B. Bikson, N. Khadse
Avanpore, LLC,
United States
Keywords: PEEK, Fibers, melt spinning, morphology
Summary:
Poly(ether ether ketone) (PEEK) is a commercial thermoplastic polymer with best-in-class thermomechanical properties and is widely used for fiber manufacturing via melt spinning. PEEK fibers are qualified for service in a broad range of extreme environments, including sustained temperatures up to 260 °C and exposure to strong acids and alkalis. PEEK is both radiation resistant and inherently flame-retardant, supporting its use in extreme and safety-critical environments. Its chemical solvent resistance and high service temperature exceed those of all commercially available fibers fabricated from thermoplastic polymers. When used in composite materials, PEEK offers one of the broadest ranges of mechanical performance among high-performance fibers, with elastic moduli as high as ~150 GPa and tensile strengths up to ~2,000 MPa at 23 °C. These values are comparable to or exceed those of PPS fibers and approach those of aramid fibers, while providing substantially higher thermal stability and chemical resistance. UHMWPE fibers exhibit higher tensile strength and modulus, but low melting temperature, poor creep resistance, and limited compressive performance, restricting applicability in high-temperature and load-bearing structural environments. PEEK has significant potential for advanced engineering applications, including aerospace, automotive, high-performance textiles, biomedical devices, and electrical systems. High-strength polymer fibers are widely used in composites due to their high specific strength and tensile stiffness, properties that arise primarily from the alignment of polymer molecular chains. Achieving optimal mechanical performance typically requires very high polymer molecular weight, as demonstrated by UHMWPE. Polymers with high molecular aspect ratios can crystallize into extended-chain morphologies under suitable processing conditions. However, commercially available PEEK exhibits a relatively modest molecular weight and slow crystallization kinetics, which limit the attainable mechanical properties of conventional PEEK fibers. The utilization of PEEK as an advanced high-performance fiber has been further hindered by poor adhesion and wettability resulting from inherently low hydrophilicity. Avanpore has developed several novel technologies that overcome these limitations and enable the fabrication of PEEK-based fibers with a unique and superior combination of performance attributes. First, PEEK blends with selected polyimides form compatible polymer alloys that can be melt-extruded into fibers with enhanced mechanical properties, overcoming intrinsic limitations associated with PEEK’s molecular weight and crystallization behavior. These fibers exhibit high molecular chain aspect ratios and a high degree of crystallinity, enabling the formation of extended-chain morphologies under optimized processing conditions. Post-treatment methods further enhance tensile strength through controlled optimization of crystal size and morphology. Second, Avanpore has developed sustainable, green surface-functionalization methodologies for PEEK fibers that introduce hydroxyl, epoxy, and amino functional groups without compromising fiber morphology or crystalline structure. As a result, the water contact angle is reduced from approximately 89° to below 50°, significantly improving adhesion while preserving intrinsic mechanical properties. Third, PEEK fibers with a core–shell morphology have been developed, in which a dense fiber core is surrounded by a thin porous surface layer of controlled thickness. The porous shell exhibits a mesoporous morphology with a high specific surface area of up to 180 m²/g, imparting adsorption functionality to an otherwise high-strength structural fiber.