PEI GF50: Properties, Machining, and Applications Guide

Polyetherimide (PEI), commonly known by the brand name Ultem, is a high-performance amorphous thermoplastic valued for its exceptional mechanical strength, thermal stability, and flame retardancy. The GF50 grade represents a significant enhancement of base PEI through the addition of 50% glass fiber reinforcement by weight. This composite material offers substantially improved stiffness, dimensional stability, and creep resistance compared to unreinforced PEI, making it suitable for demanding structural and electrical applications in aerospace, automotive, medical, and industrial sectors. This comprehensive guide covers the composition, mechanical and physical properties, processing considerations, typical applications, and comparisons with related grades, providing engineers and procurement specialists with the technical depth needed for material selection.

化学組成と材料組織

PEI GF50 is a composite material consisting of a polyetherimide polymer matrix reinforced with 50% by weight of short glass fibers. The polymer backbone features alternating ether and imide linkages, which contribute to its high glass transition temperature (Tg) and inherent flame resistance without the need for halogenated additives.

Polymer Matrix

The base PEI resin is an amorphous thermoplastic with a Tg of approximately 217°C. Its chemical structure provides excellent resistance to hydrolysis, acids, and aliphatic hydrocarbons. The polymer chain rigidity imparts high tensile strength and modulus even at elevated temperatures, though it also results in relatively low elongation at break.

Glass Fiber Reinforcement

The 50% glass fiber loading is typically achieved using E-glass fibers with a diameter of 10–14 µm and an aspect ratio optimized for injection molding or compression molding. The fibers are treated with a silane coupling agent to enhance adhesion to the PEI matrix, which is critical for stress transfer and mechanical performance. The high fiber content significantly increases the material’s tensile modulus (stiffness) and reduces thermal expansion, but also introduces anisotropy in molded parts due to fiber orientation during flow.

Additives and Fillers

Commercial PEI GF50 formulations may contain small amounts of stabilizers, mold release agents, and colorants. Processing aids are sometimes added to improve melt flow, as the high fiber content increases melt viscosity. No halogenated flame retardants are required because the intrinsic char-forming behavior of PEI provides a UL94 V-0 rating at 0.8 mm thickness.

機械的特性

The addition of 50% glass fiber dramatically alters the mechanical behavior of PEI, increasing stiffness by approximately 3–4 times compared to unfilled PEI. However, the material becomes more brittle, with reduced elongation and impact strength.

Tensile and Flexural Properties

PEI GF50 exhibits a tensile modulus of around 12,000–14,000 MPa and tensile strength of 170–200 MPa at 23°C. Flexural modulus is similarly high, typically 11,000–13,000 MPa. These values are maintained up to 170°C, making the material suitable for load-bearing applications at elevated temperatures. The high modulus reduces deflection under load, which is critical for precision components like mounting blocks used in jigs and fixtures.

Impact and Creep Resistance

Notched Izod impact strength is typically 80–100 J/m, which is lower than unfilled PEI (around 50 J/m for unfilled, but note that unfilled PEI is also notch-sensitive). The glass fibers act as stress concentrators, reducing toughness. Creep resistance is excellent; under a constant load of 14 MPa at 150°C, total strain after 1000 hours is less than 0.5%. This makes PEI GF50 ideal for components that must maintain dimensional accuracy over long service periods.

Fatigue Behavior

Fatigue endurance limit at 10^6 cycles is approximately 40–50 MPa (at 23°C, R=0.1). Fiber orientation significantly affects fatigue life; parts designed with fibers aligned along the principal stress axis show superior performance. For cyclic loading applications, a safety factor of 2–3 is recommended.

物理的・熱的特性

PEI GF50 retains the excellent thermal characteristics of the base polymer while offering improved dimensional stability over a wide temperature range.

Thermal Stability and Glass Transition

The glass transition temperature remains at approximately 217°C, unchanged by fiber addition. Continuous service temperature (UL 746B) is 170°C, with short-term peaks up to 200°C possible. Heat deflection temperature (HDT) at 1.82 MPa is 215°C, only slightly below Tg due to the stiffening effect of fibers. Thermal conductivity is increased to about 0.35–0.45 W/m·K (compared to 0.22 W/m·K for unfilled PEI), aiding heat dissipation in enclosed assemblies.

