Aircraft Cabin Brackets Shift from Machined PEKK to Annealed Unfilled PEEK Prints

In low-volume aerospace interior programs, Evonik INFINAM 9359 F is processed on high-temperature fused filament fabrication platforms to produce brackets, ducting adapters, and cable clamps that replace machined PEKK or aluminum components in non-primary structural zones. The grade is supplied as unfilled PEEK filament and is printed at a nozzle setpoint between 400°C and 430°C, a heated build plate held between 150°C and 160°C, and a build chamber maintained at 130°C to 150°C, depending on the machine's maximum temperature capability and part cross-section. The critical processing conflict is crystallinity management: if the chamber temperature drops below the PEEK glass transition temperature of approximately 143°C during deposition, the melt quenches into an amorphous condition, producing parts with lower heat deflection temperature and reduced chemical resistance; if the chamber temperature exceeds the upper practical limit of 150°C on machines with insufficient thermal shielding, the part may soften and lose geometric tolerance. After printing, annealing at 200°C for 2 h in a circulating-air oven raises the crystallinity to a level sufficient for dimensional stability above the glass transition, but parts with a wall thickness above 6 mm require stepwise cooling at no more than 10°C per hour to prevent thermal stress cracking.

Compliance for cabin interiors is anchored to 14 CFR Part 25.853, which requires flammability testing of materials installed in occupied compartments. Unfilled PEEK resin typically carries a UL 94 V-0 rating at 1.5 mm thickness; however, a fused filament fabrication part cannot inherit the resin rating automatically because interlayer boundaries and microvoids alter the burning behavior. Aircraft programs therefore require coupon testing on printed, annealed, and surface-finished specimens according to the relevant vertical or horizontal burn test, often in conjunction with smoke density testing under ASTM E662 or far-field conditions specified in the OEM qualification plan. For mechanical validation, ASTM D638-14 Type IV tensile specimens machined from printed blanks provide ultimate tensile strength and tensile modulus values, while ASTM D790-17 flexural tests evaluate bracket stiffness. The unfilled grade does not contain carbon fiber or glass fiber, so electrostatic discharge is not inherent; components in fuel-vapor zones must be assessed for static dissipation or replaced with carbon-filled PEEK variants where charging is uncontrolled.

Terminal components include cabin divider brackets, in-flight entertainment frame adapters, air supply duct flanges, and electrical standoffs. Published production data for this specific configuration is limited, but process experience on high-temperature FFF systems indicates that delamination at the Z-axis is the dominant failure mode when the chamber temperature is below 100°C or when the filament absorbs moisture before extrusion. Filament spools must be dried at 150°C for a minimum of 5 h in a desiccant dryer with a dew point no higher than -40°C, particularly when the storage relative humidity exceeds 60%, because residual moisture hydrolyzes the polymer during deposition and creates bubble defects that reduce interlayer adhesion. Batch-to-batch filament diameter variation beyond ±0.05 mm changes melt pressure; an oversized filament increases backpressure in the hot end and can cause skipped steps on the extruder drive, producing intermittent under-extrusion. Dimensional accuracy on a 200 mm-long bracket after annealing is influenced by anisotropic shrinkage; toolpaths should be compensated non-uniformly, with greater compensation in the build direction than in the X-Y plane, though published correction factors for this specific filament are limited and must be established on the target machine.

What Makes Unfilled PEEK Acceptable for Autoclave-Processed Surgical Instruments?

The selection of Evonik INFINAM 9359 F for surgical instrument handles, orthopedic trial devices, and fluid manifold housings depends on sterilization stability and the absence of extractable leachables rather than on short-term mechanical strength alone. PEEK is a semi-rigid aromatic polyether ether ketone; its hydrolytic resistance allows repeated steam sterilization at 134°C and 2.1 bar without the hydrolytic embrittlement observed in amorphous thermoplastics such as polycarbonate or polysulfone. Published data for the base polymer class show that PEEK retains a high proportion of its tensile properties after hundreds of autoclave cycles, but FFF-fused parts must be free of connected porosity because residual steam can condense inside voids and cause subsurface delamination or microbial entrapment. The filament is printed with a 0.4 mm hardened nozzle at 400°C to 430°C, with a chamber temperature above 130°C to ensure interlayer fusion and a bed temperature of 150°C to 160°C; any layer separation visible at the surface is cause for rejection because it creates a biologic entrapment site. Production-scale printing of surgical components has shown that brass nozzles release trace copper and zinc under prolonged 430°C operation; hardened steel or titanium nozzles are used to control extractable metals.

Regulatory acceptance in invasive or patient-contact use is demonstrated through a combination of ISO 10993-5:2009 for cytotoxicity, ISO 10993-10:2021 for skin sensitization and irritation, and USP Class VI systemic injection testing, depending on the device classification. Evonik technical documentation for INFINAM 9359 F references biocompatibility evaluation according to ISO 10993-5 and USP Class VI; nevertheless, final device validation remains the responsibility of the device manufacturer because printing parameters, post-processing, and cleaning agents alter the surface chemistry. The unfilled composition avoids glass-fiber or carbon-fiber surfaces that could abrade and generate particulate matter in a cleanroom environment.

