What is the difference between PEEK and PPS ?

What is the difference between PEEK and PPS ?

PPS (Polyphenylene Sulfide) is a well-known special engineering plastic with extremely low water absorption, chemical corrosion resistance, good wear resistance, excellent dimensional stability, flame retardancy, good electrical insulation, and high temperature resistance. High humidity can still maintain good electrical properties. Good fluidity, easy to form, almost no shrinkage pits when forming. And it has good affinity with various inorganic fillers. It is widely used due to its good performance, especially suitable for corrosive and insulating environments.

PEEK (polyether ether ketone) is a special engineering plastic with excellent comprehensive properties, heat resistance, chemical corrosion resistance, radiation resistance, high tensile strength, electrical properties, flame retardant properties, etc. PEEK materials can be used to process PEEK parts of various specifications, and manufacture high-demand mechanical parts such as gears, bearings, valve seats, sealing rings, pump wear-resistant rings, and gaskets.

So what is the main difference between PPS and PEEK materials?

1. In terms of temperature resistance, PEEK has a long-term temperature resistance of 250°C, an instantaneous use temperature of 300°C, and almost no decomposition at 400°C in a short period of time; PPS can be used at 220°C for a long time, and can reach 260°C in a short period of time. Melting point: PPS is at 280°C, PEEK is at 340°C, and PEEK can maintain high mechanical properties and mechanical strength even at high temperatures.

2. In terms of toughness, whether it is pure resin or glass fiber modification, the elongation at break of PPS is smaller than that of PEEK; in terms of tensile strength, PPS is 105mpa, while PEEK is 115mpa. In general, PEEK is superior to PPS fiber reinforced products in terms of tensile strength, flexural strength, flexural modulus and heat distortion temperature. PPS is difficult to replace when only peek is available, especially at high temperatures.

3. In terms of cost, although PPS is difficult to replace PEEK in terms of performance, the price difference between the two is several times, and the use of PPS can greatly reduce the cost. If the performance of PEEK is excessive in some working conditions or in some frictional occasions or the temperature is low, PPS can be used instead.

In many respects, it is difficult to compare PPS with PEEK, because PEEK is after all the top class of high performance plastics. A few material properties behave comparably, such as flame resistance, electrical insulation properties and dielectric properties.
Especially with regard to the thermal and mechanical properties, the comparison between PPS vs PEEK clearly favours PEEK. Although PPS offers a higher compressive strength compared to PEEK (at 5 % PEEK = 102 MPa vs. PPS =134 MPa). PEEK has a higher ductility (elongation at break PEEK = 15 % vs. PPS = 6.5 %). This results in a higher tensile strength (PEEK = 166 Mpa vs. PPS = 103 MPa) and a higher impact strength (notched Charpy PEEK = 4 kJ/m2 vs. PPS =2,6 kJ/m2) compared to unfilled PPS.

In addition, the lower ductility of PPS compared to PEEK affects the machining behaviour, which is characterised by less burr formation and shorter chips, but a higher risk of cracking.

For some applications, requiring machining operations to realise very delicate structures or micro-holes, PPS can lead to better results than PEEK.

In general, both PEEK and PPS have very good dimensional stability in terms of water absorption and thermal expansion. PPS shows slightly lower water absorption, while PEEK shows slightly lower levels of thermal expansion. While the CLTE of PPS is relatively low up to 100 °C (with 6*10-5/K), the CLTE increases steeply (up to 11*10-5/K at 100~150 °C) in environments above the glass transition temperature.

In addition to the advantages of PEEK having higher ductility, strength and temperature resistance compared to PPS, another advantage of PEEK is its better wear resistance. The data below shows a comparative wear test of different CMP retaining rings.

The advantages of PEEK over PPS are reflected in the comparative costs – PEEK being the more expensive choice. Therefore, PPS plastic is a good alternative especially when the material properties clearly exceed the requirements. In most cases, the lower-cost PPS alternative is then the better choice.

In addition to the over-engineering aspect, PPS material does have one decisive advantage: it has a broader range of chemical resistance than PEEK - only PTFE can top it in this respect.