268 100 90 "'O 80 "'O 70 a, 60 "'O 50 40 C 30 e '#- 20 10 0 0 2 JOURNAL OF COSMETIC SCIENCE 4 y = 6,7266x + 2,8085 R2 = 0,9709 RETI C cone y = 5,9523x + 7,0805 R2 = 0,9613 RETI C 6 8 10 time (days) ♦RETI C ■RETI C cone Figure 3. Percentage of retinol degradation in RETI C and RETI C concentrate emulsions after storage at 40 ° C. 100 90 "C 80 C 70 · 60 a, 50 40 "ii 30 � � 0 20 10 a 0 2 4 6 time (days) 8 10 • RETI C • • • • ·RETI C cone Figure 4. Percentage of weight of RETI C and RETI C concentrate emulsions remaining after storage at 40 ° C. storage at 40 ° C. After one day at 40°C, the decrease in percentage of retinal in RETI C emulsion was 19.8% and the weight loss equal to 0.5%. After three days in the incubator, the retinal concentration decreased by 25.9% compared with initial amount, and the weight loss was at 2 .4 7 % . After a week, the percentage of retinol degraded was 49.8% and the weight loss was 40.8%, while after ten days they were 64.9% and 67.7%, respective! y. The decrease in retinal percentage in RETI C concentrate emulsion was 11.2% after one day, and the weight decreased by 3.5%. After three days at 40 ° C, the retinol showed a decrease of 27.9% in respect to initial concentration, while the weight loss was 14.6%. After a week, the retinal degraded was 42.8% and the emulsion weighed 29.1 % less. Finally, after ten days, the decrease in retinal percentage and the weight loss were 73.4% and 64.3%, respectively.

ANTI-AGING EFFECTIVENESS OF RETINOL EMULSIONS 269 (a) Viscosity. The viscosity of RETI C and RETI C concentrate emulsions was investi­ gated over time after storage at 40°C. For RETI C emulsion, viscosity progressively decreased until the seventh day, but it increased again after ten days. However, RETI C concentrate emulsion showed a different behavior, with viscosity decreasing at first, increasing slightly after seven days of storage, and showing lower values after ten days (Figures 5 and 6). ( b) Rheologic determinations. Flux rheograms of RETI C and RETI C concentrate emulsions after storage at 40 ° C were performed. The curves reported in Figure 7 of RETI C emulsion indicate that the shear stress decreased over time, but the found values were higher after ten days in comparison to those of the seventh day. The thixotropic hys­ teresis area appeared smaller, and the system, initially pseudoplastic, became Newtonian. Figure 8 shows the rheograms of RETI C concentrate emulsion. Also, in this case, the shear stress decreased and the flux changed from pseudoplastic to Newtonian with a reduction of the thixotropic hysteresis area. en §. - · 0 c., · en - 0 c., ·s: 80000 70000 60000 50000 40000 30000 20000 10000 0 0 :lK. .1.., ,:, -�-\.......... - --■ *. - . - - � � :_�:=--: :=: :_ � 5 10 • at opening - • - after 1 day - • - after 3 days - ·E- • after 7 days · - iK- - · after 10 days 15 Figure 5. Viscosity of RETI C emulsion before and after storage at 40 ° C. 80000 70000 60000 • at opening 50000 - • - after 1 day 40000 - • - after 3 days 30000 - ·E- • after 7 days 20000 • - • • · after 10 days 10000 0 a 5 10 15 Figure 6. Viscosity of RETI C concentrate emulsion before and after storage at 40 ° C.