Ensinger TECAFIL PSU natural – 1,75 mm – Filament Polysulfone is an unfilled amorphous polysulfone filament supplied on 1.75 mm diameter spools for fused filament fabrication. The base polymer is designated PSU under ISO 1043-1 and belongs to the polyarylsulfone family. The natural grade contains no filler or pigment and produces a translucent appearance. Because the polymer chain contains sulfone and isopropylidene groups, the material exhibits a glass transition temperature near 187 °C and a heat deflection temperature of approximately 174 °C under 1.80 MPa when tested according to ISO 75-2 method A. TECAFIL PSU does not show a melting endotherm; solid-state stiffness and creep resistance are controlled by the amorphous glass transition rather than by crystallinity. This characteristic differentiates the product from semi-crystalline PEEK and polyamide filaments, where crystallization history influences shrinkage, chemical resistance, and post-extrusion dimensional change. The filament is intended for high-temperature fused filament fabrication platforms with a hot end capable of sustained operation at 350 °C to 390 °C, a heated bed at 120 °C to 160 °C, and an actively heated build chamber. Melt viscosity is high relative to PLA and PETG, so direct-drive extruders with hardened steel or brass nozzles of 0.4 mm diameter are common industrial configurations; larger nozzle diameters reduce extrusion backpressure.

Primary application contexts include functional prototypes, chemical-resistant fixtures, fluid manifolds, medical device housings, and laboratory equipment subjected to repeated steam or chemical disinfection. The unfilled natural grade is selected when translucency is required or when filler-induced nozzle abrasion and filled-anisotropy are unacceptable. Published mechanical values for TECAFIL PSU are typically generated on injection-moulded test plaques rather than on fused-filament parts. Values obtained from printed components vary with raster orientation, extrusion multiplier, interlayer porosity, chamber temperature, and post-print annealing. Therefore, datasheet values should be treated as upper bounds unless parts are printed with fully dense shells and low interlayer void content.

What Distinguishes Unfilled PSU from PEI and PEEK in High-Temperature Filament Extrusion?

Unfilled PSU occupies a processing temperature band below polyetherimide and polyetheretherketone but above commodity styrenics and aliphatic polyesters. Its heat deflection temperature of 174 °C is lower than typical unfilled PEI at 200 °C to 210 °C and unfilled PEEK at 260 °C to 280 °C. As a result, PSU can be processed on moderate-cost high-temperature FFF systems, but it is not a direct substitute for PEEK in continuous load-bearing service above 180 °C. Compared with PEI, PSU generally shows lower tensile strength and flexural modulus but improved resistance to hot-water hydrolysis and steam-autoclave stress cracking in many fluid-contact applications. Compared with PEEK, PSU shows lower chemical resistance in aggressive aromatic solvents, ketones, and chlorinated hydrocarbons, but requires lower extrusion temperatures and reduced chamber heating. Compared with PLA, PETG, and ABS, PSU offers higher heat deflection temperature and lower creep at elevated temperature, but requires higher bed and chamber temperatures and stricter moisture control.

The single-point values in the table are not FFF part performance data. At 0.15 mm to 0.25 mm layer height and high chamber temperature, xy-direction tensile strength can approach injection-moulded values only when interlayer fusion is complete. Z-direction properties are usually lower because layer interfaces are regions of reduced polymer-chain diffusion. Design allowables for printed load-bearing components should therefore be determined by destructive testing according to ISO 527-2 with specimens cut parallel and perpendicular to the build plane.

When a Heated Chamber Is Absent, Edge-Lifting and Warp Risks Increase

During deposition, the upper layers cool below the glass transition while the lower layers remain hotter. If the chamber is below 80 °C, the thermal gradient across a large-footprint part can generate interlaminar and interfacial stress sufficient to separate the part from the build sheet. The risk scales with build-plate dimensions because the temperature difference between the deposited layer and the part core increases with footprint. Closed-chamber systems are preferred because they maintain a more uniform part temperature during the print. A chamber temperature of 90 °C to 120 °C reduces the difference between the deposited layer and the part core and lowers z-direction thermal strain. Polyetherimide or polyimide build sheets are used because adhesion must survive bed temperatures of 120 °C to 160 °C; untreated glass or low-temperature polymer sheets are generally insufficient for large PSU parts.

