GEHR Plastics FIL-A-GEHR PPSU is an unfilled polyphenylsulfone monofilament for fused filament fabrication. The product designation identifies the material as PPSU within the FIL-A-GEHR series; typical spool diameters are 1.75 mm and 2.85 mm, and the batch certificate records diameter, ovality, and net mass. The filament is a high-temperature amorphous engineering grade, not a drop-in replacement for PLA, PETG, or ABS, because the hot end, build plate, and chamber must be rated for sustained temperatures that exceed the limits of low-cost fused-filament hardware. The material is used for prototypes, tooling, and short-run production parts that require dimensional stability after repeated thermal cycles, resistance to aqueous cleaning agents, or steam-sterilization compatibility.

Compared with other FIL-A-GEHR grades, PPSU moves the processing window from 200–250 °C for general-purpose amorphous filaments to 360–390 °C. This change is not limited to the heater setpoint; it affects the thermistor type, heat-break material, chamber insulation, and part-cooling strategy. Build plates and motion components adjacent to the bed must tolerate 120–160 °C surface temperatures. These requirements are the main practical boundary between PPSU and lower-temperature filaments on the same production floor.

Thermomechanical Profile and Comparative Resin Data

Polyphenylsulfone is a high-Tg amorphous thermoplastic. The resin class shows a glass-transition temperature near 220 °C and a heat deflection temperature near 207 °C at 1.8 MPa under ISO 75-2. Published values for unfilled PPSU resin frequently list tensile yield strength around 70 MPa and tensile modulus around 2.3 GPa when measured under ISO 527-2. The elongation at break of molded PPSU is significantly higher than that of PEI and PSU; this is one reason PPSU is used where autoclave cycling creates cyclic stress. Printed tensile values vary with raster orientation, extrusion factor, chamber setpoint, and annealing. A Z-oriented tensile coupon may retain less strength than an X-Y-oriented coupon because interlayer fusion is the limiting boundary; therefore, structural design with PPSU filament should use printed-coupon allowables generated to ISO 527-2 or ASTM D638 rather than resin-supplier data.

The following typical values are compiled from published resin datasheets and should not replace lot certificates; they are supplied to locate the product family among competing high-temperature filament classes.

Against PSU, PPSU retains almost the same tensile yield strength but increases HDT-A from 174 °C to 207 °C, which is significant for parts under static mechanical load in hot-water or low-pressure steam environments. Against PEI, PPSU has lower stiffness and tensile strength but higher elongation and better resistance to repeated autoclave stress cracking. Against PEEK, PPSU is amorphous, processes at a lower hot-end setpoint, and does not require the same high nozzle temperatures of 380–410 °C often used for unfilled PEEK; however, PEEK provides a higher continuous-use ceiling in oxidative environments because of its semi-crystalline morphology and melting point near 343 °C.

What Changes at the Hot End When PPSU Replaces PSU or PEI?

Switching from PSU to PPSU raises the required melt zone temperature. PSU filament may be processed near 330–350 °C, whereas PPSU filament generally requires 360–390 °C at the hot end. The heated bed should be maintained at 120–160 °C, and the build chamber should be held at 80–120 °C to limit anisotropic shrinkage and corner lift. The hot end must use an all-metal heat break, a high-temperature thermistor, and a hardened steel or nickel-plated copper nozzle; PTFE-lined hardware is unusable above 260 °C because liner decomposition begins. On direct-drive production printers, a retraction starting value of 1.5–3.0 mm at reduced speed is often used to control ooze, but the exact setting is machine-specific and should be tuned with a calibration tower. Build-plate adhesion is usually promoted with a high-temperature polyimide or PEI film; polypropylene or PET build liners are not dimensionally stable at these setpoints. A chamber pre-soak of 15–20 min after reaching setpoint before starting the print is observed to reduce frame-to-bed temperature offset and improve first-layer registration.

