The melting point of formaldehyde is -92 °C, the boiling point is -21 °C, the density in liquid state is 0.815 g/3 cm (20 °C), it is easily soluble in water and ethanol, and the 35~40% aqueous formaldehyde solution is called formalin. There are aldehyde groups in formaldehyde molecules
Polycondensation reaction to obtain phenolic resin (Bakelite):
Formaldehyde is an important organic raw material, mainly used in the plastic industry (such as phenolic resin, urea-formaldehyde plastic-electrojade), synthetic fibers (such as synthetic vinylene-polyvinyl alcohol formaldehyde), leather industry, medicine, dyes, etc. Forma wood has the ability to kill and preserve, can be leached into biological specimens, and its dilute solution (0.1-0.5%) can be used in agriculture to soak seeds and disinfect seeds. Commonly used catalytic oxidation methods in industry to produce formaldehyde from methanol:
The properties of formaldehyde, its harm to the human body and its source
&Nbsp; Formaldehyde is a colorless, strong odor irritating gas, and its 35%~40% aqueous solution is commonly known as formalin. Formaldehyde is a purore poison, which can bind to proteins, and after inhaling high concentrations of formaldehyde, severe irritation and edema of the respiratory tract, eye tingling, headache, and bronchial asthma can also occur. Direct contact with formaldehyde on the skin can cause dermatitis, pigmentation, and necrosis. Frequent inhalation of a small amount of formaldehyde can cause chronic poisoning, mucosal congestion, skin irritation, allergic dermatitis, nail keratinization and fragility, pain in the fingertips of the nail bed, etc. Systemic symptoms include headache, fatigue, poor stomach pressure, palpitations, insomnia, weight loss, and autonomic nervous disorders.
Various man-made panels (particleboard, fiberboard, plywood, etc.) can contain formaldehyde due to the use of adhesives. Adhesives are used in the production of new furniture, wall and floor decoration. Wherever adhesives are used in large quantities, there will always be formaldehyde release. In addition, some chemical fiber carpets and paints also contain a certain amount of formaldehyde. Formaldehyde can also come from cosmetics. Cosmetics, detergents, insecticides, disinfectants, preservatives, printing inks, paper, textile fibers and other chemical and light industry products.
Uses of formaldehyde
Formaldehyde is a bulk chemical product with a wide range of uses, simple production process and sufficient supply of raw materials, and is the backbone of the downstream product tree of methanol, with an annual output of about 25 million tons in the world, and about 30% of methanol is used to produce formaldehyde. However, formaldehyde is a low-concentration aqueous solution, which is not convenient for long-distance transportation from an economic point of view, so factories are generally set up near the main consumer market, and import and export trade is very rare. In addition to being directly used as a disinfection, sterilization, and preservative, formaldehyde is mainly used in organic synthesis, synthetic materials, coatings, rubber, pesticides and other industries, and its derivative products are mainly polyoxymethylene, polyoxymethylene, phenolic esters, urea-formaldehyde esters, amino esters, urotos products and polyols. The wood-based panel industry is developed, and the demand for formaldehyde is very large.
Formaldehyde is used in a wide range of applications, synthetic resins, surfactants, plastics, rubber, leather, papermaking, dyes, pharmaceuticals, pesticides, photographic film, explosives, building materials, and disinfection, fumigation and anti-corrosion processes are all used in formaldehyde, it can be said that formaldehyde is an all-rounder in the chemical industry, but the use of anything must have a limit, there is a standard, once the use exceeds the standard and limit, it will bring disadvantages.
According to people familiar with the matter, the price of 1 ton of formaldehyde is around 1,600 yuan, and the main reason for formaldehyde abuse is its low price. Over the past few years, China's formaldehyde production has become a trend of increasing year by year, which is consistent with the development of China's textile industry and building materials industry, which shows that formaldehyde is still the darling of China's chemical industry for a long time to come. According to relevant experts, in recent years, China has successfully developed formaldehyde-free iron-free finishing agents, as well as formaldehyde-free environmentally friendly urea-formaldehyde resins, but they have not been put into production in large quantities to this day, mainly because they are expensive, and it can be seen that cheap prices hinder the replacement process of formaldehyde.
Application of formaldehyde
1) Wood industry
It is used to produce urea-formaldehyde resin and phenolic resin, which is produced by the reaction of formaldehyde and urea mixed according to a certain molar ratio.
2) Textile industry
The use of formaldehyde in the process of resin finishing of clothing must be involved. In the production of clothing fabrics, in order to achieve the effects of anti-wrinkle, anti-shrinkage, flame retardant, etc., or to maintain the durability of printing and dyeing, or to improve the feel, formaldehyde needs to be added to the additive. At present, formaldehyde printing and dyeing additives are more commonly used in pure cotton textiles, because pure cotton textiles are easy to wrinkle, and the use of additives containing formaldehyde can improve the stiffness of cotton fabrics. Textiles containing formaldehyde will gradually release free formaldehyde during people's wearing and use, causing respiratory tract inflammation and skin inflammation through human respiratory tract and skin contact, and will also cause irritation to the eyes. Formaldehyde can cause allergies and can also induce cancer. Manufacturers use dyeing additives containing formaldehyde, especially some manufacturers use cheap additives with extremely high formaldehyde content in order to reduce costs, which is very harmful to the human body.
3) Anti-corrosion solution
Formaldehyde is a substance released by the decomposition of (i.e., sodium bisulfite) above 60 °C, which is colorless, has a pungent odor, and is easily soluble in water. 35%~40% formaldehyde aqueous solution, commonly known as formalin, has antiseptic and sterilization properties, and can be used to impeach biological specimens, disinfect seeds, etc.
The reason why formaldehyde has antiseptic and bactericidal properties is mainly because the amino energy on the proteins that make up organisms (including bacteria) react with formaldehyde.
4) Food industry
Using the preservative properties of formaldehyde, it is added to foods that are not easy to store, such as aquatic products.
3. Harm of formaldehyde to human health
The main health hazards of formaldehyde are as follows:
a. Stimulating effect
Formaldehyde is a propulous toxic substance that can bind to proteins and cause severe irritation and edema of the respiratory tract, eye irritation, and headache when inhaled at high concentrations.
b. Sensitization: Direct skin contact with formaldehyde can cause allergic dermatitis, pigmentation, and necrosis, and inhalation of high concentrations of formaldehyde can induce bronchial asthma.
c. Mutagensis: High concentrations of formaldehyde are also a genotoxic substance. Laboratory animals can cause nasopharyngeal tumors when inhaled at high concentrations in the laboratory.
4. Limitations of formaldehyde on textile printing and dyeing auxiliaries
Zhang Jie has put forward opinions on this issue, which can be summarized as follows:
Textile additives that make textiles in direct contact with the skin exceed 30PPm and all other textiles exceed 300PPm, such as wool protectors, color fixation, cross-linking agents, adhesives, etc. containing excessive formaldehyde amounts.
Limit the amount of free and partially hydrolyzable formaldehyde in textile dyes, and ensure that the amount of free and partially hydrolyzable formaldehyde produced on fabrics cannot exceed 30ppm for textiles in direct contact with the skin, and not more than 300ppm for all other textiles.
Heavy metal salts (except iron) or formaldehyde cannot be used as decolorants or fading agents in textiles.
