Ensinger TECAFIL PEEK EV natural is a 1.75 mm diameter monofilament of unfilled polyetheretherketone produced for fused filament fabrication and other material extrusion processes. The product designation separates the grade from filled TECAFIL PEEK products: natural refers to the absence of carbon fibre, glass fibre, graphite, polytetrafluoroethylene, and inorganic pigments, while EV identifies the unfilled filament/extrusion grade within the Ensinger portfolio. Published process and mechanical data for this exact product configuration remain limited; therefore, the values reproduced here are drawn from publicly reported data for unfilled PEEK measured according to ISO and ASTM methods and should be verified against the manufacturer lot datasheet. The nominal diameter of 1.75 mm is commonly paired with a diameter tolerance of ±0.05 mm and an ovality target below 0.04 mm, values that reflect modern laser-controlled filament extrusion lines rather than a universal specification. The natural colour provides an electrically insulating, halogen-free baseline for chemical-processing, semiconductor, oil-and-gas, medical, and aerospace components, provided that the fused filament fabrication system can maintain the required thermal environment.

Polyetheretherketone belongs to the polyaryletherketone family and is synthesised from 4,4′-difluorobenzophenone and hydroquinone, yielding an aromatic backbone with ether and ketone linkages. The repeat unit contains three aromatic rings, two ether linkages, and one ketone linkage; this chain rigidity is responsible for the glass transition near 143 °C and the crystalline melting point near 343 °C. In the melt, PEEK exhibits shear-thinning behaviour. The natural unfilled grade has no reinforcing fibres to increase melt viscosity, so extrusion force through a 0.4 mm nozzle tends to be lower than for filled grades, but the melt itself remains thermally sensitive above 420 °C.

Semicrystalline order in a fused filament fabrication part is not an intrinsic constant. It depends on cooling rate, bed temperature, chamber temperature, and local toolpath reheating. Slow cooling from above 300 °C permits spherulitic growth; rapid cooling associated with small parts and unheated chambers may suppress crystallinity and lower the upper service temperature. The natural grade is particularly transparent to X-ray inspection because it lacks carbon-fibre absorption; this can simplify void detection and fibre orientation assessment, although voids remain detectable by high-resolution CT.

Why Is Pre-Drying a Threshold Requirement Rather Than an Optional Step?

Polyetheretherketone is not strongly hygroscopic under ambient storage. Equilibrium moisture absorption for unfilled PEEK is generally below 0.5 % by mass at 23 °C and 50 % relative humidity, and the 24 h water-absorption value according to ISO 62 is typically 0.1–0.5 %. Despite this low bulk value, fused filament fabrication makes the material vulnerable to moisture-induced hydrolysis. The melt temperature of PEEK is 343 °C; at the hot end, the combination of temperatures above 360 °C, melt residence time, and the high surface-to-volume ratio of a 1.75 mm filament permits even 0.1–0.3 % moisture to produce chain scission. The resulting failure mode on production-scale equipment is rarely visible as steam bubbles alone. It appears as a fluctuating extrusion line width, intermittent nozzle clogging, reduced transverse tensile strength, and an increase in melt flow rate after thermal cycling. Pre-drying protocols reported for PEEK filament require 120–150 °C for 3–5 h in a circulating-air or vacuum dryer, followed by sealed storage with desiccant if ambient relative humidity exceeds 60 %. The safe threshold is therefore not a fixed moisture content; it is a function of melt temperature, residence time, and local humidity. For interrupted runs longer than 2 h in an uncontrolled environment, re-drying is the standard corrective action.

Bulk moisture measurements by ISO 62 can understate the risk because condensation forms on the filament surface and spool core before it equilibrates through the filament cross-section. On machines without a heated filament chamber, humid air entering the feed path can deposit moisture on the outer layer, producing localised hydrolysis while the core remains dry. An actively heated build chamber above 70 °C reduces uptake during printing but does not remove water already present in the feedstock. The outer diameter of 1.75 mm is small enough that the diffusion distance from surface to centre is short; this accelerates both moisture absorption and drying compared with injection-moulding pellets, but it also means that a dried spool can regain surface moisture rapidly when exposed to air at relative humidity above 60 %. Published data for the water regain rate of this specific PEEK EV natural filament is limited.

