Polyformaldehyde (English: polyformaldehyde) is also known as acetaln resins; polyoxymethylenes. Full name polyacetal resin, referred to as polyformaldehyde, thermoplastic crystalline polymer. Known as "super steel" or "sai steel". The structural formula is as follows, the English abbreviation is POM. The polymer obtained through formaldehyde polymerization has a low degree of polymerization and is susceptible to thermal depolymerization.
Around 1955, DuPont of the United States obtained formaldehyde homopolymer from formaldehyde polymerization. POM is easy to crystallize, and the crystallinity is above 70%. The melting temperature of homopolyformaldehyde is about 180 ° C. It is another engineering plastic with excellent comprehensive properties after polyamide. It has high mechanical properties such as strength, modulus, abrasion resistance, toughness, fatigue resistance and creep resistance. It also has excellent electrical insulation properties. , Solvent resistance and processability, is one of the five general engineering plastics.
Physical and chemical properties of POM polyformaldehyde:
POM is a linear polymer with no side chains, high density and high crystallinity, and has excellent comprehensive properties. POM has good oil resistance, good solvent resistance, resistance to hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricants, etc., and can maintain considerable chemical stability at high temperatures. It is not resistant to oxidants and acids but has a certain stability to enoic and weak acids. It is not resistant to strong alkalis and sunlight.
POM is a smooth, shiny, hard and dense material with a pale yellow or white color. It can be used for a long time in the temperature range of -40-100 ° C. Its abrasion resistance and self-lubrication are also superior to most engineering plastics. Tensile strength of 70MPa, low water absorption, and good dimensional stability. These properties are better than nylon. Polyoxymethylene is a highly crystalline resin. It is the toughest of thermoplastic resins and has good creep resistance even at low temperatures. Variable properties, geometric stability and impact resistance. High heat resistance, bending strength, fatigue resistance, high abrasion resistance and electrical properties. Specific gravity 1.43, melting point 175 ° C, tensile strength (yield) 70MPa, elongation (yield) 15%, (fracture) 15%, impact strength (no gap) 108KJ / m2, (with gap) 7.6 KJ / m2.
POM has both homopolymer and copolymer materials. Homopolymer materials have good ductility and fatigue resistance, but they are not easy to process. Copolymer materials have good thermal and chemical stability and are easy to process. Both homopolymer and copolymer materials are crystalline materials and do not easily absorb moisture. The high degree of crystallization of POM results in a relatively high shrinkage rate, which can be as high as 2% to 3.5%. There are different shrinkage rates for various reinforced materials.
density
g / cm3
1.39-1.43
Water absorption
%
0.2
Continuous use temperature
℃
—50--105
Yield strength
MPa
63
Yield strain
%
10
Ultimate tensile strength
MPa
Ultimate tensile strain
%
31
Impact toughness
Kj / ㎡
Notch impact toughness
Kj / ㎡
6
Rockwell hardness
MPa
135
Shore hardness
MPa
85
Flexural strength
MPa
Elastic Modulus
MPa
2600
Softening temperature
℃
150
Heat distortion temperature HDT
℃
155
Coefficient of thermal linear expansion
1.1
Thermal conductivity
W / (m × K)
031
Coefficient of friction
0.35
Application of POM polyformaldehyde:
Polyoxymethylene (POM) is a kind of engineering plastic with excellent performance. It is known as "steel grabbing" and "super steel" in foreign countries. It is mainly used for injection molding, and secondly used for extruding plates and bars. POM has similar metal hardness, strength and rigidity. It has good self-lubricity, good fatigue resistance, and elasticity in a wide range of temperature and humidity. In addition, it has good chemical resistance. Character. At a lower cost than many other engineering plastics, POM is replacing some markets traditionally occupied by metals, such as replacing zinc, brass, aluminum, and steel to make many parts. Since its inception, POM has been widely used in electronics, electrical, and machinery. , Instrument, daily light industry, automobile, building materials, agriculture and other fields, used to manufacture various sliding and rotating mechanical parts, making various gears, levers, pulleys, sprockets, especially suitable for bearings, hot water valves, precision measurement Valves, chain links and rollers of conveyors, flow meters, automobile interior and exterior handles, cranks and other window turning machinery, oil pump bearing seats and impeller gas switching valves, electronic switch parts, fasteners, terminal mirror covers, electric fan parts, Heating plates, instrument buttons; bearings for audio and video tapes; various plumbing and agricultural sprinkler irrigation systems, as well as parts for valves, sprinklers, faucets, and bathtubs; switch keyboards, buttons, audio and video tape reels; temperature-controlled timers; power tools, garden tools ; In addition, it can be used as surfboard, sailboat and various sled parts, watch micro gears, frame accessories for sports equipment and Coated with a variety of buckles, fasteners, lighter, zippers, buckles; Medical Devices cardiac pacemakers; artificial heart valve, the apical vertebra, prostheses and the like. In many new fields of application, such as medical technology, sports equipment, etc., POM has also shown a good growth trend.