EMULSION STABILIZATION BY GUMS 345 Ld -1 -2 -3 o 0.1 0.2 0.3 0.4 XANTHAN GUM CONC. (% W/W) Figure l l. Effect of xanthan gum on sedimentation rate at different emulsifier concentrations at room temperature. [] 0.25%, + 0.5%, O 1.0%. STORAGE AT 45 DEGREES Samples of the emulsions, stored in capped cylindrical vials in an oven at 45 degrees, were monitored to obtain data on phase changes and creaming. No oil separation was observed in emulsions containing 0.25 % emulsifier. Emulsions containing 0.5 % emul- sifier and no polymer creamed rapidly, but no oil was observed at the top. In emulsions containing xanthan gum, a film of oil (too thin to be measured) was observed. The time required for appearance of this oil film was longer the higher the gum concentration. In all of the emulsions containing 1% emulsifier, an oil layer was observed after storage, and several eventually separated into three phases: oil, a surfactant-rich phase of density intermediate between that of the oil and aqueous phases, and an underlying, relatively clear aqueous phase. Some oil separation was also observed in emulsions containing higher emulsifier concentrations. The greater tendency fbr oil to separate as the emulsi- fier concentration was increased is probably related to the decrease in phase inversion temperature with concentration that has been observed in commercial surfactants (21). A typical set of sedimentation curves for emulsions with 1% emulsifier is presented in Figure 14. With many of the emulsions, creaming was extremely rapid and separation

346 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS -1 - -2- 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 POLYMER CONC. (% W/W) Figure 12. Effect of different polymers on sedimentation rate at 1% emulsifier concentration at room temperature. [] xanthan gum, + sodium carboxymethylcellulose, O methylcellulose. occurred within one day after manufacture. In emulsions where creaming was more gradual, it was usually linear with time initially. Only a few data points were available for calculation of the initial sedimentation rates, making these values somewhat ap- proximate. Patterns for the three polymers in emulsions containing 1% emulsifier are shown in Figure 15. The order is the same as that observed at room temperature. Again, xanthan gum was effective at very low concentrations. Carboxymethylcellulose was next in effi- ciency, while methylcellulose was third. INCLUSION OF SODIUM SULFATE Inclusion of sodium sulfate in relatively high concentration reduces hydration of the polyoxyethylene moieties of the surfactants used as emulsifiers. Evidence for this phe- nomenon is provided by cloud point data (22). The decrease in hydration due to addi- tion of salts or increase of storage temperature is equivalent to decreasing emulsifier HLB.