'218 JOUBNAL OF THE SOCIETY OF COSMETIC CHEMISTS With respect both to the final volume of the solid phase and the redispersi- bility, only the propylene glycol monoisostearate showed a significantly differ- ent performance. This sample was harder to redisperse and had a smaller final solids volume than the others tested. The results obtained, when petroleum ether was used, compare favorably to the results obtained for these dispersing agents in similar tests, but in an ac- tual pressurized aerosol system. The propylene glycol monoisostearate is the only agent studied with any functional group present other than an ester moiety. In this substance, the free hydroxyl group may slow the settling of the aluminum chlorhydrate as a result of its potential for hydrogen bonding. Once the aluminum chlorhydrate particles are coated, the hydrogen bonding may allow tighter packing and a stronger surface film as suggested by the observed smaller solids volume and increased difficulty in redispersibility. In general, the dispersing agents, which are more capable of strong intermolecular attrac- tions allow a slower settling rate, but on the other hand, may cause redisper- sion to be more difficult. The above results suggest that the method described here may be used as a preliminary screening test for potential dispersing agents for aerosol systems •xith respect to settling rate and redispersibility of aluminum chlorhydrate. More subtle evaluations must be carried out in an actual aerosol system in order to establish definitely the usefulness of the method. It can be noted from Table II that isopropyl isostearate, propylene glycoi monoisostearate, propylene glycol monoisostearate (90 per cent), and 2-ethyl- hexylpelargonate are soluble in all propellants studied. As can be predicted, Propellant 11 was the best solvent for most of the dispersing agents, while Propellant 114 was noted to be a poor solvent. This result was not unexpected because of the large number of fluorine atoms present in the Propellant 114 molecule. As can also be noted from Table II, the presence of Propellant 11 in a propellant blend will tend to increase the solubility of the dispersing agent in the other propellants. Propylene glycol monoisostearate and the propylene glycol monoisostearate (90 per cent) consistently showed enhanced suspending properties when used with aluminum chlorhydrate, starch, and talcum. None of the materials used to suspend talcum were very effective. However, this effect is not sur- prising, since talcum has a fairly high density and is difficult to suspend. The fact that powders, which were suspended with propylene glycol monoisostear- ate as the dispensing agent, consistently showed a slower settling rate in aero- sol systems, than did some of the other materials included in this study, con- firms the results obtained when these mixtures were placed in the presence of petroleum ether in a nonaerosol system. Furthermore, this material showed complete solubqity in the propellant systems. Isopropyl isostearate also showed a slower settling rate than d d some of the other materials included in this study, although the differences were not as great as those noted with the

SYNTHETIC ESTER DISPERSING AGENTS 219 propylene gylcol monoisostearates. It can also be noted that little, ff any, dif- ference existed with regard to the usefulness of the isopropyl isostearate or propylene glycol monoisostearates as suspending agents for the other mate- rials studied. It is also interesting to note, that when comparing the settling rate of the solids used in this study in the presence of various dispersing agents, propyl- ene glycol dipleargonate was the least effective because the powders settled rapidly in the presence of th!s material. This material also showed the least solubility in the propellants. All of the samples showed a rather rapid rate of settling. In all cases, some settling occurred immediately with complete set- tling taking place in 4 to 5 min. Isopropyl myristate with aluminum chlorhy- droxide did not show settling for the first 15 sec, as is shown in Fig. 2. Very little difference was noted between the reading taken at the 5 min and 24- hour time intervals. The results shown should be considered to be relative and of help in comparing the usefulness of the various dispersing agents studied, but not as absolute values. Tables III and IV indicate the relative ease of redispersion of the solids using different esters. However, it is necessary to consider both rate of sedi- mentation and ease of redispersion when selecting a dispersing agent. It should be indicated that no anticaking agent, such at fumed silica was to be used in this part of the study. While the number of inversions required to effect redispersion would be different in the presence of an anticaking agent, it is believed that the relative order of usefulness of the esters would be the same. SVMM,•RY and Co•c•,vsIo•s A study was made to determine the effectiveness of various dispersing agents, when they were used as suspending agents in the presence of alumin- um chlorhydrate, starch, and talcum. The solubility of each of the dispersing agents in Propellants 11, 12, and 114 was also determined. A nonaerosol sys- tem, which was useful in screening various dispersing agents, was devised. Two methods of adding the dispersing agent to powder were studied and in- cluded addition of the dispersing agent directly to the propellant phase, as well as direct addition to the powder. Of all the dispersing a•ents studied. vropvlene glycol monoisostearate (and the 90 per cent monoester) were found to be the most effective suspending agents for aluminum chlorhydrate, starch, and talcum. Very little difference was noted among the other dispersing agents used in this study. (Received September 2, 1975) REFERENCES (1) A. Herska, Powder aerosols, I. Soc. Cosmet. Chem., 21, 553 (1970). (2) S.C. Elvin, Powder aerosols, Aerosol Age, 16, 26 (1971). (3) A.M. Rubino, Current Trends in aerosol antiperspirants, Amer. Per[urn. Cosmet., 86, 51 (1971).