SINGLE FIBER DEPILATORY STUDIES 469 Appendix to Figure 5 Compositions of Emulsions Used as Treatments in Figure 5 Water-Continuous Oil Continuous Water-Continuous Microemulsion Thioglycolic Acid Water Mineral Oil HLB-2* HLB-6* HLB- 14' Polysorbate 60 Sorbitan Oleate Glycerin 1.72% 38.28% 40.0% 20.0% 1.72% 38.28% 40.0% 10.0% 10.0% __ 1.42% 31.68% 26.5% __ 26.5% 8.6% 5.3% 100% 100% 100% Above systems adjusted to pH 10.5 with NaOH. * Blends of sorbitan and polysorbate esters from Atlab HLB kit © purchased from Chem Service inc. in West Chester, PA. the rate of reduction of hair disulfides was increased when the reducing agent, in their case NaHSO 3, was delivered from W/O microemulsions. As these authors pointed out, there is much more interfacial area in a microemulsion than in a macroemulsion, and 1.0 0.8 0.4 0.2 \ ''-x.•x., x DTG • xx•'•.•DTG + NaCI _ % DTG + MgCI2 '"-. DTG + GuHCI 0.0 I I ....... t ................. • ................. I ................ -] 0 10 20 30 40 50 60 Time (minutes) Figure 6. Effects of salts on stress decay in 0.05 M dithioglutaric acid at pH 10.0. All salts are at an ionic strength of 1.0.

470 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS this may account for the difference in results. We did not investigate W/O microemul- sions. THE EFFECT OF GUANIDINE SALTS ON REDUCTION KINETICS Guanidine salts are known to accelerate the kinetics of hair reduction (8). Figure 6 shows the effect of guanidine hydrochloride (GUHC1), NaCI, and MgC12 at ionic strengths of 1.0 on reduction kinetics using 2,4-dithioglutaric acid (DTG). This dithio-diacid reduces hair very slowly in the absence of salt, probably because its bulk and high negative charge density cause it to diffuse into hair slowly. The addition of NaC1 or MgC12 leads to some increase in reduction rate, but GuHC1 causes a much greater increase at the same ionic strength. This effect is most probably due to a large increase in the rate of diffusion of DTG into the hair as a result of hair swelling induced by GuHC1. The effect of several guanidinium salts on SFTK results with thioglycolate at pH 11.5 are shown in Figure 7. All of the salts reduced T95 % to less than half its original value. Differences between the anions are small and are probably not significant. The major swelling effect seems to come from the guanidinium cation. CENTRAL COMPOSITE STUDY An efficient way to determine effects of multiple parameters is to perform an experi- 1.0 0.8 0.6 0.4 0.2 1-No Salt 2-W/1M GuHCI 3-W/0.5M Su2CO3 4-W/0.5M Su2SO4 5-W/1M GuSCN 4 -"•\\ ,k•" • '" 2 4 6 8 Time (minutes) 0 I 0 10 12 14 Figure 7. Effects of guanidine salts on stress decay in 0.5 M TGA at pH 11.5. 1. No salt. 2. 1.0 M GuHC1. 3. 0.5 M Gu2CO 3. 4. 0.5 M Gu2SO 4. 5. 1.0 M GuSCN.