Terminal products include reusable scalpel handles, clamp bodies, sterilization trays, and positioning fixtures. The processing chain includes printing in a controlled environment, support removal with mechanical cutting rather than solvent dissolution, annealing at 200°C for 2 h, and ultrasonic cleaning with deionized water followed by drying at 120°C for 4 h. Dimensional tolerances for printed surgical instruments are typically ±0.1 mm for features below 50 mm, but the liquid absorption after autoclaving is low enough that critical dimensions shift less than the layer resolution. Instruments intended for repeated autoclave use should not be exposed to alkaline cleaners above 60°C because concentrated sodium hydroxide degrades the PEEK surface over time, which increases roughness and reduces fatigue strength.

Across downhole completion tools, wireline housings, and electrical connector insulators, the combination of sour gas, high pressure, and temperature cycling drives material qualification beyond standard mechanical property data. Evonik INFINAM 9359 F is unfilled PEEK, so continuous service at 150°C to 200°C is within the polymer class range, but the printed component's maximum allowable working temperature is governed by the glass transition at approximately 143°C and the degree of crystallinity achieved during post-processing. Components such as sensor brackets, coil bobbins, and connector bodies are printed on high-temperature FFF systems with the chamber at 140°C to 150°C, then annealed at 200°C for 2 h to stabilize creep behavior. The degree of crystallinity is measured by differential scanning calorimetry according to ISO 11357-3; double melting peaks indicate incomplete recrystallization and can correlate with lower interlayer strength. The absence of fiber reinforcement avoids galvanic coupling and reduces abrasive wear against mating metal surfaces, but it also lowers tensile modulus relative to carbon-filled PEEK, which must be considered in buckling-sensitive slender parts.

Chemical qualification in oil and gas service is usually performed according to ISO 23936-1:2009, which addresses thermoplastics for downhole use. Exposure to methane, brine, and H2S-containing gas at elevated pressures requires rapid gas decompression testing, and while PEEK as a class resists explosive decompression better than most elastomers and many thermoplastics, printed layers can initiate cracking at voids if the interlaminar bond is incomplete. Typical measurement of bond integrity uses cross-sectional microscopy and tensile testing in the Z-direction according to ASTM D638-14 after exposure. In systems with H2S partial pressures above 1 bar, the end user must validate the specific printed geometry because hydrogen sulfide can alter the PEEK surface and reduce ductility over time, although published data for this specific filament configuration is limited.

Terminal products include downhole sensor housings, cable clamp bodies, seal backup rings, and instrument pressure barriers. The processing limitation is thick-section warpage: sections above 20 mm require reduced infill density or heated annealing with stepwise cooling to avoid internal residual stress that accelerates environmental stress cracking in the presence of hot brine. Filament storage before printing must ensure moisture content below 0.02%; in humid field-service support environments with relative humidity above 60%, drying at 150°C for at least 5 h is mandatory. Because unfilled PEEK has high chemical resistance to aliphatic hydrocarbons and aromatic solvents, components are compatible with crude oil and most drilling fluids, but they are not recommended for exposure to concentrated nitric acid or concentrated sulfuric acid at temperatures above 50°C.

When Wafer Handling Requires Trace-Metal Control Without Carbon-Fiber Loading

When wafer handling requires trace-metal control without carbon-fiber loading, unfilled PEEK filament is processed into wafer combs, CMP retainer rings, test sockets, and chemical distribution components. Evonik INFINAM 9359 F is suited to these applications because it contains no carbon fiber or talc filler that would contribute particle shedding or metallic contamination. The filament is printed on high-temperature FFF equipment with a hardened nozzle at 400°C to 430°C and a chamber at 150°C where the entire build volume can be maintained; machines that cannot sustain at least 130°C across the part envelope produce inadequate interlayer fusion and are unsuitable for semiconductor process contact parts. After printing, components are annealed at 200°C for 2 h and then cleaned in an ultrasonic bath with deionized water of resistivity 18 MΩ·cm to remove residual organic films and loose polymer particles.

Vacuum outgassing is screened according to ASTM E595, which measures total mass loss, collected volatile condensable materials, and water vapor regained. Fully crystallized PEEK often shows total mass loss below 1.0% and collected volatile condensable materials below 0.1%; however, FFF parts can exceed these values if moisture or low-molecular-weight degradation products are trapped in the porous interlayer regions. Consequently, printed semiconductor components are baked at 250°C for 4 h in a clean oven to drive off volatile species before installation in process chambers. The thermal excursion during this bake is above the glass transition and can slightly relax residual stress, so the final machining passes are performed after the bake step to preserve flatness and hole position.

