Thermoplastic Composite Resins: PEEK, PEKK, PAI, and Beyond

Review of Thermoplastic Composite Resins

In recent years, fiber-reinforced thermoplastic composites based on thermoplastic resins have surged in popularity, with researchers and industries worldwide focusing on developing these high-performance materials. The most common thermoplastic molding processes include compression molding, resin injection molding, filament winding, and pultrusion. Choosing the appropriate type of plastic resin is crucial in these processes, as it directly affects the final product's characteristics and performance. Each resin type offers a range of advantages, allowing manufacturers to tailor their material selection to specific product requirements.

Common Thermoplastic Resins for Composites

The most common high-performance thermoplastic resins—Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), Polyamide-imide (PAI), Polyphenylene sulfide (PPS), Polyetherimide (PEI), Polyethersulfone (PES), and Liquid Crystal Polymer (LCP)—perform well in high-temperature environments. Once hardened, they do not absorb water or degrade in humid conditions. These resins, reinforced with high-performance fibers, extend the shelf life of prepregs without refrigeration and exhibit excellent impact resistance and vibration damping. They also offer opportunities for using recycled content and simplify waste and scrap structure recycling.

Polyetheretherketone (PEEK) Resin

PEEK resin has a high glass transition temperature (143°C) and melting point (334°C), making it reliable for applications requiring heat resistance. It also boasts excellent creep resistance, strong tensile strength, and is environmentally friendly.

Common Applications: PEEK is widely used in aerospace, automotive, biomedical, and electrical fields. It is suitable for manufacturing bearings, insulated cables, safety gears, pumps, heavy machinery parts, valves, compressors, semiconductors, etc. Major PEEK producers in China include Kangsheng New Materials, Water Co., Zhongyan ZYPEEK Co., ARKPEEK, and Zhaomin Technology.

Polyetherketoneketone (PEKK) Resin

PEKK is a high polymer composed of diphenyl ether and isophthaloyl chloride or terephthaloyl chloride, with a repeating unit containing one ether bond and two ketone bonds in its main chain structure.

Properties: PEKK resin offers extremely high temperature resistance, with long-term usage temperatures of 250~260°C and short-term usage up to 300°C. It has high stiffness, tensile strength, compressive strength, impact resistance, excellent flame resistance, inherent flame retardancy, and low smoke emission. It also has superior chemical resistance, dielectric strength, insulation properties, and friction resistance.

Common Applications: PEKK is used in high-temperature structural and electrical insulation materials, non-stick coatings, carbon fiber thermoplastic composites, 3D printing filaments and powders, injection-molded products, extruded boards, electronic films, and more. It is widely applied in aerospace, 3D printing, 5G electronics, oil and gas extraction, medical devices, dental and bone implants, and new energy vehicles. Shandong Kangsheng New Material Co. is currently the only domestic company with independent intellectual property rights and the capability to produce PEKK.

Polyamide-imide (PAI) Resin

PAI resin, a high polymer with alternating imide rings and amide bonds, has unmatched strength among unreinforced industrial plastics, with a tensile strength exceeding 172 MPa and a heat distortion temperature of 274°C under a 1.8 MPa load.

Properties: PAI retains the excellent properties of polyimides, such as heat resistance, mechanical properties, creep resistance, radiation resistance, and chemical stability, while being easier to process. It also has better rigidity and chemical stability compared to polyimides and is more soluble in organic solvents.

Common Applications: PAI bonds well to metals and other materials, making it suitable for use in enameled wire coatings, impregnating varnishes, films, laminates, coatings, and adhesives. For example, enameled wires made from PAI are used in H-class deep-sea diving motors, laminates in printed circuit boards and sockets, and films as insulating wrapping materials.

Polyphenylene Sulfide (PPS) Resin

PPS, the most widely used thermoplastic resin among polyarylene sulfides (PAS), is composed of alternating benzene rings and para-sulfur atoms. The rigid structure of the benzene rings gives it high crystallinity and corrosion resistance, while the flexible sulfide bonds and inherent flame retardancy ensure it meets UL-94-V0 level flame resistance without added flame retardants.

Common Applications: Modified PPS resins can be used in engineering plastics, fibers, films, and coatings across various fields. Major PPS producers in China include Zhejiang NHU, Chongqing Polyseal, Shandong Sainji, Guangdong Hongshu, Zhuhai Changxian, Jiangsu Ouruida, Suzhou Napol, Sichuan Zhongke Xingye, and Chengdu Letian Plastics.

Polyetherimide (PEI) Resin

PEI, known as Polyetherimide, is an amber-colored amorphous thermoplastic engineering plastic with flexible ether bonds (-R-O-R-) introduced into the rigid polyimide long-chain molecules. It combines aromatic amine functional groups with ether bonds, offering a lower-cost, higher-yield thermoplastic alternative to other aromatic polyimides.

Common Applications: PEI is used in electronics, electrical, and aerospace industries as a metal substitute in traditional products and daily life items. Notably, it can replace metals in manufacturing optical fiber connectors, optimizing component structures, simplifying manufacturing and assembly processes, and reducing final product costs by about 40%. PEI composites with carbon fiber are used in various helicopter components, and PEI foam is used as insulation and soundproofing material in transportation machinery and aircraft.

Liquid Crystal Polymer (LCP)

LCP, an all-aromatic polyester, features unique molecular structures with one- or two-dimensional long-range molecular orientation, offering high heat resistance, high modulus, low melt viscosity, minimal thermal expansion, low dielectric loss, and high strength.

Common Applications: LCP is used in engineering plastics, films, and fibers. Applications include high-speed connectors, 5G base station antenna vibrators, and FCCL substrate materials for antennas. Major domestic LCP producers include Kingfa Sci. & Tech., Water New Material, Shanghai Prite, Nantong Haidi, Nanjing Qingyan, Ningbo Haigera, and Ningbo Ju Jia New Material.

Advantages of Thermoplastic Composite Molding

1, Design Flexibility: Thermoplastic materials provide unparalleled design flexibility, allowing manufacturers to create complex shapes, textures, and custom designs using thermoforming technology. This versatility makes them ideal for producing intricate and visually appealing products tailored to specific customer needs.

2, Cost-Effectiveness: Thermoformed plastic resins are economically advantageous, involving minimal mold and setup costs, making them suitable for both small- and large-scale production. Additionally, the lightweight nature of thermoplastic materials helps reduce transportation and handling costs.

3, Recyclability and Sustainability: Many thermoplastic resins used in thermoforming are known for their recyclability and sustainability, meeting the growing demand for environmentally friendly manufacturing practices. These resins can be easily recycled and reused, reducing environmental impact and promoting a circular economy. By utilizing various types of thermoplastic materials in thermoforming, manufacturers contribute to sustainable production and reduce carbon footprints.