Ensinger TECAFIL PEEK VX natural is an unfilled polyetheretherketone filament supplied on spools with a nominal diameter of 1.75 mm. The grade is based on a virgin PEEK polymer and is intended for fused filament fabrication where high-temperature dimensional stability, chemical resistance and low halogen content are specified. Unlike carbon-fibre-reinforced PEEK, the VX natural material contains no conductive filler, which alters melt viscosity, interlayer adhesion and nozzle wear. Processing occurs at melt temperatures between 375 °C and 410 °C, with the exact setpoint dependent on hot-end length, nozzle diameter and print speed. These conditions exceed the thermal limits of standard polyetherimide and polysulfone filaments, requiring an all-metal hot end, a bed temperature of 130 °C to 160 °C, and a heated chamber to manage crystallisation shrinkage in deposited roads.

Spooled PEEK absorbs moisture from ambient air; exposure at relative humidity above 60 % can generate extrusion defects if the material is not dried. Forced-air drying at 150 °C for 3 h to 4 h or vacuum drying at 120 °C for 4 h to 6 h reduces moisture to below 0.02 %. A high-temperature spool is required because polycarbonate or ABS spool sidewalls can soften at these drying temperatures. Drying should not be performed in an uncontrolled oven without air exchange because hydrolytic degradation at the melt stage produces a loss of molecular weight that manifests as reduced interlayer strength and increased melt fracture.

On production equipment, the unfilled natural PEEK filament is routed through a direct-drive extruder with a hardened steel or wear-resistant nozzle having a bore between 0.4 mm and 0.6 mm. Although the unfilled grade is less abrasive than carbon-fibre-reinforced PEEK, brass nozzles are not rated for continuous operation above 300 °C and are rejected for this application. A heated build chamber maintained between 80 °C and 150 °C is used to reduce the cooling rate of each deposited road. If the chamber remains below 80 °C, the thermal gradient between the melt and the surrounding air can induce curl at part corners and delamination in sections taller than 30 mm. Printing on a PEI or PEEK bed at 150 °C improves adhesion; release may require thermal cycling of the bed rather than mechanical prying at the bonding interface.

What Property Values Are Reported for Unfilled PEEK Filament in ISO 527-2 and ISO 75-2 Testing?

Mechanical and thermal property expectations for the TECAFIL PEEK VX natural grade are based on unfilled PEEK base-polymer datasheets. The values in the following table are moulded-specimen data, not printed-coupon values, because fused filament fabrication introduces orientation, voids and layer interfaces that alter the final mechanical response.

Printed-coupon data for this specific filament configuration are process-dependent. In the X-Y build plane, tensile strength and elongation may approach moulded values when a high chamber temperature and low void content are maintained; however, Z-direction tensile properties are typically lower because interlayer adhesion is governed by diffusion across the surface of the previously deposited road. For acceptance testing, printed specimens should be prepared according to ISO/ASTM 52900 terminology and tested with ASTM D638-14 or ISO 527-2 after conditioning at 23 °C and 50 % relative humidity. Published data for the Z-direction tensile strength of this specific grade is limited, particularly for raster angles other than 0°/90°.

The unfilled natural grade has a coefficient of linear thermal expansion on the order of 45 × 10⁻⁶ K⁻¹ to 55 × 10⁻⁶ K⁻¹ below the glass transition and a higher value above it. This property distinguishes it from carbon-fibre-reinforced PEEK, where the filler reduces the coefficient of linear thermal expansion and can provide a closer match to aluminium in some tooling applications. In semiconductor fixtures and inspection tooling, the unfilled grade is selected when an electrically insulating surface is required and when the presence of carbon filler could produce point-to-point resistance variations.

When Carbon-Fibre-Reinforced PEEK Replaces Unfilled Natural PEEK in Stiffness-Limited Components

Substitution of TECAFIL PEEK VX natural by a carbon-fibre-reinforced PEEK grade changes the mechanical design envelope. The carbon-filled material reports higher tensile and flexural modulus values and lower elongation at break; depending on filler loading, tensile modulus can be 2 to 4 times higher than the unfilled grade, while elongation at break can decline to below 2 %. The unfilled natural grade is therefore used when the part is ductility-limited, when the application requires an electrically insulating surface, or when abrasive wear of nozzle bores and extruder gears is a cost constraint. It is not selected when static-dissipative surface resistivity is required or when the structure must be stiffness-driven at elevated temperature.

