Formaldehyde aqueous solution, commonly known as formalin, is a colorless transparent liquid with pungent smell. According to the national standard GB / T 9009-2011, the industrial grade is divided into three specifications: 37%, 44% and 50%, and each category has two grades: excellent products and qualified products. It is mainly used as chemical raw materials and preservatives.

1、 Basic feelings

Formaldehyde, chemical formula HCHO or CH2O, formula amount 30.03, also known as formic aldehyde. Colorless gas, pungent smell, irritating to human eyes, nose, etc. The relative density of gas is 1.067 (air = 1), and the density of liquid is 0.815g/cm ³ (-20℃)。 Melting point - 92 ℃, boiling point - 19.5 ℃. Soluble in water and ethanol. The concentration of aqueous solution can reach up to 55%, usually 40%. It is called formaldehyde water, commonly known as formalin. It is a colorless liquid with pungent smell.

2、 Nature

This product is colorless, transparent, volatile and flammable liquid under normal temperature and pressure. It is toxic and irritating. Its steam can form an explosive mixture with air. The explosion limit is 7% ~ 73%. Flocculent precipitation will be precipitated at low temperature. Chemically, it is easy to oxidize to formic acid and polymerize to polyformaldehyde.

It has strong reducing effect, especially in alkaline solution. It can burn, vapor and air form explosive mixture, and the explosion limit is 7% - 73% (volume). The ignition temperature is about 300 ℃.

Formaldehyde can be prepared by dehydrogenation or oxidation of methanol catalyzed by silver, copper and other metals, or separated from hydrocarbon oxidation products. It is used as pesticide and disinfectant, and raw materials for phenolic resin, urea formaldehyde resin, vinylon, urotropine, pentaerythritol and dyes.

Formaldehyde solution of industrial products generally contains 37% formaldehyde and 15% methanol as polymerization inhibitor, with boiling point of 101 ℃.

3、 Use

It is mainly used as chemical raw materials and preservatives. It is widely used in the manufacture of pharmaceuticals, synthetic fibers, synthetic resins, preservatives, urotropine, pentaerythritol, polyformaldehyde, etc.

1. Wood industry: used to produce urea formaldehyde resin and phenolic resin Urea formaldehyde resin is formed by mixing formaldehyde and urea in a certain molar ratio. Formaldehyde and phenol are mixed in a certain molar ratio to produce phenolic resin. The irreplaceable position of formaldehyde in wood processing industry is being replaced by MDI glue.

2. Textile industry: the application of formaldehyde in the textile industry. The use of formaldehyde should be involved in the process of resin finishing of clothing. In the production of clothing fabrics, formaldehyde needs to be added to additives in order to achieve the effects of wrinkle resistance, shrinkage resistance and flame retardancy, or to maintain the durability of printing and dyeing, or to improve the hand feel. Formaldehyde printing and dyeing auxiliaries are mostly pure cotton textiles, because pure cotton textiles are easy to wrinkle. The use of auxiliaries containing formaldehyde can improve the stiffness of cotton cloth. Textiles containing formaldehyde will gradually release free formaldehyde during people's wearing and use, which will cause respiratory tract inflammation and skin inflammation through human respiratory tract and skin contact, and stimulate eyes. Formaldehyde can cause allergies and cancer. Manufacturers use dyeing auxiliaries containing formaldehyde, especially some manufacturers use cheap auxiliaries with high formaldehyde content in order to reduce costs, which is very harmful to human body.

3. Anti corrosion solution: formaldehyde is a substance released by the decomposition of formaldehyde (i.e. sodium bisulfite) above 60 ℃. It is colorless, has a pungent smell and is easily soluble in water. 35% ~ 40% formaldehyde aqueous solution, commonly known as formalin, has antiseptic and bactericidal properties. It can be used to soak biological samples and disinfect seeds. However, due to protein denaturation, the samples are easy to become brittle.

The main reason why formaldehyde has antiseptic and bactericidal properties is that the amino groups on the proteins constituting organisms (including bacteria) can react with formaldehyde.