EMULSION STABILIZATION BY GUMS 347 1.5 1 0.5 -0.5 -1 0 --2 I I I I I I I I I I I I 0.8 1.2 1.6 2 2.4 2.8 ,3.2 LOG VISCOSITY (CP) Figure 13. Relationship between sedimentation rate and apparent viscosity at 1% (w/w) emulsifier con- centration. [] xanthan gum, + CMC, O MC. Figure 16 shows the room temperature sedimentation pattern of emulsions containing 0.2% xanthan gum in the presence of various concentrations of sodium sulfate. With O. 1 M salt present, the creaming rate was increased to a value substantially greater than that observed in the absence of added salt. Further increases in salt concentration caused a change in the creaming pattern and resulted in much more rapid emulsion separation. In emulsions containing 0.2 or 0.3 M sodium sulfate and no polymer stored at room temperature, separation of a thin layer of oil at the top was noted after storage for about 5 months a measurable oil separation occurred after about 9% months. Similar obser- vations were made for emulsions containing O. 1% xanthan gum. No oil was evident in emulsions containing higher xanthan gum concentrations during storage for 10 months. In emulsions containing sodium carboxymethylcellulose and 0.2 M sodium sulfate, an oil film was evident after about 6 months at polymer concentrations of O. 5 and 1.0%. At 45 degrees, the dehydrating effects of temperature and salt were combined. At this temperature, emulsions containing sodium sulfate eventually separated into two phases, oil and a clear underlying aqueous phase. In general, at any given salt concentration, the onset of oil separation was inversely related to the concentration of polymer present in the formulation.

11o (/1 T Q_ z o 100 4 90- 80- 70- 60- 50- 40- 30 20 10 A X 0 IA O0 O0 0 0 A 0 20 40 60 80 100 120 TIME (DAYS) 140 Figure 14. Sedimentation curves at 45øC. Emulsions contained 1% emulsifier and various xanthan gum concentrations. [] 0%, + 0.1%, O 0.2%, A 0.3%, x 0.4%. 2,5 -- - 2- o 1 - 0.5 - -0.5 -1 + o 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 POLYMER CONC. (% W/W) Figure 15. Effect of different polymers on creaming rate at 1% emulsifier concentration at 45øC. [] xanthan gum, d- sodium carboxymethylcellulose, O methylcellulose.