Overview [1]

The desiccant can absorb the indefinite amount of moisture in the wet material. There are usually two types: (1) chemical desiccant, absorption of water is accompanied by chemical reaction, such as anhydrous calcium chloride, concentrated sulfuric acid, alkali lime, etc. (2) Physical desiccant, absorb moisture without chemical reaction, such as silica gel absorb moisture in the air. The drying ability of different desiccants is different. The determination method is: firstly, the air saturated with water vapor is passed through the quantitative desiccant at the speed of 1-3l / h at 25 ℃, and then the content of residual water in the air is determined. The less the residual water is, the better the water absorption of desiccant is.

Type and performance [2-3]

Desiccant is a kind of moisture absorbent, which can physically absorb water molecules in its own structure, or chemically absorb water molecules and change its own chemical structure to form another substance. According to their different properties, common desiccants can be divided into three categories: acidic desiccants, such as P2O5, concentrated sulfuric acid, etc.; alkaline desiccants, such as quicklime, NaOH solid, alkali lime, etc.; neutral desiccants, such as anhydrous CaCl2, anhydrous CuSO4, Mg (ClO4) 2, silica gel, molecular sieve, etc.

Silica gel is divided into inorganic silica gel and organic silica gel. Organic silica gel belongs to the special rubber in synthetic rubber, which can be divided into solid and liquid according to its shape, and liquid can be divided into room temperature vulcanization type and high temperature vulcanization type according to its vulcanization temperature. The main component of inorganic silica gel is silica, which is an amorphous machine-made product made of sodium silicate and sulfuric acid in siliceous clay. It is made from natural materials After washing and processing, the mineral becomes granular or bead like, and its structure is very similar to a sponge body. It is composed of interconnected pores, forming a capillary pore adsorption system with huge surface area, which can absorb and preserve water vapor. Under the condition of 100% humidity, it can absorb and condense water vapor equivalent to 40% of its own weight. The main component of silica gel desiccant is silica, which is a kind of highly active adsorption material. It is made of natural minerals and purified into granular or bead shape. As a desiccant, the average pore size of silica gel is 24 angstrom (length unit). It can absorb moisture even when the temperature is higher than 105 ℃. However, when the temperature is higher than 38 ℃, its moisture absorption speed begins to decline. Its optimal moisture absorption state is 21 ℃ ~ 32 ℃. Even when the relative humidity is higher than 60% ~ 90%, it can maintain the relative humidity in the container at 40%. Silica gel has a wide range of packaging materials, such as OPP / PE, PET / PE film, non-woven fabric, composite paper, etc.

Application [2-3]

In daily life, desiccant is widely used in moisture-proof and mildew proof of food, agricultural products, furniture, integrated circuits, precision electronics, leather products, clocks and watches, textiles, books and documents, cultural relics, calligraphy and paintings, containers, auto parts and other products. Usually, we choose the right desiccant, in addition to paying attention to the desiccant can not have any chemical reaction with the material to be dried and its drying performance, we also need to consider the desiccant price economy, convenient operation, safe use and other factors. For example, the commonly used desiccants in the food industry are calcium oxide, silica gel, active mineral desiccant, etc.; when preserving tea, green tea can use block lime without deliquescence, black tea and scented tea can use dry charcoal, and if possible, color changing silica gel can also be used.

1) Desiccant is used to store tea in daily life. The use of desiccant can extend the storage time of tea to about one year. The type of desiccant can be selected according to the type of tea and the convenience of materials. Green tea can be stored with block lime without deliquescence; black tea and scented tea can be stored with dry charcoal; if possible, color changing silica gel can also be used. The color changing silica gel is blue before moisture absorption. When the desiccant particles change from blue to translucent pink, it means that the absorbed water has reached saturation state. At this time, it must be taken out, baked on a low fire or dried in the sun until the original color is restored, and then it can be put into use.

2) Desiccant is used in daily life to preserve drugs. In order to keep the medicine dry or dry the gas, desiccant must be used. There are three kinds of desiccants commonly used: one is acid desiccant, such as concentrated sulfuric acid, phosphorus pentoxide, silica gel, etc.; the second is alkaline desiccant, such as solid caustic soda, lime and alkali lime, etc.; the third is neutral desiccant, such as anhydrous calcium chloride, anhydrous magnesium sulfate, etc. The properties and uses of commonly used desiccants are as follows: concentrated H2SO4 has strong water absorption, which is often used to remove water from the gas that does not react with H2SO4, and is often used as desiccant for H2, O2, Co, SO2 and other gases.

4) Application of desiccant in daily food packaging

The purpose of putting desiccant into food packaging is to reduce the humidity in the food bag and prevent the food from spoilage. Calcium oxide and silica gel are commonly used in food drying. Calcium oxide, also known as quicklime, is a white or grayish white block, which has a strong function of absorbing water in the air. Desiccant is put into food packaging in order to reduce the humidity in food bags and prevent food spoilage. It is most commonly used in children's food packaging. The desiccants in food are generally non-toxic, tasteless, non-contact, corrosive and non polluting; while the desiccants in laboratory, such as concentrated sulfuric acid, alkali lime and so on, are too dangerous, but they also have advantages, such as fast water absorption, high efficiency and low price. live