熱膨張

The coefficient of linear thermal expansion (CLTE) is significantly reduced by glass fiber reinforcement. Typical values are 20–30 × 10^-6 /°C in the flow direction and 40–60 × 10^-6 /°C in the transverse direction (for molded parts). This anisotropy must be considered when designing precision components that will experience temperature fluctuations, such as terminal blocks for electrical enclosures.

Density and Water Absorption

Density of PEI GF50 is approximately 1.60–1.65 g/cm³, higher than unfilled PEI (1.27 g/cm³) due to the dense glass fibers. Water absorption after 24 hours immersion (23°C) is 0.15–0.20%, and equilibrium absorption at 50% RH is 0.5%. This low moisture uptake ensures stable electrical properties in humid environments.

Electrical Properties

PEI GF50 retains the excellent dielectric properties of the base polymer, with the glass fiber reinforcement having minimal impact on electrical performance. The material is classified as a high-performance electrical insulator.

Dielectric Strength and Resistivity

Dielectric strength is typically 18–22 kV/mm (at 1.6 mm thickness, in oil). Volume resistivity exceeds 10^15 Ω·cm, and surface resistivity is greater than 10^14 Ω. These values are maintained up to 150°C, making the material suitable for high-temperature electrical applications.

Dielectric Constant and Dissipation Factor

The dielectric constant (relative permittivity) is 3.5–4.0 at 1 kHz and 23°C, slightly higher than unfilled PEI (3.15) due to the glass fibers. Dissipation factor is 0.001–0.003 at 1 kHz, indicating low energy loss. Comparative tracking index (CTI) is 150–175 V (PLC 3), which is adequate for most industrial applications but may require design precautions in high-voltage environments.

Flame Retardancy and Chemical Resistance

PEI GF50 exhibits inherent flame retardancy without halogenated additives, which is a key advantage for aerospace and mass transit applications.

Flammability Ratings

The material achieves UL94 V-0 at 0.8 mm thickness and V-0 at 1.5 mm. Limiting oxygen index (LOI) is 45–48%, indicating self-extinguishing behavior. Smoke generation is low, with specific optical density (Ds) at 4 minutes of 30–50 (NBS smoke chamber, flaming mode). These properties meet stringent FAA and railway standards for interior components.

Chemical Resistance Profile

PEI GF50 resists most acids (except concentrated sulfuric and nitric), aliphatic hydrocarbons, alcohols, and many cleaning agents. It is attacked by halogenated solvents (e.g., methylene chloride) and strong bases. Continuous exposure to water at 100°C is acceptable, though hydrolysis can occur above 120°C. For medical or food contact applications, the material is USP Class VI compliant and meets FDA requirements for repeated use.

Machining and Fabrication Considerations

PEI GF50 is typically supplied in injection-molded or compression-molded forms. However, secondary machining operations such as drilling, milling, and turning are often required to achieve tight tolerances or add features. The abrasive nature of glass fibers presents unique challenges.

工具および切削条件

Carbide or polycrystalline diamond (PCD) tools are recommended due to the abrasive wear caused by glass fibers. High-speed steel tools wear rapidly. Cutting speeds of 100–200 m/min for milling and 50–100 m/min for drilling are typical, with feed rates of 0.05–0.15 mm/rev. Coolant is not strictly required but can improve surface finish and tool life. Climb milling is preferred to minimize edge chipping.

Dimensional Stability and Stress Relief

Machining can induce residual stresses in the material, leading to warpage or cracking. For precision components like CNC machined camera parts, stress relief annealing at 150–170°C for 2–4 hours is recommended before final machining. The low CLTE of PEI GF50 aids in maintaining dimensional accuracy, but the anisotropic nature of molded stock must be accounted for in the design.

Surface Finish and Post-Processing

Typical machined surface roughness (Ra) is 0.8–1.6 µm. Finer finishes can be achieved with polishing compounds, though the glass fibers may protrude slightly. The material accepts adhesives poorly without surface treatment; corona or plasma treatment improves bond strength for secondary assembly. Painting is possible with epoxy-based primers.

Comparison with Related Grades

PEI GF50 is one of several glass-reinforced PEI grades. Understanding the differences helps in selecting the optimal material for a given application.

PEI GF30 vs. PEI GF50

PEI GF30 (30% glass fiber) offers a balance of stiffness and toughness. It has a tensile modulus of 9–10 GPa and notched Izod impact of 100–120 J/m. PEI GF50 provides higher stiffness and lower CLTE but sacrifices impact resistance. For components requiring both rigidity and moderate toughness, GF30 is preferred; for maximum dimensional stability and load-bearing capacity, GF50 is superior.