Terminal products include wafer combs for 300 mm carriers, test socket insulators, and robotic end-effector pads. The absence of carbon fiber limits continuous service temperature to below 260°C and rules out high-load structural parts in etch chambers, but unfilled PEEK provides electrical insulation and lower particle generation than fiber-filled compounds. In filament production, the PEEK resin is processed on twin-screw extruders with an L/D ratio of 40:1 at melt temperatures between 360°C and 400°C; this production route influences the degree of hydrolysis and color, and each spool must be dried uniformly before vacuum sealing. In the print room, a dust-controlled environment is required because airborne conductive particles can embed in the soft interlayer surface and compromise electrical insulation.

In chlor-alkali, acid-transfer, and high-purity solvent processing, unfilled PEEK is used for valve seats, pump wear rings, flow meter housings, and flange gaskets because it combines chemical resistance with creep resistance at temperatures up to 150°C in aqueous acids. Evonik INFINAM 9359 F is printed as a near-net shape blank, then machined on tight-tolerance contact surfaces to reach the flatness and surface finish required for sealing. The material is unfilled, so it is not recommended for high sliding wear against metal shafts at elevated load; carbon-fiber-filled PEEK grades are required when the pressure-velocity product exceeds the unfilled polymer's design limit, which is dependent on the mating surface and operating temperature but is often below 0.1 MPa·m/s for unlubricated continuous sliding.

Chemical compatibility is evaluated by immersion testing under ISO 175. Unfilled PEEK retains strength after prolonged exposure to hydrochloric acid, phosphoric acid, acetic acid, sodium hydroxide, and aliphatic hydrocarbons. Concentrated sulfuric acid above 50°C and concentrated nitric acid cause oxidation and must be avoided, as do halogenated solvents at high temperatures that can induce environmental stress cracking. Fluorine, chlorine, and other strong oxidizing agents attack the aromatic ring structure. For pump and valve components that handle aqueous acids at temperatures below 100°C, printed and annealed INFINAM 9359 F can often replace fluoropolymers where mechanical stiffness is insufficient, but the upper working temperature for unfilled PEEK under load is lower than that of fiber-reinforced PEEK compounds.

Typical terminal products include diaphragm pump check valves, gear pump wear plates, valve stem sealing rings, and flow meter internal parts. Processing requires a high-temperature FFF platform with filament dried at 150°C for 5 h and a build chamber maintained at 140°C to 150°C; printed parts are annealed at 200°C for 2 h to minimize residual stress and then machined to final tolerances. In thick sections above 25 mm, the annealing step must include a slow cooling rate of 10°C/h from 200°C to below 100°C; failure to do so can produce thermal stress cracks that propagate in hot dilute sulfuric acid service. Because unfilled PEEK contains no conductive filler, it can be used in contact with aggressive media without the possibility of creating galvanic cells, but the exclusion of fiber also reduces creep resistance at temperatures above 180°C, and design verification under sustained load must account for viscoelastic deformation.

High-Voltage Connector Insulation and Partial Discharge Stability in Unfilled PEEK

High-voltage connector inserts, coil bobbins, and busbar supports are printed from Evonik INFINAM 9359 F when the design requires a dielectric material that can withstand exposure to transformer oil, silicone potting compounds, and operating temperatures above 120°C. Unfilled PEEK has high dielectric strength, but the printed structure, with its layer lines and possible microvoids, can reduce the effective breakdown strength relative to solid injection-molded PEEK. High-voltage components therefore require proof testing at the final thickness and under service conditions. ASTM D149-20 is used to measure dielectric strength of solid insulating materials; printed specimens should be tested both parallel and perpendicular to the layer plane because anisotropy can cause the breakdown strength to differ between build directions.

Partial discharge testing under IEC 60270 is performed on printed connector insulators intended for medium-voltage service. Unfilled PEEK exhibits a comparative tracking index of approximately 150 V to 175 V when tested to IEC 60112, which is moderate and means the material is not suitable for heavily polluted outdoor creepage paths unless the surface is protected by geometry or coating. The thermal index of unfilled PEEK is above 240°C in molded form according to UL 746B; however, UL certification applies to the resin and not to the FFF process, so printed parts require separate evaluation. Flammability of the base resin is normally tested to UL 94 V-0 at 1.5 mm, but printed and annealed samples must be evaluated on the final part thickness.

Process conditions for electrical insulators are similar to other high-temperature PEEK applications: nozzle at 400°C to 430°C, bed at 150°C to 160°C, chamber at 130°C to 150°C, and annealing at 200°C for 2 h. Thin walls below 1 mm tend to curl at the bed surface if the chamber is below 100°C. In oil-filled systems, the material can operate in transformer oil at temperatures up to 180°C, but it should not be combined with amine-based epoxy hardeners at elevated cure temperatures because aggressive amines can reduce molecular weight and lead to surface cracking. Terminal products include high-temperature terminal blocks, connector bodies, high-voltage cable clamps, and insulated standoffs. Because unfilled PEEK is not electrically conductive, it does not provide static dissipation; where static charge accumulation is a concern, a carbon-filled PEEK grade or a conductive coating is required.