Test method for moisture retention of cosmetics

The moisture in the stratum corneum of the skin is of great significance for maintaining the softness and elasticity of the skin, maintaining the normal metabolism of the skin, and preventing skin aging and wrinkles. The water content of the stratum corneum of healthy skin should be between 10% and 30%. If the water content of the skin is less than 10%, the skin will be dry, rough, and may be chapped. Under normal circumstances, due to the water absorption and barrier function of the stratum corneum, coupled with the covering of lipids secreted by the sweat glands and sebaceous glands, the moisture in the stratum corneum of the skin is not easy to lose. However, in the cold and dry climate, the environmental humidity is low and When the normal barrier function of the skin is damaged, it is easy to cause skin dehydration, which in turn causes the skin to undergo various changes such as dryness and roughness. Moisturizers occupy an extremely important position in cosmetic raw materials for two reasons. First, the quality of cosmetics depends on moisturizers, and second, one of the basic substances that make up cosmetics is also moisturizers. The moisturizer maintains the moisture of the skin and promotes the absorption of moisture, so as to moisturize and moisturize the skin. In the past, people often thought that the following two methods can be taken to prevent skin dehydration. First, use water-soluble water-retaining substances on the skin surface to moisturize the stratum corneum. Second, use fat-soluble substances to form a layer on the skin surface. The protective film prevents the loss of moisture in the stratum corneum of the skin. The skin is filled with proper moisture. A large number of studies have shown that the real cause of dry skin is the lack of water in the stratum corneum. Therefore, if only fat-soluble substances are applied to the surface of the skin, the stratum corneum cannot be hydrated. In recent years, in order to satisfy the moisturizing effect of cosmetics, related research on moisturizers and moisturizing cosmetics has also received increasing attention and attention from the industry. Some scholars believe that an ideal moisturizer should have the following properties: First, it should have continuous and moderate moisture absorption, and the moisture absorption power should not be easily affected by ambient temperature, humidity, etc.; second, the lower the volatility and freezing point, the better , With moderate viscosity, strong skin affinity, and good coexistence with other ingredients; third, it should be as colorless, tasteless, odorless as possible, and safe. There are many commonly used humectants, including polyhydric alcohols, which are the most studied and also the most widely used, followed by betaine, sodium pyrrolidone carboxylate (PCA-Na), mucopolysaccharide-sodium hyaluronate and so on. How to scientifically characterize the moisturizing effect of cosmetics is of great significance to the research and development of cosmetics. At present, the evaluation methods for the moisturizing effect of cosmetics include near-infrared light method, capacitance method, and differential scanning calorimetry (DSC). This test method proposes that there is no accurate reference data, therefore, it is not suitable for the evaluation of the moisturizing effect of cosmetics. A method for testing the moisture retention of cosmetics, the method comprising the following steps: (1) adding magnesium chloride and water to two beakers to prepare a saturated aqueous solution of magnesium chloride, and adding glucose and water to the other beaker to prepare a saturated aqueous solution of glucose; (2) Take a piece of dry filter paper into the drying box to remove moisture, weigh it to obtain the weight of the filter paper Ml, evenly apply the cosmetics to be tested on one side of the filter paper to obtain the filter paper coated with the cosmetics to be tested, and then weigh it to obtain Weight M2; (3) Pour the saturated aqueous glucose solution obtained in step (I) into a dry box, seal it to stabilize the humidity in the dry box, and then apply the cosmetics to be tested obtained in step (2) The side of the filter paper coated with the cosmetics to be tested faces upwards, and covers it on the beaker containing the saturated aqueous solution of magnesium chloride prepared in step (I). At the same time, a piece of dry filter paper with an initial weight of ml is covered on the other portion containing On the beaker of saturated aqueous magnesium chloride solution, put the two beakers on the holder in the drying box, and place them at a constant temperature for 24 hours, then weigh them to obtain the weight M3 of the filter paper coated with the cosmetics to be tested and the weight m2 of the blank filter paper; (4 ) The moisture retention rate of the cosmetic to be tested is [M3-M1-M1X (m2-ml)+m2]+ (M2-M1) X 100%. Preferably, the preparation method of the saturated magnesium chloride aqueous solution in step (I) is as follows: weigh 2-10 g of magnesium chloride and dissolve in 30-100 ml of deionized water, stir and mix well to obtain a saturated magnesium chloride aqueous solution. Preferably, the method for preparing the saturated aqueous glucose solution described in step (I) is as follows: weigh 5-30 g of glucose and dissolve it in 20-200 ml of deionized water, stir and mix to obtain a saturated aqueous glucose solution. Preferably, the amount of the saturated aqueous solution of glucose added in the step (3) is 2 (T200ml. Preferably, the amount of the saturated aqueous solution of magnesium chloride in the beaker containing the saturated aqueous solution of magnesium chloride in the step (3) is 20% to 30% of the total height of the beaker. Preferably, the shape of the filter paper is consistent with the shape of the beaker mouth, and the shape of the filter paper is just enough to completely cover the beaker mouth. Preferably, the criticality of the saturated aqueous solution of magnesium chloride is relatively The humidity (CRH) is 23-33%. Preferably, the critical relative humidity (CRH) of the saturated aqueous glucose solution is 75-90%. Preferably, the temperature range of the constant temperature of the drying box in the step (3) Is 1(T40°C.
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