The oil-based raw materials used in cosmetics usually include oil, wax, silicone oil and its derivatives, high-grade fatty acids and high-grade fatty alcohols. According to their sources, the oil used in cosmetics can be divided into vegetable oil, animal oil, mineral oil and synthetic oil. The characteristics and quality of oily raw materials can be characterized by the following physical and chemical parameters, according to which the quality of oily raw materials can be determined. At the same time, the physical and chemical properties of oily raw materials are very important to the appearance, stability and use effect of cosmetics.
Physicochemical properties of oily raw materials
1 Viscosity
Viscosity is a measure of resistance to flow of fluids due to intermolecular forces. Oil based raw materials generally have high viscosity, which is caused by the attraction of long chain molecules in oil-based raw materials. Cosmetics industry media network understands that viscosity is a direct factor affecting the spread of cosmetics, but also affects the texture of cosmetics.
2 specific gravity
The specific gravity of oily raw materials is directly proportional to its molecular weight and viscosity, and inversely proportional to its temperature. The smaller the molecular weight or the higher the degree of unsaturation, the greater the specific gravity. The size of specific gravity directly affects the stability of cosmetic products. Generally, oil with similar specific gravity to water is selected.
3 melting point and freezing point
Melting point is the temperature at which a substance changes from a solid to a liquid. The melting point of oily raw materials is not only related to the fermented grains, technology and quality control of products, but also to the seasonal changes of products and other factors. Melting point not only affects the consistency of cosmetics, but also affects the heat and cold stability of products, as well as the spread and skin feeling during use.
Freezing point is the temperature at which a substance changes from liquid to solid. The effect of freezing point of oily raw materials in cosmetics is consistent with the melting point of oil.
4 acid value
The acid value represents the content of free fatty acids in oily raw materials. If animal and vegetable oils are stored for a long time, some free fatty acids will be produced by hydrolysis, so the acid value also indicates the freshness of the oil. The higher the acid value is, the worse the oil is rotten, the less fresh it is, and the worse the quality is. Generally, the acid value of fresh oil is less than 1.
5 iodine value
The iodine value of oil-based raw materials indicates the degree of unsaturation. The higher the iodine value, the greater the degree of unsaturation. Oil with high degree of unsaturation is prone to oxidative rancidity in air. According to the classification of iodine value, the oil can be divided into non dry oil (iodine value & lt; 100), semi dry oil (iodine value & lt; 100), and dry oil (iodine value & gt; 130). The main oils suitable for cosmetics are non dry oil and semi dry oil.
Saponification value and unsaponifiable matter
Saponification value (unit, mgKOH / g) refers to the milligram of potassium hydroxide needed for saponification of 1G oil. The saponification value of fatty acids in oil-based raw materials is small when the molecular weight of fatty acids is large, and vice versa. According to the saponification value, the average molecular weight of oil raw materials can be estimated. The saponification value of general oils is 180 ~ 200.
Unsaponifiable substances refer to the substances that can not react with caustic soda in oil saponification, mainly including macromolecular alcohols, waxes, carbohydrates, pigments, etc.
7 refractive index
Refractive index is caused by the optical path difference of light in two different media, which makes light enter from one medium to another. When its propagation direction is not perpendicular to the interface of the two media, the propagation direction at the interface changes and light refraction occurs. Refractive index is the measurement of light refraction. As a standard for the purity of liquid substances, it is more reliable than boiling point. In the formulation of cosmetics, the combination of oil with different refractive index can improve the appearance effect of emulsion, such as brightness and permeability. When the refractive index of oil phase is consistent with that of water phase, the product can form transparent emulsion. The refractive index of water is 1, and the refractive index of general oil is less than 1. Therefore, propylene glycol, glycerin and butanediol with refractive index greater than 1 can be added to the water phase to achieve the same refractive index of water phase and oil phase, so as to obtain transparent emulsion.
8 hydroxy / acetyl
The hydroxyl value is the milligram number of potassium hydroxide (KOH) equivalent to the hydroxyl in 1g sample, in mgKOH / g. It is usually detected in higher fatty alcohols.
The acetyl value is the number of milligrams needed to neutralize the acetic acid decomposed from 1g acetylated oil with potassium hydroxide, in mgKOH / g. This is usually detected in acetylated fats.
Among the oiliness raw materials, the parameters related to some oilseeds also include ash content, pH value, loss on drying, etc. The above parameters can be used to evaluate the quality of oily raw materials, combined with the skin feeling, and can be formulated to adapt to various uses.
The role of common oily raw materials
Source: Network
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