najor objective of this portion of the study was to determine the effect that various dispersing agents have upon the suspension of the powder in an aerosol system. The evaluation was made on the basis of initial dispersibility of the powder, sedimentation rate of the dispersion, and redispersion of the solid after it stood 24 hours and then 1 week. The dispersing agent was added by two methods: by adding it to the liquid portion of the propellant and by dispersing the fluid onto the dry powder. Three powders were dispersed in an aerosol system, which was comprised of mixtures of various dispersing agents, and Propellant 12/11 (50:50). The *Trichloromonofiuoromethane. tDichlorodifiuoromethane. Dichlorotetrafiuoroethane.