16 JOURNAL OF COSMETIC SCIENCE 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 Time (rain) Figure 4. Changes of capacitance increase ratio with time after applying moisture mask containing different types and concentrations of thickening agents measured at 23 ø + 0.5øC, RH 68.5%. HEC: hydroxyethyl cellulose. MC: methyl cellulose. Extract: Monostroma nitidium aqueous extract. •, 2.0% HEC + 5% humectant. [•, 2.0% MC + 5% humectant. /N, 1.0% HEC + 1.0% extract. C), 1.0% MC + 1.0% extract. Table III Film Formation Time, pH, and Draize Scores of Moisture Masks Containing Different Types and Concentrations of Thickening Agents Measured at 23 ø _+ 0.5øC, RH 68.5% Film-formation time (min) pH Draize score 2.0% HEC + 5.0% humectant 2.0% MC + 5.0% humectant 1.0% HEC + 1.0% extract 1.0% MC + 1.0% extract 1.0% HEC + 2.0% extract 1.0% HEC + 1.5% extract 1.0% HEC + 0.5% extract 1.0% HEC + 0.25% extract 12.66 6.61 0 13.16 6.54 0 13.08 7.39 0 13.25 7.30 0 12.05 7.50 0 12.42 0 13.50 7.26 0 14.08 7.05 0 HEC, MC, and extract are the same in Table II. moisture masks ranged between 6.54 and 7.50 and were slightly higher than the normal pH of human skin. STORAGE STABILITY Changes in the apparent viscosity of moisture masks during storage at 4øC were used as an index of storage stability. Results in Figure 5 show that the apparent viscosity of

WATER-SOLUBLE MUCILAGE IN A MOISTURE MASK 17 3500 3000 • 2500 o 2000 .•--• • 15oo :• lOOO 500 o o e____e 0 2 4 6 8 lO 12 14 16 Weeks Figure 5. Changes in apparent viscosity of moisture masks containing different types and concentrations of thickening agents over time at 4øC. Apparent viscosity was measured at 25 ø + 0.2øC with a shear rate of 100 1/s for 3 min. HEC: hydroxyethyl cellulose. MC: methyl cellulose. Extract: &lonostroma nitidiam aqueous extract. ', 2% HEC + 5% humectant. l, 1% HEC + 1% extract. /•, 2% MC + 5% humectant. O, 1% MC + 1% extract. moisture masks containing different types and concentrations of thickening agents, with or without 5% humectant, decreased over time at 4øC. Moisture masks containing HEC remained relatively stable for six weeks, and then the apparent viscosity began to decrease and level off at the eighth week, whereas in a moisture mask containing MC, the apparent viscosity started to decrease from the beginning and leveled off at the fourth or sixth week. DISCUSSION VISCOSITY OF MOISTURE MASKS Results in Table II show that the flow behavior indexes (n) are less than 1 for all moisture masks prepared. This indicates that moisture masks are shear-thinning solutions. This may be due to rotational Brownian movement of the molecules in low shear rates. However, they tend to align with the stream line of the flow with increasing shear rate, thus decreasing the resistance of the flow. Therefore, the apparent viscosity decreased (12-14). For those moisture masks containing thickening agents of HEC, MC, or mucilage, the viscosity increased with increasing concentration of HEC, MC, or muci- lage, as shown in Table II. This may be due to the viscosity of o/w emulsion systems,