Take you to understand the unique properties of special engineering plastics PPS and peek
TIME：2021-10-7
PPS
PPS is a high rigid white powder polymer of crystalline type (crystallinity 55% - 65%), with high heat resistance (the long-term service temperature is 200 ℃ - 220 ℃, and can withstand the high temperature of 260 ℃ in the short term). It is a resin with excellent mechanical strength, rigidity, flame resistance, chemical resistance, electrical characteristics and dimensional stability. It has excellent wear resistance, creep resistance, flame retardancy and self extinguishing. It still maintains good electrical properties under high temperature and high humidity. Good fluidity, easy to form, and there are almost no shrinkage pits during forming. It has good affinity with various inorganic fillers. Its development shortens the difference between standard thermoplastic materials (such as PA, POM, pet...) and advanced engineering plastics.
PPS has the following obvious performance advantages:
(1) Intrinsic flame retardant
Different from PC and PA, PPS pure resin and its glass fiber / mineral powder filled composites can easily reach V without adding any flame retardant- 0@0.8mm V-0 flame retardant grade with even thinner thickness. Although PC and PA have cheaper price and better mechanical strength (especially impact strength) than PPS, halogen-free flame retardant formula (V) is added- 0@0.8mm However, the cost of PC and PA composites will rise sharply, often even higher than PPS materials with the same mechanical strength.
(2) Ultra high fluidity
In the application field of notebook cover plate, this advantage is more obvious than PC. The requirements for bending modulus of the new generation ultra-thin notebook front cover plate (thickness 0.8-1mm) are often as high as 15000 – 17000 MPa (ASTM standard). However, under the pressure of strict cost control in 3C industry, formula designers are often required to choose cheaper glass fiber rather than carbon fiber as reinforcement filler. For PC and its alloys, the poor fluidity determines that the upper limit of glass fiber addition should not exceed 40% (bending modulus can only reach 10000 MPa, ASTM standard). Higher addition will not only seriously affect the fluidity of materials and cause processing difficulties, but also produce problems such as surface floating fiber, serious warpage and poor mechanical properties. For the semi crystalline PPS, its very high fluidity can easily allow the filling amount of glass fiber to exceed 50%. Meanwhile, in the process of high-temperature melt blending and extrusion, the lower viscosity of PPS compared with PC can make the glass fiber undergo a lower degree of shear and extrusion, so as to have a longer retention length in the final injection molded products and further improve the modulus.
(3) Ultra low water absorption
This advantage is mainly for PA. In terms of fluidity, high filled PA and PPS are equal; For mechanical properties, PA composites with the same filling amount are more dominant. However, in addition to the limitation of halogen-free flame retardant, another factor restricting the application of PA is its high water absorption: compared with the 0.6% - 1% water absorption of high-temperature nylon PA6T, the 0.03% water absorption of PPS is almost negligible. As a result, the defective rate of PPS products due to water absorption deformation is much lower than that of PA products under the same conditions.
(4) Unique metal texture and higher surface hardness
When PPS injection molded parts fall off the desktop, they will make a very crisp collision sound unique to PPS. Through the matching of special mold and reasonable mold temperature, PPS injection molded parts will also make a sound similar to metal collision under the touch of hands, and their surface will be as smooth as a mirror and have a metallic luster.
PEEK
Peek is a special engineering plastic with excellent comprehensive properties. It has excellent heat resistance, chemical corrosion resistance, radiation resistance, electrical properties, flame retardancy and so on. Its molecular chain is a polymer composed of benzene ring and connected ketone group and ether group. Benzene environmental protection proves that PEEK material has good rigidity, and ether bond ensures peek has good toughness. Therefore, peek is a comprehensive material with both toughness and rigidity.
Peek has the following outstanding performance:
(1) Extremely high heat resistance. It can be used for a long time at 250 ° C, and the instantaneous service temperature can reach 300 ° C. it hardly decomposes in a short time at 400 ° C.
(2) Excellent mechanical properties and dimensional stability. Peek can maintain high strength at high temperature. The bending strength at 200 ° C can still reach 24 MPa, and the bending strength and compression strength at 250 ° C can reach 12 ~ 13 MPa. It is especially suitable for manufacturing components that can work continuously at high temperature. Peek has high rigidity, good dimensional stability and small linear expansion coefficient, which is very close to metal aluminum. In addition, peek also has good creep resistance and can bear great stress during the service life without obvious extension due to the extension of time.
(3) Excellent chemical resistance. Even at high temperature, peek can well resist the corrosion of most chemicals, and its corrosion resistance is similar to that of nickel steel. In general, the only thing that can dissolve peek is concentrated sulfuric acid.
(4) Good hydrolysis resistance. It can resist chemical damage caused by water or high-pressure water vapor. Under high temperature and high pressure, peek components can work continuously in water environment and still maintain good mechanical properties. If it is immersed in 100 ° C water for 200 days, the strength remains almost unchanged.
(5) Good flame retardancy. It can reach UL 94 V-0, has self extinguishing property, and releases less smoke and toxic gases under flame conditions.
(6) Good electrical performance. Peek maintains electrical properties over a wide frequency and temperature range.
(7) Strong radiation resistance. Peek has a very stable chemical structure, and peek components can work normally under high-dose ionizing radiation.
(8) Good toughness. The fatigue resistance to alternating stress is the most outstanding of all plastics, which is comparable to alloy materials.
(9) Excellent friction and wear resistance. It can maintain high wear resistance and low friction coefficient at 250 ° C.
(10) Good processing performance. Easy extrusion and injection molding, and high molding efficiency.
