Research Progress on Modified Polyether Ether Ketone (PEEK) Composites

Polyether ether ketone (PEEK) is a representative material in the polyaryletherketone family. With its semi-crystalline nature, aromatic structure, and excellent comprehensive properties, it stands out among engineering plastics. The benzene rings in its molecular chain endow it with outstanding heat resistance, wear resistance, and chemical corrosion resistance, while the ether linkages and carbonyl groups provide good flexibility and processability. These characteristics make PEEK highly favored in fields such as petrochemicals, mechanical manufacturing, aerospace, and medical implants. However, pure PEEK resin suffers from significant brittleness, weak shear resistance, a relatively low upper limit of service temperature, and high cost, which limit its application in extreme conditions and high-performance demanding fields.

To overcome these limitations, researchers have optimized the performance of PEEK through various modification methods. The modification methods are mainly divided into two categories: polymer blending modification and inorganic filler modification. Polymer blending modification involves blending with other high-performance polymers such as polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and polyetherimide (PEI), utilizing the synergistic effect to improve the mechanical properties, thermal stability, and tribological properties of PEEK.

Inorganic filler modification enhances the mechanical properties, thermal conductivity, bioactivity, and other characteristics of PEEK by introducing fibers (carbon fibers, glass fibers, aramid fibers) or nanoparticles [ZnO, SiO₂, hydroxyapatite (HA)]. The incorporation of carbon fibers and glass fibers significantly improves the rigidity and heat resistance of PEEK, while nanoparticles optimize the crystallization behavior and functional properties of PEEK through their high specific surface area and interfacial effects. In addition, the introduction of novel nanofillers such as graphene, carbon nanotubes, and SiC further expands the application potential of PEEK in electronic devices, thermal management, and high-end medical fields.

Despite significant progress in modification research, challenges remain in filler dispersion, process stability, and cost control. This paper systematically reviews the latest research progress in modified PEEK composites, analyzes the mechanisms and effects of various modification methods, and discusses future development directions, aiming to provide a theoretical basis and technical reference for the design and application of high-performance PEEK composites.

PEEK, as the core member of the polyaryletherketone family, is a semi-crystalline thermoplastic aromatic polymer composed of linear molecular chains. Its molecular backbone is rich in benzene rings, endowing it with excellent comprehensive properties, including outstanding heat resistance, wear resistance, fatigue resistance, radiation resistance, peel resistance, and creep resistance. Meanwhile, the ether bonds and carbonyl groups in the molecular chain provide the necessary flexibility and good processability, making it highly favored as a specialty material in fields such as petroleum, chemical engineering, and machinery. However, PEEK also has limitations: the pure resin is quite brittle, has weak shear resistance, a relatively low upper usage temperature, and is expensive, which restricts its application in areas requiring extremely high wear resistance, impact resistance, and corrosion resistance. Therefore, researchers at home and abroad are committed to modifying PEEK, aiming to reduce costs while improving its compatibility, insulation, impact strength, and compressive strength.

Resin-filled modification involves compounding fillers with resin to improve the resin’s properties, such as rigidity, heat resistance, and processability, thereby enhancing the dimensional stability of products and components. Common filling and reinforcing materials include fibers, nanoparticles, graphene, and others.

The most common method for modifying PEEK at present is fiber reinforcement. Numerous studies have found that PEEK materials reinforced with glass fiber (GF), carbon fiber (CF), and aramid fiber (AF) exhibit higher heat distortion temperatures and lower shrinkage, offering broad application prospects in high-tech fields such as aerospace. Carbon fiber has high specific strength and specific modulus, and also possesses excellent chemical properties such as corrosion resistance, oxidation resistance, water resistance, and oil resistance.

Glass fiber (GF) has advantages such as high strength, high modulus, good heat resistance, and low cost, making it an ideal polymer reinforcement filler. As a modifying filler for PEEK, glass fiber can significantly enhance the mechanical properties of composites, such as tensile strength and rigidity; it also improves dimensional stability and heat resistance while reducing the coefficient of thermal expansion. In addition, the inclusion of glass fiber can optimize the processing flow of PEEK and impart better wear resistance to the material, further expanding its application potential in fields such as automotive, electronics, and aerospace while maintaining the original excellent properties of PEEK.