PEI vs. PEEK GF50

PEEK GF50 (50% glass-filled polyetheretherketone) offers higher continuous service temperature (240°C vs. 170°C) and superior chemical resistance. However, PEI GF50 is more cost-effective (approximately 30–40% lower material cost) and has better flame retardancy without additives. For applications below 170°C, PEI GF50 often provides the best value.

PEI GF50 vs. PEI Carbon Fiber Grades

Carbon fiber-reinforced PEI (e.g., 30% CF) offers higher tensile modulus (20+ GPa) and lower density, but at significantly higher cost. Carbon fiber grades also provide electrostatic discharge (ESD) protection. PEI GF50 is preferred when electrical insulation is required and cost is a primary concern.

代表的な用途

The combination of high stiffness, thermal stability, and flame retardancy makes PEI GF50 suitable for demanding applications across multiple industries.

航空宇宙・防衛分野

Interior cabin components such as seat parts, overhead bin latches, and air duct covers use PEI GF50 for its low smoke emission and flame resistance. Structural brackets and clips that require high stiffness at elevated temperatures are also common. The material’s compatibility with aerospace cleaning agents is an additional advantage.

Automotive and Transportation

Under-hood components like sensor housings, transmission oil pan baffles, and engine control unit (ECU) enclosures benefit from the material’s heat resistance and dimensional stability. In electric vehicles, PEI GF50 is used for battery module insulators and busbar supports due to its electrical insulation properties.

Medical and Laboratory Equipment

Surgical instrument handles, sterilization trays, and fluidic manifolds utilize PEI GF50 for its ability to withstand repeated autoclave cycles (121°C, 15 psi). The material’s biocompatibility and resistance to cleaning agents make it suitable for reusable medical devices. For precision components like Ultem precision CNC parts, PEI GF50 offers the required accuracy and stability.

Industrial and Electrical

High-temperature electrical connectors, coil formers, and relay bases are typical applications. The material’s low moisture absorption ensures consistent performance in humid environments. Mechanical components such as gears, bushings, and pump impellers benefit from the high stiffness and wear resistance, though lubrication may be required for moving parts.

Tuofa CNC: Precision Machining of PEI GF50

Tuofa CNC, operating as Tuofa CNC Germany, specializes in the precision machining of high-performance engineering plastics, including PEI GF50. With advanced multi-axis CNC milling and turning centers, the company delivers components with tolerances as tight as ±0.01 mm, meeting the stringent requirements of aerospace, medical, and industrial applications.

Machining Expertise for PEI GF50

Our team understands the unique challenges posed by glass-filled materials. We use PCD-tipped tools and optimized cutting parameters to achieve excellent surface finishes while minimizing tool wear. For complex geometries, we employ stress-relief annealing cycles to prevent warpage. Whether you need a prototype or high-volume production, Tuofa CNC ensures dimensional consistency across every part.

Quality Assurance and Certifications

All PEI GF50 parts are inspected using CMM and optical measurement systems. We provide material certification traceable to the resin manufacturer, ensuring compliance with ASTM or ISO standards. Our ISO 9001:2015 certified facility guarantees rigorous process control, and our team can assist with design for manufacturability (DFM) feedback to optimize your component for machining.

Custom Solutions and Rapid Prototyping

Tuofa CNC offers both CNC machining and injection molding services for PEI GF50. For low-volume production or prototyping, we recommend machining from stock shapes to avoid high mold costs. Our engineers collaborate with clients to select the optimal grade and processing method, balancing performance, cost, and lead time. Contact us for a quotation on your next PEI GF50 project.

結論

PEI GF50 is a high-performance glass-reinforced thermoplastic that combines exceptional stiffness, thermal stability, and inherent flame retardancy. Its mechanical properties, including high tensile modulus and low creep, make it ideal for structural and precision components operating at elevated temperatures. While the material presents machining challenges due to fiber abrasiveness, proper tooling and process control enable the production of tight-tolerance parts. Compared to unfilled PEI or alternative high-temperature plastics like PEEK, PEI GF50 offers a cost-effective solution for applications requiring a balance of performance and value. For engineers seeking a reliable partner for PEI GF50 components, Tuofa CNC provides the expertise and quality assurance needed to succeed.