Polyformaldehyde (English: polyformaldehyde) thermoplastic crystalline polymer. Known as “super steel” or “saigang”, also known as polyoxymethylene. The English abbreviation is POM. Generally, polymers obtained by the polymerization of formaldehyde have a low degree of polymerization and are susceptible to thermal depolymerization. White flammable crystalline powder with formaldehyde odor. It slowly dissolves in cold water and dissolves quickly in hot water. Insoluble in ethanol and ether. Soluble in caustic soda and potassium solutions.
Advantage 1. High mechanical strength and rigidity; 2. Highest fatigue strength; 3. Good environmental resistance and resistance to organic solvents; 4, strong resistance to repeated impact; 5, a wide range of use temperature (-40 ℃ ~ 120 ℃); 6, good electrical properties; 7. Good resilience; 8. Self-lubricating and abrasion resistance; 9. Excellent dimensional stability. Disadvantage Strong acid corrosion, poor weather resistance, poor adhesion, thermal decomposition and softening temperature are close, the oxygen limit index is small.
General performance POM is a hard, dense material with a smooth and shiny surface, which is pale yellow or white, and the thin-walled part is translucent. The burning characteristics are easy to burn, and continue to burn after leaving the fire. The upper end of the flame is yellow and the lower end is blue. Melting dripping occurs, and there is a strong irritating formaldehyde smell and fishy odor. POM is a white powder, which is generally opaque and has good colorability. The specific gravity is 1.41-1.43 g / cm3, the molding shrinkage is 1.2-3.0%, the molding temperature is 170-200 ° C, and the drying conditions are 80-90 ° C for 2 hours. The long-term heat resistance of POM is not high, but it can reach 160 ° C in the short term. The short-term heat resistance of homopolymer POM is more than 10 ° C higher than the copolymerized POM, but the long-term heat-resistant copolymer POM is about 10 ° C higher than the homopolymer POM. It can be used for a long time in the temperature range of -40 ℃ ～ 100 ℃. POM is extremely easy to decompose. The decomposition temperature is 280 ° C. Irritating and corrosive gases occur during decomposition. Therefore, the mold steel should be made of corrosion-resistant materials.
Mechanical properties POM has high strength and stiffness, good elasticity, and good wear resistance. Its mechanical properties are excellent, the specific strength can reach 50.5MPa, and the specific stiffness can reach 2650MPa, which is very close to that of metal. The mechanical properties of POM change little with temperature, and the change of copolymerized POM is slightly larger than that of homopolymer POM. The impact strength of POM is high, but the conventional impact is not as good as ABS and PC; POM is sensitive to notches, and the notch can reduce the impact strength by as much as 90%. The fatigue strength of POM is very prominent. After 10 alternating loads, the fatigue strength can reach 35MPa, while PA and PC are only 28MPa. The creep of POM is similar to that of PA, which is only 2.3% at 20 ℃, 21MPa, and 3000h, and it is little affected by temperature. POM has a small friction factor and good abrasion resistance (POM> PA66> PA6> ABS> HPVC> PS> PC). It has a large limit PV value and good self-lubricity. POM products are prone to scream-like noise when subjected to high loads during grinding.
Electrical performance POM has good electrical insulation and is hardly affected by temperature and humidity; the dielectric constant and dielectric loss change little over a wide range of temperature, humidity and frequency; the arc resistance is excellent, and it can be used at high temperature maintain. The dielectric strength of POM is related to the thickness, which is 82.7kV / mm at a thickness of 0.127mm and 23.6kV / mm at a thickness of 1.88mm.
Environmental performance POM is not resistant to strong acids and oxidants, and has a certain stability to enoic and weak acids. POM has good solvent resistance, can withstand hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricating oils and weak bases, and can maintain considerable chemical stability at high temperatures. Low water absorption and good dimensional stability. The weather resistance of POM is not good. Under the action of ultraviolet rays for a long time, the mechanical properties are reduced, and the surface is powdered and cracked.
Formability Crystal material, narrow melting range, fast melting and solidification, crystallization occurs when the material temperature is slightly lower than the melting temperature, medium fluidity, low moisture absorption, and can be without drying
Paraformaldehyde is a solid formaldehyde with a high formaldehyde content. It is in the form of solid particles and is easy to store and transport. It can be transformed into formaldehyde vapor at higher temperature, which can easily replace high concentration formaldehyde to participate in various reactions. It is beneficial to chemical synthesis such as chemical industry, pharmaceutical and other industrial fields, especially in the synthesis that requires the use of anhydrous formaldehyde as raw material. ,Wide range of uses.
The main aspects are as follows:
(1) pesticides: synthetic acetochlor, butachlor, and glyphosate;
(2) coatings: synthetic high-end automotive paints;
(3) resins: synthetic urea-formaldehyde resin, phenolic resin, polyacetal Resins, melamine resins, ion exchange resins, and various adhesives;
(4) papermaking: synthetic paper reinforcements;
(5) foundry: sand-removing film release agents, synthetic casting adhesives;
(6) aquaculture: fumigation Steam disinfectant.
(7) Organic raw materials: used in the preparation of pentaerythritol, trimethylolpropane, glycerol, acrylic acid, methyl acrylate, methacrylic acid, N-hydroxymethacrylamide, alkylphenol, methyl vinyl ketone and the like.
(8) Others: medicine and disinfection.