The addition of aramid fibers can significantly enhance the constraint effect of the composite material by inducing interfacial crystallization, thereby increasing the restriction on the molecular mobility of the PEEK matrix, which in turn improves the material's heat resistance and mechanical properties. Meanwhile, the insulating properties of aramid make it suitable for dielectric performance studies.

Inorganic nanoparticles (such as nano ZnO, SiO2, BN, hydroxyapatite, etc.) can effectively enhance the comprehensive performance of PEEK. Their high specific surface area and interfacial effects can improve mechanical properties while maintaining lightweight characteristics, as well as improve processing fluidity and moldability. Nanoparticles can also enhance wear resistance, dimensional stability, and fatigue resistance, while some particles can impart bioactivity to PEEK, expanding its medical applications. This modification achieves a synergistic enhancement of multiple properties while retaining the original advantages of PEEK.

Zinc oxide (ZnO)–modified PEEK can significantly enhance the electrical properties of the material, such as breakdown field strength and nonlinear coefficient, while avoiding damage to the polymer structure caused by high-temperature sintering, thereby providing a new approach for developing high-performance functional composite materials.

The addition of SiO₂ can regulate the crystallization behavior of PEEK by reducing the mobility of molecular chain segments to lower crystallinity while refining the spherulite size, thereby optimizing the material’s mechanical properties and thermal stability. It is suitable for high-performance engineering applications sensitive to crystallization characteristics.

The oriented arrangement of BN nanosheets (BNNSs) significantly enhances the thermal conductivity of PEEK while maintaining excellent electrical insulation and mechanical strength, making it suitable for thermal management in high-power electronic devices.

The advantages of hydroxyapatite (HA)-modified PEEK lie in its significantly enhanced bioactivity and hydrophilicity, enabling better integration with bone tissue and promoting osteoblast adhesion and growth, while maintaining the excellent mechanical properties and chemical stability of PEEK. This modification effectively addresses the insufficient osseointegration caused by the bioinertness of PEEK, providing improved surface performance for orthopedic implants.

New nano-enhancement technologies, particularly novel nano-fillers represented by graphene (GO), carbon nanotubes (CNTs), and silicon carbide (SiC), have opened up broad prospects for the modification of PEEK. By selecting the type of filler, modifying it, and optimizing the dispersion process, PEEK composites can achieve significant or even breakthrough improvements in various aspects such as mechanical strength/modulus, hardness/wear resistance, toughness, high-temperature performance, thermal/electrical conductivity, tribological performance, dimensional stability, and functionality. This greatly expands the application potential of PEEK in high-end fields such as extreme conditions, precision components, electronics, aerospace, and high-end medical implants. However, the cost of novel nano-fillers, the difficulty of dispersion, and the stability of large-scale production processes remain issues that require ongoing research and resolution.

Graphene-modified PEEK composites combine the high thermal conductivity of graphene with the lightweight and easy-to-process characteristics of PEEK, significantly enhancing the material’s thermal conductivity while also improving its mechanical strength, making them suitable for the heat dissipation requirements of highly integrated electronic devices.

The incorporation of CNTs can significantly enhance the interfacial bonding strength and mechanical properties of the material, which is attributed to their high specific surface area and excellent mechanical properties that effectively improve the interfacial bonding between PEEK and other substances, while the synergistic effects of chemical grafting and physical anchoring can further enhance stress transfer efficiency.

The high hardness and wear resistance of nano-SiC can effectively reduce the friction coefficient of PEEK and improve its wear resistance, while maintaining PEEK’s high-temperature resistance and mechanical strength.

After modification through blending, inorganic fillers, and novel nanomaterials, the overall performance of PEEK has been significantly enhanced, expanding its application potential in high-end fields such as aerospace, medical implants, and electronic devices. In blend modification, PEEK is combined with other high-performance polymers to optimize its mechanical, thermal stability, and tribological properties. Modification with inorganic fillers introduces fibers and nanoparticles, which not only enhance the mechanical strength of PEEK but also impart bioactivity and functionality. The incorporation of novel nanomaterials has pushed the performance limits of PEEK in terms of mechanics, thermal and electrical conductivity, and wear resistance. However, filler dispersion, process stability, and the cost of large-scale production remain challenges. In the future, by optimizing modification processes, developing new fillers, and integrating digital manufacturing technologies, PEEK composites are expected to achieve large-scale application in more extreme operating conditions and fields with high-performance demands, becoming a core material among next-generation high-performance engineering materials.