Polyphenylene ether plastics

Polyphenylene ether is also known as poly2,6-dimethyl1,4-benzene support ether resin, abbreviated as PPO in English. Pure PPO is difficult to process and difficult to be applied in practice, and it was not until the development of modified MPPO that it has developed rapidly and has become the fifth largest general engineering plastic after PA, PC, POM, PBT and PET.
The purpose of PPO modification is to improve the processing performance, and at present, it is mainly the blending or grafting of PPO and PS, that is, PPO/PS modified varieties.
The outstanding properties of PPO are high rigidity, good creep resistance, high tensile strength, the best electrical properties among engineering plastics, and small linear expansion coefficient, etc., and the disadvantages are poor fatigue resistance and stress crack resistance.
MPPO is widely used in the automotive, electronic and electrical, office supplies and machinery industries.
1. Performance of PPO
(1) General performance The appearance of PPO and MPPO is transparent amber, non-combustible, extinguished when leaving the fire, the flame is bright with thick black smoke, and emits a flower and fruit odor. Low water absorption, resistant to water and water vapor. Small shrinkage and high dimensional stability.
(2) Mechanical properties PPO has outstanding mechanical properties, especially tensile strength, impact strength and creep resistance. Taking creep resistance as an example, the creep value is only 0.75% under a load of 2MPa for 3000h, while under the same conditions, PC is 1%, POM is 2.3%, PA6 is 2%, and ABS is 3%.
The impact strength of PPO is higher than that of PC. The mechanical strength of PPO changes little with temperature and humidity, and the tensile strength does not decrease significantly after 700h in boiling water.
PPO has relatively high rigidity and hardness, good wear resistance and low coefficient of friction. However, PPO has poor fatigue resistance and stress crack resistance.
(3) Thermal performance PPO has high heat resistance, and the heat deflection temperature of pure PPO can reach 173 °C
It can be used for a long time in the range of -127~121°C, and the intermittent use temperature can reach 205°C under no-load conditions. The heat-resistant temperature of MPPO is slightly lower, but higher than that of PC, PA and ABS, and close to PF (phenolic resin). The coefficient of thermal expansion of PPO is the lowest among plastics, close to that of metal, and suitable for the placement of metal inserts
(4) Electrical properties PPO has excellent electrical properties, its dielectric constant and dielectric loss tangent value are relatively low, which is the lowest among engineering plastics in the power frequency range, and changes very little in a wide range of frequency, temperature and humidity. It has high dielectric strength but poor corona resistance.
(5) Environmental performance PPO is stable to dilute acids, alkalis and salts, swells in aliphatic hydrocarbons and aromatic hydrocarbons such as ethyl acetate, acetone and gasoline, and dissolves in chlorinated hydrocarbons; The antioxidant activity of PPO is not good, so phosphate ester antioxidants need to be added.
2. Molding and processing of PPO
(1) Processing characteristics
Although the water absorption of PPO is small, it needs to be dried before processing, and the drying conditions are: 130 °C, 2~4h, and the thickness of the material layer is less than 50mm.
The melt of PPO is a Newtonian fluid at low temperature and a non-Newtonian fluid at high temperature.
The PPO molecular chain is rigid, and the product is prone to internal stress, so it is best to heat treat it in glycerol at 180 °C or add 2% ethyloctyl epoxyoctamate.
PPO scrap can be reprocessed up to three times.
(2) Processing method
MPPO can be processed by injection molding, extrusion, pressing and other thermoplastic processing methods:
The L/D of the injection screw should be greater than 25, and the compression ratio should be greater than 2.5~3.5.
Extrusion: It is best to use an exhaust extruder.
3. Modified varieties of PPO
PPO is blended and copolymerized with PS to improve processability.
PPO is blended with ABS to improve stress crack resistance.
PPO is blended with other engineering plastics to improve overall performance.
Glass fibers are reinforced with PPO to further increase its mechanical properties
4. The application scope of PPO
(1) About 30% of PPO for electronic appliances is used in electronic appliances, which is suitable for wet and load-bearing insulation occasions, and can be used on ultra-high frequency. Such as coil winding tubes, binding posts, junction boxes, electrical switches, battery adapters, timers, relays, UHF tuners, tube sockets and high-voltage insulating covers.
(2) Auto parts In the United States, 40% of PPO is used in the automotive industry to replace cast iron, cast aluminum, ABS and PA in large quantities. Such as instrument panels, bumpers, auto-positioning buttons, antifreeze grilles, shock absorbers, booms, heater brackets and baffles, speaker grilles, etc.
(3) Office equipment 40% of PPO in Western Europe and Japan is used for office equipment, such as computers, typewriters, fax machines, copiers, printing machine housings, etc.
(4) The amount of machine parts accounts for about 10% of PPO, which can be used for silent gears, cams, bearings and fasteners.