PEI Vs.PEEK

PEI and PEEK are both high-performance engineering plastics that are similar in many ways, but also have some key differences.

Polyether ether ketone (PEEK): PEEK is a thermoplastic engineering plastic with excellent properties, which is formed by the polycondensation of 4% amide or carboxamide groups with more than 60% diols.PEEK has good high temperature resistance, chemical stability, oxidation resistance and mechanical strength. It has a melting point of up to 342°C and a thermal decomposition temperature of up to 340°C, which makes it perform well in high-temperature environments. In addition, PEEK has excellent electrical insulation properties and flame retardant properties.

Polyether ether ketone copolymer (PEI): PEI is a copolymer of PEEK and a number of other polymers, usually consisting of 35-45% PEEK and 65-75% other polymers. the properties of PEI are in between those of PEEK and those of traditional engineering plastics, such as Pa66, Pa6, etc. PEI has a very high degree of thermal and chemical stability, mechanical strength, as well as good electrical insulation properties and flame retardancy. PEI has a high thermal stability, chemical stability and mechanical strength, as well as good electrical insulation properties and flame retardant properties.The melting point of PEI is as high as 290℃, and the thermal decomposition temperature is as high as 248℃.

PEEK and PEI are different in the following aspects:

1. Thermal stability: Although the thermal decomposition temperature of PEI and PEEK is very high, but the thermal stability of PEI is better, PEI can still maintain its mechanical properties and chemical stability at higher temperatures, while PEEK can maintain its mechanical properties and chemical stability.

Chemical properties are stable, while PEEK will soften, flow and oxidize at higher temperatures.

2. Mechanical Properties: PEI is slightly better than PEEK in some mechanical properties, for example, PEI's tensile strength and stiffness are slightly higher than PEEK's. However, this difference is not significant in most applications, and because of PEEK's high melting point and good fluidity, it may be more advantageous in the injection molding process.

3. Cost: The cost of PEI is usually higher than that of PEEK due to the relative complexity of the production process and the higher cost of raw materials. however, this difference may be offset in mass production.

4. High Temperature Performance: One of the main differences between PEEK and PEI is their different morphological structures. PEI is amorphous, while PEEK is semi-crystalline (and contains both amorphous and crystalline regions). This may sound like a useless fact, but it has a significant impact on performance at elevated temperatures, especially above the glass transition temperature of each material.

PEEK has a glass transition temperature (Tg) of about 289F, while PEI has a Tg of about 420F, but PEEK is used consistently in applications at temperatures of 480F (and for short periods of time at even higher temperatures), while Ultem's maximum continuous operating temperature is typically reported as 340 degrees Fahrenheit. This is because at the Tg of the material, the amorphous regions soften or rubberize, while the crystalline regions are unaffected. Therefore, the maximum usable service temperature for amorphous materials is correspondingly limited.

5. Electrical Properties: Because of their electrical properties, both materials are widely used in electronic components, including semiconductor test sockets and electrical connectors. PEI has the highest dielectric strength of any commercially available thermoplastic at 830 V/mil (according to ASTM D149) (or if it can talk). PEEK has a reported dielectric strength of 480 V/mil. PEEK reports a dielectric strength of 480 V/mil. For applications requiring lower levels of resistivity, grades of static dissipative and antistatic materials are available.

6. Corrosion Resistance: Both materials are steam-resistant and are suitable for reusable medical parts with repeated autoclave cycles. PEEK is widely used in downhole oil and gas applications due to its resistance to harsh chemicals including H2S. While PEI is also resistant to a wide range of chemicals, its brittleness makes it more susceptible to environmental stress cracking.PEI has relatively limited compatibility with aromatic and chlorinated hydrocarbons, ketones, esters, and strong bases (e.g., sodium hydroxide).

PEI has been shown to exhibit negligible changes in mechanical properties after prolonged exposure to UV radiation.PEEK is subject to outdoor weathering, but data suggest that the effect on mechanical properties is minimal, at least within one, and can be reduced by the inclusion of colored pigments. The radiation resistance of various high performance engineering plastics has been studied and PEEK (and other polyaryletherketones) have been found to exhibit the highest levels of radiation resistance.

7. Wear Performance, Flammability, Industry Compliance and Relative Costs

For wear applications, PEEK is often preferred because of its higher ultimate PV capability and significantly lower wear rates. Specialty bearing grades of PEEK include filler packs with various filler levels of PTFE, carbon fiber and graphite powder to reduce friction and extend wear life.

8. Flame Retardant: Both materials are flame retardant and maintain a UL 94 V-0 flammability rating in thin cross sections. PEI is rated at 5VA at 1.6mm and has a higher limiting oxygen index (LOI) of 47%. Standard PEEK and PEI grades are FDA compliant. Both are also readily available in USP Class VI-compliant grades for medical applications. These materials can meet many other industry compliance requirements, but a complete list is beyond the scope of this article. It is also worth noting that natural PEI is a translucent amber color, while natural PEEK is an opaque tan color. Both materials are available in natural and black rods and sheets. Natural colored PEEK tubing is also readily available.

Finally, PEEK profiles cost about three times as much as their PEI counterparts. However, for seals or rings (especially larger diameters), this price difference is often mitigated by the wide availability of PEEK tubing. Hopefully you have found the above helpful in differentiating between PEI and PEEK, and while both materials offer high performance at elevated temperatures and even have some applications in common, their properties are often distinct enough to make one candidate more suitable for a particular end use.