Because PPSU lot viscosity can shift, the extrusion line should record melt pressure and hot-end temperature as process parameters. A thermocouple inserted at the nozzle block is more reliable than an internal thermistor at temperatures above 350 °C; high-temperature thermistors may show setpoint drift of several degrees. A nozzle between 0.4 mm and 0.8 mm is generally used; smaller nozzles increase backpressure and may require a lower feed rate. When switching from PSU to PPSU, users should increase hot-end temperature by at least 20–30 °C while reducing print speed to avoid delamination. Active part-cooling fans should be disabled or kept below 10–20 % duty because PPSU layer-to-layer fusion is impaired by rapid surface quench. A heated chamber is the primary control for warp. Open-frame machines without heated enclosures are not suitable for moderate-to-large PPSU parts because ambient drafts produce interlayer cracking at the sidewall; if a machine cannot hold 80 °C chamber temperature, part size should be limited to small coupons and evaluated for delamination.

Spool conditioning is the primary production variable after machine calibration. PPSU resin exhibits a 24-hour water absorption near 0.37 %; printed articles exposed to ambient humidity above 60 % RH may absorb enough moisture to produce steam popping and reduced Z-axis strength. A desiccant or vacuum dryer at 120–135 °C for 4–6 h with a dew point below −40 °C is required before the first use of a new spool. Dry storage below 10 % RH prevents re-moistening during long production runs. If a spool remains on the machine for more than 8 h in an uncontrolled room, re-drying is recommended before continuing with structural parts. The failure mode generated by wet PPSU filament is not merely cosmetic; hydrolysis can reduce interlayer fusion and create notch-sensitive zones near sharp corners. In a production environment, the drying protocol should be combined with a moisture analyser or weight-loss balance on a sampled length of filament to verify residual moisture below 0.05 % before starting a qualified build.

When Steam Sterilization Is Part of the Service Cycle

PPSU resin is widely used in reusable medical devices because it tolerates autoclave exposure at 121 °C or 134 °C without the same stress-cracking sensitivity shown by many transparent amorphous polymers. However, steam-sterilization compatibility of a printed part is not inherited from the resin alone. Delamination sites at layer boundaries can allow water ingress, and a poorly fused PPSU print may microcrack after 20–50 autoclave cycles even though a molded part would survive hundreds. Test coupons should be autoclaved in the intended orientation and inspected for surface change under magnification per the device protocol. If the application is regulated, the final article may require biocompatibility assessment under ISO 10993-5 and ISO 10993-10, and food-contact status should be verified against the specific resin grade notification rather than assumed from PPSU's generic chemical class. REACH Regulation (EC) No 1907/2006 and RoHS Directive 2011/65/EU declarations are supplier-issued for the filament; they do not automatically extend to the printed article after colourants or support materials are used.

Chemical compatibility of PPSU is generally broader than polystyrene and ABS in dilute acids, bases, and many aqueous disinfectants, but it is not universal. Immersion in concentrated strong oxidizing acids, certain halogenated aromatic solvents, methylene chloride, or polar aprotic solvents can soften or stress-crack the polymer. Compatibility testing should be performed under the exact use concentration and temperature, and machined or printed samples should be loaded at the same stress level as the finished assembly. Printed parts may be stress-relief annealed after support removal. The amorphous polymer does not crystallize; the operation reduces frozen-in flow orientation. Typical profiles use 170–190 °C for 1–2 h with ramp rates of 0.5–1.0 K/min. Parts should be supported to avoid creep, and tight-tolerance bores should be re-measured after annealing.

For incoming inspection, filament should be checked for diameter, ovality, surface roughness, and foreign inclusion. A multi-axis laser micrometer can track diameter and ovality along the spool; extrusion tension should be controlled to avoid filament buckling that appears as periodic diameter reduction in rigid high-temperature filament. Because PPSU is rigid and may exhibit spool memory, unwind path friction should be reduced on Bowden systems; a direct-drive extruder with a constrained filament path is preferred. Published data for this specific filament in high-pressure or high-cycle dynamic applications is limited; validation programs should include part-level testing in the final assembly rather than extrapolating from resin grade alone.