Polyoxymethylene (POM), whose primary structural unit is -CH₂O-, is the most widely used general-purpose engineering plastic after polyamide (PA) and polycarbonate (PC). It is currently widely used in high-end electronics, automotive parts, mechanical components, gears, and other fields.
It can operate for long periods of time in temperatures ranging from -40°C to 100°C, maintaining excellent creep, fatigue, wear, and chemical resistance even under harsh operating conditions. These properties and cost advantages make it a viable alternative to non-ferrous metals such as brass, aluminum, and zinc in gears, electrical housings, other automotive parts, and high-end electronics. It has been called the "metal in plastic" and is often referred to as "plastic steel" or "super steel."
Performance Characteristics
1. Metal-like
Polyoxymethylene is a highly crystalline polymer with metal-like hardness, strength, and stiffness, making it one of the engineering plastics with mechanical properties closest to those of metal.
2. Self-lubrication and Fatigue Resistance
Polyoxymethylene exhibits excellent self-lubrication and fatigue resistance over a wide temperature and humidity range. It also has advantages such as a low coefficient of friction, resistance to organic solvents, and ease of molding.
3. Thermal Stability
Polyoxymethylene (POM) has low water absorption and is dimensionally stable, allowing for long-term use over a wide temperature range (-40°C to 100°C). It also exhibits high hot strength, flexural strength, and fatigue resistance. The heat deflection temperature of homopolyoxymethylene is 136°C, while that of copolymers is 110°C. Polyoxymethylene can be used for long periods in high-temperature environments with minimal change in mechanical properties.
4. Wear Resistance
Polyoxymethylene exhibits excellent wear resistance due to its high bond energy and high cohesive energy. The amorphous portion aggregates on the surface of the spherulites, acting as a lubricant and reducing friction and wear.
Modification Options
1. Polyoxymethylene Reinforcement
Filling and glass fiber (GF) reinforcement are common modification methods. Filler modification can be categorized as either inorganic or organic.
Filler modification can reduce raw material costs, but it sacrifices certain properties to achieve the desired performance improvement. Glass fiber reinforcement allows the fibers to withstand certain stresses, thereby improving the mechanical strength and dimensional stability of the composite material. However, this can reduce wear resistance.
2. Wear Resistance Modification of Polyoxymethylene
Wear resistance modification of polyoxymethylene (POM) can be achieved through chemical and physical modification. Chemical modification involves adding new monomers during the polymerization stage to graft lubricating molecular segments onto the molecular chain, thereby improving the wear resistance of POM. Physical blending is a common modification method that is simple to operate and offers significant results.
Physical blending typically enhances the wear resistance of polyoxymethylene (POM) by adding additives. Common additives include functional polymers, common metal powders, silicone oil, mineral oil, grease, and other lubricants.
3. Toughening Modification of Polyoxymethylene
Because POM lacks toughness and is prone to fracture during part processing, it requires toughening modification. Common methods include elastomer toughening, rigid particle modification, and alloying. Elastomer toughening improves the impact toughness of polyoxymethylene by introducing elastomer particles. This method is simple to operate and offers significant results. Rigid particle toughening not only enhances the material's impact resistance, but also improves its strength, rigidity, and heat resistance.
Alloying modification involves blending polyoxymethylene with other resins and additives to form alloys, enhancing its toughness and wear resistance while maintaining the excellent properties of polyoxymethylene.
Main Applications
1. Automotive Industry
Manufacturing automotive pumps, carburetor components, fuel lines, power valves, universal joint bearings, motor gears, crankshafts, handles, instrument panels, window lifts, electric switches, seat belt buckles, etc.
2. Mechanical Manufacturing
Widely used in transmission components such as gears, drive shafts, chains, valves, valve stem nuts, bearings, cams, impellers, rollers, nozzles, guides, bushings, pipe fittings, and other mechanical structural components.
3. Electrical and Electronics Industry
It exhibits excellent electrical insulation, heat resistance, and chemical resistance, making it commonly used in the manufacture of electrical insulators, sockets, switches, connectors, and other electronic components.
4. Home Appliances
Due to its excellent strength, rigidity, and wear resistance, polyoxymethylene is widely used in the manufacture of home appliances and household items. For example, it can be used to make appliance housings, furniture pieces, home decoration materials, sinks, water heater components, etc.
5. Precision Instruments
It is used to manufacture shelf supports, covers, friction pads, and parts for clocks, cameras, and other precision instruments.
In addition to the above applications, POM-modified plastics can also be used in corrosion-resistant fire hydrants, pen barrels and pen caps, toys, digital products, zippers, mascara wands, and other consumer products.
