MOISTURE MASKS AND CHITOSANS 9 7O o 60 • 50 • 40 o 30 " 20 • 10 0 20 40 60 80 Time (min) Figure 3. Changes of the capacitance increase ratio with time after applying moisture masks containing 2% different molecular weight water-soluble chitosans measured at 20 ø _+ 0.5øC and 75% RH. (MW: ', 2.42 x 106 Da I, 1.62 x 106 Da ', 1.17 x 106 Da O, 2% methyl cellulose, 8.6 x 104 Da). FILM-FORMATION TIME The results in Table VI show film-formation time decreasing from 14.2 to 10.8 min with increasing concentration from 0.5% to 2.0% of U3 chitosan in the moisture mask. This pattern was also true for moisture masks containing lower molecular weight water- soluble chitosans of the same concentration. DISCUSSION VICOSITY OF MOISTURE MASKS The apparent viscosity of moisture masks decreased with increasing shear rate (Figure 1). The results indicate that moisture masks containing water-soluble chitosans were shear- Table VI Effect of Adding Different Molecular Weights and Concentrations of Water-Soluble Chitosans on the Film-Formation Time (min) of Moisture Masks Film formation time Concentration (%) Control U3 chitosan U30 chitosan U120 chitosan 0.5 13.8 b'c 14.2 b 15.4 • 15.6 • 1.0 12.4 a 13.4 c 14.4 b 2.0 10.8 f 11.6 e 11.8 • * a-f values (n = 3) followed by the same superscript are not significantly different (p 0.05 by Duncan's multiple-range test). U3 chitosan, U30 chitosan, and U120 chitosan: the same as in Table I.

10 JOURNAL OF COSMETIC SCIENCE thinning solutions. Table IV shows that the flow behavior indexes (n) are less than 1 for all moisture masks prepared. Results in Table IV confirm the shear-thinning properties of moisture masks shown in Figure 1. The apparent viscosities of moisture masks increased with the increasing concentration of water-soluble chitosans used (of the same molecular weight), or increased with the increasing molecular weight of water-soluble chitosan used (of the same concentration of water-soluble chitosan), as shown in Table III. This may be due to the viscosity of o/w emulsion systems depends on the viscosity of continuous phase that in turn depends on the concentration and/or molecular weight of the polymer used in the continuous phase. Muzzarelli (8) reported that N- carboxymethyl chitosan can increase the viscosity of a solution. The viscosity-increasing capacity is related to the molecular weight of the chitosan. Li (24) reported that water- soluble chitosan obtained by ultrasonic treatment affected the flow consistency index, which increased with increasing molecular weight and concentration of water-soluble chitosans used in the system. Both reports confirm the above results. Moisture masks containing 2% methyl cellulose had a lower viscosity than that containing 0.5% U3 chitosan. This may be because the molecular weight of methyl cellulose is smaller than that of U3 chitosan. The effect of solution pHs between 6.3 and 6.7 on viscosity was not significant. COLOR OF MOISTURE MASKS The results in Figure 2 show the orange-red color of moisture masks increasing with increasing concenration of water-soluble chitosan used in the formula. This may be due to the astacene remaining at the time of chitosan preparation. An increase in the orange-red color of the moisture mask may appeal to consumers because of the warmth associated with this color. EFFECTS ON THE WATER-HOLDING CAPACITY OF MOISTURE MASKS The efficacy of moisture masks in terms of water-holding capacity of the skin was tested by the corneometer method (40-42). The corneometer measures changes of electrical capacitance that are related to the moisture content of the stratum corneum before and after applying a moisture mask. Results in Figure 3 show that after applying moisture masks containing different molecular weight water-soluble chitosans or methyl cellulose (86,000 Da), the electrical capacitance increase ratio increased, then decreased, and finally leveled off. This may be because after applying the moisture mask, the moisture content of the skin increased, and so the electrical capacitance increase ratio increased accordingly. As water evaporated over time, the electrical capacitance increase ratio decreased. Finally, the mask dried out, with the ingredients dissolved in water or the water-alcohol mixture forming a film on the surface of the skin that prevented further water evaporation, and therefore, the electrical capacitance increase ratio leveled off. Electrical capacitance increase ratios were 38%, 34%, 31%, and 26% for those moisture masks containing 2% U3 chitosan, 2% U30 chitosan, 2% U120 chitosan, and 2% methyl cellulose, respectively, after applying those products for 60 min. The results indicate that the water-holding capacity of moisture masks containing different water- soluble chitosans was significantly better than that of masks containing methyl cellulose. This may be due to the fact that either the molecular weight of water-soluble chitosans