Extrusion settings are material-, nozzle-, and chamber-specific. A starting window for a 0.4 mm hardened steel nozzle is extruder temperature 350 °C to 380 °C, bed temperature 140 °C to 160 °C, chamber temperature 90 °C to 120 °C, and print speed 20 mm/s to 40 mm/s. Because PSU is amorphous, no holding time is required for crystallisation; however, the part should remain in the chamber until the chamber cools below 100 °C to reduce warping. Layer height of 0.15 mm to 0.25 mm and extrusion multiplier of 1.00 to 1.05 are typical, but calibration with a single-wall test cube is necessary because backpressure and die swell vary with nozzle wear.

Moisture control before extrusion is a pressure-dependent processing requirement. Polysulfone absorbs water at 23 °C to approximately 0.30 % by mass after 24 h and higher at saturation; at melt temperatures above 350 °C, residual moisture hydrolyses the polymer or flashes at the nozzle, producing splay, voided interlayer boundaries, and diameter swell. The filament should be dried at 120 °C to 140 °C for at least 4 h in a desiccant or vacuum dryer until residual moisture falls below 0.05 %. Spools exposed to relative humidity above 60 % for more than 24 h should be re-dried before extrusion. Sealed storage with desiccant is required for batch-to-batch consistency.

Thermal, Mechanical, and Chemical Resistance Limits for Fluid-Handling and Autoclave Applications

The sulfone backbone provides hydrolytic stability and resistance to hot water, dilute acids, and aliphatic alcohols, which is why PSU is used in fluid-handling and laboratory equipment. However, PSU is not universally solvent-resistant. Ketones, chlorinated hydrocarbons, aromatic solvents, and some esters can cause stress crazing or environmental stress cracking. Exposure to acetone, methylene chloride, or methyl ethyl ketone is a known incompatibility. Steam autoclave exposure at 134 °C for 4 min according to ISO 17665 is generally tolerated by fully dense PSU parts, but FFF porosity can retain water and cause delamination or pressure burst during autoclave heating. Polysulfone resin grades may be compliant with FDA 21 CFR 177.1655 for repeat-contact food-use applications when processed under appropriate conditions; compliance of the final printed part is not automatic because surface roughness, residual stress, and contact geometry can alter extraction behaviour. For medical applications, ISO 10993-5 cytotoxicity testing must be conducted on the finished fused-filament part, not on the raw filament alone.

Compared with glass-filled or mineral-filled polysulfone filaments, the natural unfilled grade eliminates filler and reduces nozzle abrasion, but it also provides lower modulus and higher thermal expansion. Compared with PPSU, the polysulfone product has lower impact strength and lower heat deflection temperature, but it is generally available at lower material cost and requires a moderately lower extrusion temperature. Published data for the specific configuration of TECAFIL PSU natural as printed on high-temperature FFF equipment is limited; qualification should therefore include z-direction tensile testing, autoclave cycling, and chemical immersion tests on the same print parameters intended for production.

On an FFF platform with a 0.4 mm hardened steel nozzle, direct-drive extruder, polyimide build sheet, and active chamber held at 100 °C, the natural PSU filament is typically run with a nozzle set point of 365 °C and a bed set point of 150 °C. The first layer is deposited at 15 mm/s with an extrusion multiplier of 1.10 to ensure adhesion; subsequent layers are printed at 30 mm/s. Under these conditions, xy-direction tensile bars from fully dense infill can reach 60 MPa to 70 MPa, while z-direction tensile bars often remain below 30 MPa unless the part is annealed at 165 °C for 2 h. The main processing failure modes observed on high-temperature FFF cells are nozzle blockage from degraded material, surface splay from wet filament, and edge-lifting from premature chamber opening. These failure modes are reduced by operating at the lower end of the extrusion temperature window, purging after each job, and verifying moisture loss during drying.