144 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 65 60 55 50- 45 - 40 - 35- 5 pbw GMS 10 pbw GMS I i I I I 0 5 10 15 20 25 TIME, MIN. Figure 5. Cooling curves for glycerol monostearate (MP = 55-58øC)--volatile silicone--stearyl alcohol. monostearate also produced unusual sticks. At 5 pbw, syneresis was excessive with liquid silicone collecting in the bottom of the cartridge, but at 10 pbw syneresis was absent and the stick was one of the best in appearance and aesthetics. Stearamide had the highest melting point of all the additives that we investigated and might have been expected to form a step-type cooling curve. The melt had to be heated to a higher temperature than the others and the cooling diagram (Figure 7) is somewhat compressed thereby the curve, however, appears to be a smooth one, indicating co-fusion and a possible solid solution with the stearyl alcohol. C. Casting the Sticks We found that the most uniform sticks can be obtained by fusing under pseudo- equilibrium conditions in a cooling bath set a few degrees below the freezing temperature. This technique minimizes core effects such as shrink holes, cavities, air pockets and surface imperfections. However, since the liquid phase is maintained for a prolonged period by this technique (as compared to forced cooling in an ice bath, for example), settling of the antiperspirant powder becomes a problem. This can be

VOLATILE SILICONES IN ANTIPERSPIRANT STICKS 145 overcome by addition of fairly large amounts of suspending aids, such as fumed silica, or by ultrasonic irradiation of the cooling bath. We found the simplest and most effective means, however, was to stir the equilibrating mixture while it is fusing in the bath for the time indicated by the cooling curve. Shortly before the fusion period has ended, stirring is discontinued and the cartridge is allowed to stand for the final set. This technique produces sticks with excellent uniformity and without core defects. The practical implication of the information accumulated thus far is that, in production, a good way to make suspensoid sticks would be to form the melt in a mixing tank and then drain off excess heat by rapid cooling. As fusion begins, the cooling temperature is set a few degrees below the freezing temperature of the mix and stirring is continued while fusion is allowed to proceed under pseudo-equilibrium conditions. Shortly before fusion is complete, as indicated by the cooling curves, the mix can be pumped into cartridges for the final set. The fusion temperatures and times for the systems studies are summarized in Table II. The data are taken from the cooling curves (Figures 3-7), with the fusion times being calculated as described above. Using these data with the equilibrium fusion technique, fully formulated sticks were cast with the additives listed above and physical properties determined on them as described below. 65 60 55 50 45 40 - 35 - 10 pbw 5 pbw 3O I I I i I 0 5 10 15 20 25 TIME, MIN. Figure 6. Cooling curves for PEG 6000 distearate (MP = 55øC)--volatile silicone--stearyl alcohol.