The product designated Ensinger TECAFIL PEEK VX blue — 1.75 mm filament — is an unfilled polyetheretherketone monofilament for fused filament fabrication. The VX designation places the material in the virgin unfilled TECAFIL PEEK range, with blue pigmentation introduced to provide visual contrast. Polyetheretherketone is a semicrystalline polyaryletherketone having a crystalline melting point near 343 °C and a glass transition temperature near 143 °C when measured by differential scanning calorimetry according to ISO 11357-1/-3. These values impose a processing window that excludes ordinary low-temperature desktop extrusion systems. The product is used in oil and gas sealing prototypes, semiconductor wafer handling fixtures, aerospace tooling, and medical device housings, where the printed part must retain dimensional stability and mechanical usefulness after exposure to hot water, steam, or aliphatic hydrocarbons. A direct-drive all-metal hot end, a heated bed, and a heated build chamber are required for reliable deposition.

Because the filament is made from high-molecular-weight PEEK, it is hygroscopic enough to require aggressive drying before extrusion. The blue pigment does not reduce the moisture sensitivity. In the absence of adequate drying, absorbed water converts to steam at melt temperatures above 360 °C and creates bubble defects, hydrolysis-induced molecular-weight loss, and reduced interlayer strength. The sections below address the thermal boundary conditions, benchmark data, and the differences between this unfilled blue grade and reinforced or amorphous alternatives.

If the Build Chamber Is Held Below the Crystallization Window of TECAFIL PEEK VX Blue

PEEK solidifies through a crystallisation process that operates between the glass transition near 143 °C and the melting point near 343 °C. The fastest spherulitic growth is commonly reported in the range 170–200 °C. When a deposited bead cools quickly in an unheated chamber, crystallisation may be incomplete before the next layer is applied. Low-crystallinity material has a density closer to 1.26 g/cm³, whereas the semicrystalline state approaches 1.30 g/cm³. The resulting density increase during delayed cold crystallisation produces non-uniform shrinkage. On parts with wall thickness above 5 mm or long unsupported corners, this shrinkage appears as corner lifting, part warpage, or interlayer cracking.

A circulating-air chamber held at 80–150 °C slows the cooling rate and allows the material to build crystallinity while the part is being printed. The chamber must not only reach the setpoint but also hold spatial gradients across the print area below ±5 °C. On machines without a heated chamber, reliable PEEK deposition is limited to small cross-sections; even then, z-axis tensile strength may be lower than xy-plane strength because interfacial polymer diffusion is time- and temperature-dependent. Printed PEEK parts that are later annealed at 200 °C for 2 h in a circulating-air oven may undergo further crystallisation and dimension change. Such parts should be annealed on a fixture, because z-axis shrinkage can reach several tenths of a millimetre per 10 mm of thickness.

The thermal control requirement is not a cosmetic issue. In fused filament fabrication, the interlayer boundary is a weakness plane. If the chamber is below 80 °C, the previously deposited layer surface can cool below the glass transition before the next layer arrives, reducing molecular interdiffusion at the interface. The result is a part that appears solid but fails prematurely in z-direction tensile testing according to ISO 527-2. For this reason, processing recommendations for TECAFIL PEEK VX blue on industrial equipment always include closed-loop chamber heating rather than passive enclosure retention alone.

Thermal Benchmarks, Moisture Desorption, and Filament-Handling Limits

Table 1 reports typical values for unfilled PEEK resin obtained from standard injection-moulded or compression-moulded coupons. These values are not direct guarantees for additively manufactured parts, because fused filament fabrication produces anisotropic solids with raster lines and interlayer boundaries.

An additively manufactured part produced from 1.75 mm stock should not be expected to match the tensile elongation or flexural modulus of an injection-moulded specimen without extensive process testing. The presence of raster-to-raster boundaries and the z-axis interface can reduce tensile elongation and ultimate strength compared with the isotropic reference data. Users generating design allowables should print and test coupons under the same chamber, nozzle, and annealing conditions as the end-use part, using ISO 527-2 for tensile properties and ISO 178 for flexural properties. Published data for this specific blue-pigmented filament configuration is limited; therefore, lot-specific test results from the manufacturer or an independent laboratory are required for critical structural parts.

Thermal analysis of incoming filament is useful for quality control. A first heating scan should show the PEEK melting endotherm near 343 °C and may show a cold-crystallisation exotherm if the filament has been quenched during production. The intensity of that exotherm is a qualitative indication of initial crystallinity. In practice, incoming filament with excessive amorphous content may still print acceptably if the chamber is controlled, but the first layer may require a reduced speed below 15 mm/s to improve bed contact. Drying before printing is mandatory. A residual moisture content above 0.02 wt% is a known threshold for bubble formation in unfilled PEEK extrusion. Circulating-air ovens at 150 °C for 3–4 h or vacuum ovens at 120 °C for 12 h are common drying protocols. Dried spools should be transferred directly to a sealed filament feed box or desiccated holder; open exposure to air at 60 % RH can allow moisture re-absorption within hours. Because the filament is stiff and wound onto spools, inner layers can retain moisture longer than outer layers if the spool is dried as a whole. For this reason, processors often dry individual spool quantities rather than large sealed cartons, and verify dryness with a loss-on-drying balance or a calibrated moisture analyser.

Table 2 gives a starting process window for unreinforced PEEK filament on industrial fused filament fabrication equipment with a heated chamber. The values are industrial process parameters, not product release limits.

