Chapter 5 187 These data show the effect of pH on depilation time. We also investigated many other factors, including the effect of oxidative pretreatment, which reduces depilation time, and several solvents. At 20% concentration, ethanol and acetone had little or no effect, while n-propanol, triacetin, glycerin, and propylene glycol all increased T 95 . We formulated oil-in-water (o/w) and water-in-oil (w/o) emulsions with 40% mineral oil and a microemulsion with 26.5% mineral oil and 1.7% NaTGA at pH 10.5 and compared them to both 1.7% NaTGA and 4.3% NaTGA (the concentration in the water phase) to investigate the effect of emulsion type on reduction rate. Results are shown in Figure 19. Interestingly the reaction with the o/w emulsion (Figure 19, curve 5) was as fast as with thioglycolate in water at the concentration in the water phase (the formulations were 38% water). Reduction was very slow with the w/o emulsion. It is likely that the oil phase coats the hair and prevents the reducing agent from diffusing in. Breuer reviewed depilatories and measurement methods Figure 19 Effect of emulsion type on reduction kinetics. 1. W/O emulsion 1.72% TG 2. Solution 1.72% TG 3. Microemulsion 1.72% TG 4. Solution 4.3% TG 5. o/w emulsion 1.72% TG, 4.3% in water phase. For formulation details. see Wickett and Mermelstein.31