Industrial formaldehyde (HCHO), as a chemically reactive organic chemical raw material, plays a core role in the plastic manufacturing field as the basic raw material for synthesizing key resins. Through condensation and polymerization reactions with different monomers, it generates plastics and plastic additives with specific properties. Its applications cover various categories such as general plastics and engineering plastics, determining the structure, performance and application scenarios of the final plastic products.
1. Synthesize core resins, construct the basic structure of plastics 
Formaldehyde itself cannot directly form plastics. It needs to react with monomers such as phenol, urea, and melamine to produce resins. These resins are both the core material of plastics and the key carrier for plastic molding. They mainly fall into the following three categories: 
The raw materials for synthesizing phenolic resin (PF) 
Formaldehyde and phenol undergo condensation polymerization under the catalysis of acids or bases to form phenolic resin. This is the earliest synthesized resin to be industrialized and is also an important base material in plastic production. In the early stage of the reaction, a hydroxymethyl phenol intermediate is formed, which then connects through methyl bridges or ether bridges to form low-molecular-weight prepolymer. After being heated and solidified, it forms a three-dimensional cross-linked thermosetting structure, possessing characteristics such as high temperature resistance, strong insulation, high mechanical strength, and resistance to acid and alkali corrosion. 
The phenolic plastic (commonly known as bakelite) made from phenolic resin is widely used to manufacture electrical components such as electrical enclosures, sockets, and switches. It is also used in automotive brake pads, laboratory countertops, billiard tables, and other wear-resistant and high-temperature products. In the casting field, phenolic resin can be mixed with sand to form mold cores, which harden and solidify after heating, meeting the precise processing requirements of industrial castings. 
2. The main components of amino resins (urea-formaldehyde resins, melamine-formaldehyde resins) 
This type of resin is formed by the condensation polymerization of formaldehyde with urea and melamine respectively. It is an important source of plastics and plastic processing additives. The properties of the two are respectively characterized by their own advantages: 
Urea-formaldehyde resin (UF): This resin is formed by the reaction of formaldehyde and urea. It is cost-effective, has a fast curing speed, and has a certain degree of transparency. Besides being used as a bonding agent for artificial boards, it can also be molded into plastic materials, which are utilized in the production of electrical switches, lamp holders, handles for kitchen utensils, toilet covers, and other daily and industrial products. Its drawbacks include poor water resistance and the presence of free formaldehyde emissions. To meet environmental protection standards, the usage amount needs to be controlled through process optimization. 
Trisodium Polyacrylate Formaldehyde Resin (MF): This resin is formed by the reaction of formaldehyde and melamine. It has high surface hardness, is resistant to water and stains, can withstand high temperatures, and is not prone to cracking. It is the core raw material for manufacturing melamine tableware and is also used in the production of electrical insulation components, decorative panels, flame-retardant coatings and other high-end plastic products. It is widely used in the automotive and electronics industries. 
3. Indirect raw materials for polyoxymethylene (POM) 
Polyoxymethylene, also known as condensation resin, is an excellent engineering plastic and is hailed as "steel-like material". It is produced using formaldehyde as the core raw material. In industry, formaldehyde is first condensed under the action of a catalyst to form a trioxymethylene intermediate, which is then subjected to ring-opening polymerization to generate linear polyoxymethylene resin. The final plastic thus produced has high hardness, high wear resistance, excellent electrical insulation properties, and excellent chemical corrosion resistance. 
Polyoxymethylene plastic is widely used in the manufacturing of automotive parts, gears, bearings, electronic components, textile machinery components, etc., which require high mechanical performance. It is a key plastic material in the field of industrial equipment manufacturing. 
II. Optimize plastic properties to enhance processing and usage value 
Apart from synthetic resins, formaldehyde derivatives can also be used as processing aids for plastics, improving the processing performance, stability and service life of plastics: 
In the production of common plastics such as polyvinyl chloride (PVC), formaldehyde-based additives can act as stabilizers, preventing the decomposition of the plastic during processing and storage due to high temperatures and oxidation, thus maintaining the structural integrity of the material. At the same time, a small amount of formaldehyde participates in the acetalization reaction of polyvinyl alcohol, which can enhance the bonding strength between the plastic and other materials, expanding the composite application scenarios of the plastic. Moreover, polyformaldehyde (the polymer of formaldehyde) can replace formaldehyde aqueous solution for resin synthesis, which can reduce the water content in the reaction system, improve the purity of the resin, and thereby optimize the mechanical strength and high-temperature resistance of the final plastic product. 
III. Controlling the reaction process and regulating the plastic molding characteristics 
The amount of formaldehyde used and the reaction conditions (temperature, pH value) directly affect the degree of polymerization and structure of the resin, thereby regulating the molding properties of the plastic. For example, in the synthesis of phenolic resin, when the molar ratio of formaldehyde to phenol is less than 1, a moldable Novolak resin can be produced, which requires subsequent addition of formaldehyde and heating to complete the curing process; while the thermosetting network polymer directly formed through the reaction can be directly used for molding. By precisely controlling the reaction process involving formaldehyde, various intermediates from liquid prepolymers to solid resins can be prepared, which are suitable for different plastic molding processes such as injection molding, compression molding, and casting. 
IV. Important Notes: Environmental Protection and Safety Management 
Formaldehyde is volatile and irritating. Excessive free formaldehyde can have adverse effects on human health and the environment. Especially in products such as urea-formaldehyde resins, the release amount must be strictly controlled. In industrial production, the Workplace Exposure Limit (WEL) standard should be followed to keep the formaldehyde exposure concentration within a safe range. At the same time, through the development of low-free-formaldehyde resins and the addition of capturing agents, the plastic products can be promoted to develop in an environmentally friendly direction. 
In conclusion, industrial formaldehyde holds a central position as a raw material in plastic manufacturing. By synthesizing different types of resins, optimizing material properties, and regulating molding processes, it supports the production of various plastic products ranging from daily items to industrial equipment, and is an indispensable key link in the plastic industry's value chain.