The upper nozzle-temperature limit of 400 °C lowers melt viscosity and can improve raster adhesion, but it also shortens the thermal-degradation induction time. The lower limit of 360 °C reduces degradation risk but may produce under-extrusion with nozzle diameters below 0.4 mm. For a 0.4 mm nozzle, low volumetric flow rates are used because the hot-end power budget must maintain melt temperature while the chamber is also heated. Melt rheology is strongly shear-thinning; a small temperature drop in the hot end produces a measurable increase in backpressure and die swell. Because 1.75 mm filament has a smaller cross-section than 2.85 mm stock, feeding force is lower, but the hot end must still melt sufficient volume for a given speed. Direct-drive extruders with a high-torque stepper motor and an actively cooled gearbox are therefore preferred for PEEK.

Feed rollers should be kept below 60 °C; water-cooled or heat-shielded extruder drives are preferred when the chamber is operated above 100 °C. Spool-to-spool variation in pigment dispersion can shift the optimum extrusion multiplier slightly, so a filament diameter check with a two-axis laser micrometer is recommended after each lot change. Ovality above 0.05 mm can cause intermittent under-extrusion because the effective cross-sectional area changes along the spool. Receiving inspection should therefore sample at least three positions per spool and check for tight bends near the hub. As with all semicrystalline high-temperature filaments, part design must account for anisotropic shrinkage. Sharp internal corners create stress concentrations that are amplified by thermal gradients between the top deposited layer and the chamber environment. A sacrificial brim or raft is common for parts with a footprint larger than 50 mm × 50 mm; the raft increases first-layer contact area but leaves roughness on the bottom surface. Soluble support materials are generally not available for PEEK at these chamber temperatures, so support structures must be printed in the same material and mechanically removed.

What Distinguishes Unfilled Blue PEEK Filament from Reinforced Polyetheretherketone?

Carbon-fibre-filled PEEK filament is used when higher stiffness, lower creep, and lower coefficient of thermal expansion are required. A carbon-fibre loading of approximately 30 wt% raises tensile modulus from the unfilled value of 4.0 GPa to a typical range of 20–25 GPa under ISO 527-2. The trade-off is a reduction in elongation at break to low single-digit percentages and an increase in melt viscosity. Glass-fibre-filled PEEK occupies an intermediate position, with tensile modulus often in the range 8–10 GPa and a lower cost than carbon-fibre-filled material. The blue unfilled grade remains electrically insulating and has lower thermal conductivity than carbon-fibre-filled PEEK, making it more useful where thermal isolation or dielectric strength is needed. In abrasive or sliding wear conditions, unfilled PEEK is generally not the first choice; reinforced grades are selected because the fibre reinforcement lowers specific wear rate and reduces creep under high contact pressure.

The coefficient of linear thermal expansion for unfilled PEEK is approximately 50 × 10⁻⁶ K⁻¹ below the glass transition and 110 × 10⁻⁶ K⁻¹ above it when tested according to ISO 11359-2. Carbon-fibre-filled PEEK can show much lower expansion along the fibre direction, sometimes below 20 × 10⁻⁶ K⁻¹. This difference must be considered when a printed PEEK component is joined to a metal housing. The unfilled blue grade has a thermal conductivity near 0.25 W/(m·K), whereas carbon-fibre-filled PEEK may exceed 0.9 W/(m·K) depending on filler content and orientation. These thermal differences influence part-cooling behaviour and can change the optimum chamber temperature.

Compared with amorphous polyetherimide filament, which is processed at nozzle temperatures around 350–380 °C, TECAFIL PEEK VX blue requires a higher or equivalent nozzle setpoint and a more tightly controlled chamber. The semicrystalline polyetheretherketone offers better resistance to hot steam, boiling water, and many aggressive hydrocarbon fluids. This difference is significant in oil and gas fixtures and chemical processing hardware, where polyetherimide may stress-crack under repeated steam exposure. However, the PEEK processing window for interlayer fusion is narrower, and an open-frame machine without a thermal enclosure is not acceptable for consistent results. The blue pigmentation in this product provides visual contrast for part identification and may aid automated optical sorting, but it is not a radio-opaque filler and does not provide metal detectability.

Chemical resistance of unfilled PEEK is broad but not universal. The material is resistant to hot water, steam, aqueous ammonia, methanol, and many aliphatic and aromatic hydrocarbons. Strong oxidising acids can attack the polymer: concentrated sulfuric acid and concentrated nitric acid are known to degrade PEEK, and continuous exposure to chlorine gas or certain strong oxidising solutions at elevated temperature should be avoided. The resistance of a printed part may differ from that of a compression-moulded plaque because internal porosity and raster boundaries can act as permeation pathways. For fluid-contact applications, printed specimens should be tested under the specific chemical, temperature, and pressure conditions rather than relying only on resin compatibility tables.

Regulatory compliance depends on the exact formulation, pigment package, and printing history. Unfilled PEEK resin can be evaluated for biocompatibility under ISO 10993-5 and USP Class VI when the appropriate documented grade is used, but these certifications do not transfer automatically to pigmented filament or to additively manufactured parts. For food-contact applications, the finished printed part must meet the applicable migration limits such as FDA 21 CFR 177.2415 or EU 10/2011. The blue pigment may alter overall migration in certain food simulants and must be assessed on the final part. Aerospace interior applications may require fire, smoke, and toxicity testing to FAR 25.853 or ASTM E662; as-printed surface roughness and internal voids can influence these results. Steam sterilisation at 134 °C is frequently applied to PEEK medical devices, but repeated cycles can produce additional crystallinity and slight dimensional change. A final cleaning and drying step before sterilisation is necessary because residual moisture in surface porosity can create pressure-driven defects during autoclaving.