Compared with polyetherimide filament, the PEEK VX natural material has a higher heat deflection temperature and superior resistance to aggressive solvents, but its melt-processing window is narrower and the spool cost is higher. Compared with polyphenylene sulfone, the PEEK grade offers lower moisture absorption and better dimensional stability in hot, humid environments; however, PPSU operates at lower hot-end temperatures and remains easier to process on less specialised equipment. The selection between these polymers is not determined solely by heat resistance. In chemical environments containing chlorinated solvents or hot polar aprotic fluids, PEEK is preferred; in applications where repeated steam sterilisation is required and maximum tensile elongation is not critical, the unfilled PEEK grade is also a candidate.

The unfilled natural VX grade is not recommended for prolonged contact with concentrated sulfuric acid, concentrated nitric acid, or halogenating oxidisers at elevated temperature because aromatic ring sulfonation, nitration, or oxidative degradation can occur. It resists hydrolysis in hot water and saturated steam better than many amorphous high-temperature thermoplastics, but printed parts with high void content may exhibit increased moisture uptake compared with fully dense machined PEEK components. The polymer matrix itself has a low saturation moisture uptake of approximately 0.5 %, but FFF porosity can raise the measured weight increase of printed coupons.

Sterilisation Compatibility and Regulatory Compliance Boundaries

The unfilled PEEK grade is used in medical and pharmaceutical tooling where repeated steam sterilisation is performed. Printed parts should be annealed before autoclave exposure because deposition-induced residual stress can relax during the first thermal cycle and cause warpage. A sterilisation cycle at 134 °C for 3 min to 5 min is below the heat deflection temperature of the base polymer at 0.45 MPa, but local stresses in load-bearing features can still produce distortion. Published cycle-life data for this specific filament configuration are limited above 20 autoclave cycles; validation of printed medical devices therefore requires testing on the finished part.

Food-contact and medical-device compliance cannot be claimed from the filament alone. The converter is responsible for migration testing, residual monomer and degradation product assessment, and process validation. In pharmaceutical tooling, the unfilled grade is preferred over carbon-filled PEEK because the absence of carbon fibre simplifies cleaning validation and lowers the risk of particulate release from abraded surfaces. In surgical guide and fixture applications, the base polymer may be selected after a screening cytotoxicity evaluation to ISO 10993-5, but the final printed geometry, sterilisation method and cleaning process define the biocompatibility of the finished part.

Drying and Annealing Parameters Shift the Printed Crystallinity Window

In the annealing step, printed TECAFIL PEEK VX natural parts are held below the melting temperature to increase crystalline order and reduce residual stresses from the deposition process. A forced-convection oven set between 200 °C and 220 °C for 2 h to 4 h is used with steel or ceramic support plates; thin unsupported sections can distort if the holding temperature exceeds the heat deflection temperature of the printed part under its own fixture load. Slow cooling through the range from 300 °C to 160 °C permits secondary crystallisation, while rapid quenching from the melt produces a lower crystallinity and a lower elastic modulus in the final part.

Differential scanning calorimetry according to ISO 11357-3 is used to confirm the melting peak and crystallisation onset temperature of dried feedstock because thermally degraded PEEK can show a depressed melting temperature and a broadened crystallisation peak. The presence of moisture during melt processing has a more immediate effect on interlayer adhesion than on bulk thermal properties; hydrolytically degraded extrudate may exhibit melt fracture, increased die swell, and reduced z-strength. Offline melt flow rate measurement according to ISO 1133-1 can be used to compare spool lots, but the viscosity of unfilled PEEK is high enough that a standard melt flow test at 400 °C with a 5 kg load may produce limited flow; the result should be interpreted as a lot-to-lot comparison rather than an absolute processing specification.

In semiconductor wafer-handling and test-socket applications, the low-charge virgin PEEK grade is preferred over carbon-filled variants because the surface remains electrically insulating. Machined PEEK has historically been used for chemical-resistant fixtures in aqueous cleaning tools; the filament form allows replacement parts to be printed directly into conformal geometries without long-lead machining. FFF tooling in this context is limited by layer porosity and by a service ceiling near the heat deflection temperature under load, not by the melting temperature of PEEK. Load-bearing fixtures should be evaluated by ISO 75-2/A rather than by short-time tensile data.

In downhole and chemical-process equipment, the material is selected where exposure to hot hydrocarbon liquids, sour gas, or aqueous methanol requires a semi-crystalline polymer that resists swelling and stress cracking. Unfilled PEEK has low moisture uptake, but printed components with internal voids may entrap fluid and produce localised pressure-driven blistering if the part is not sealed. Published data for this specific filament configuration is limited for high-pressure sour-gas exposure, and qualification tests such as NORSOK M-710 or customer-specific autoclave exposure should be run on printed coupons with the production raster orientation. The process limitations of high-temperature filament, including the need for heated-chamber hardware and predrying before processing, remain the primary operational boundary for this product.