When Nozzle Temperature Falls Below 360 °C, Interlayer Fusion Collapses

Despite the melting peak at 343 °C, a nozzle setpoint of 350–355 °C is usually insufficient for acceptable interlayer strength in PEEK fused filament fabrication. The previous layer surface cools below the crystallisation onset before the next road is deposited, particularly when layer times exceed 15 s. The interface then develops as a low-entanglement boundary with reduced Z-direction strength. On production-scale material extrusion equipment with a 0.4 mm nozzle, 0.2 mm layer height, and print speeds below 40 mm/s, sustained melt temperatures of 375–420 °C are typical for unfilled PEEK. At the upper end, thermal degradation competes with fusion. Above 420 °C, longer residence times can produce gel formation, chain branching, and an increasing melt viscosity that further destabilises extrusion. This conflict between interlayer fusion and chain degradation creates a working window of approximately 360–420 °C, but the true optimum depends on hot-end residence time, nozzle thermal stability, chamber temperature, and raster geometry. Because published data for this specific TECAFIL PEEK EV natural 1.75 mm filament at different nozzle setpoints is limited, empirical verification with a temperature tower and transverse tensile specimens according to ISO 527-2 or ASTM D638-14 is required before production release.

The build plate and chamber are part of the same fusion-control system. A bed below 120 °C often produces insufficient first-layer adhesion and edge curl as crystallisation proceeds. Heated bed settings of 150–200 °C are common for unfilled PEEK, but the adhesion surface must survive these temperatures. Polyimide film can be used up to roughly 200 °C, while carbon-reinforced silicon or textured polyimide plates may tolerate higher local temperatures but introduce surface roughness limits. An actively heated chamber above 70 °C reduces the thermal gradient between the deposited melt and the surrounding air, thereby lowering the delamination tendency. Post-print annealing at 200 °C for 2 h is sometimes applied to raise crystallinity and dimensional stability; however, it can cause dimensional change of 0.3–1.0 % and reduce ductility at high strain. The decision to anneal should therefore be made against the end-use load case rather than as a universal step.

On production-scale machines, unfilled PEEK feedstock has been observed to wear brass nozzles at a faster rate than lower-temperature thermoplastics, but less than filled PEEK. A hardened steel or high-temperature steel nozzle is commonly selected for 1.75 mm PEEK not because the natural grade is abrasive but because the same machine often alternates between filled and unfilled runs. The melt pump and extruder gear must be cleaned to avoid carbon-fibre residues from previous filled-filament jobs contaminating the natural grade.

Representative Unfilled PEEK Property Bands Used for Accept/Reject Decisions

The table below is a design-input summary for unfilled PEEK, not a substitute for lot-specific data for Ensinger TECAFIL PEEK EV natural.

These values are characteristic of unfilled PEEK in moulded or dense bulk form. Fused filament fabrication introduces layer interfaces and void populations that can reduce tensile properties, particularly in the Z-direction. The natural PEEK EV grade is therefore specified not only by filament diameter but by the printing environment needed to converge toward these bulk values.

A change in filler identity alters the dominant failure mode.

Comparisons among unfilled, carbon-fibre-filled, and glass-fibre-filled PEEK filament grades are summarised below. The filled-grade values are representative literature ranges and may not correspond exactly to the Ensinger TECAFIL equivalents.

Compared with polyetherimide, PEEK EV natural has a higher melting point and broader chemical resistance but requires a more demanding build environment. PEI may be processed at nozzle temperatures near 350–380 °C; PEEK generally requires 375–420 °C. PEKK and PEEK are chemically similar, but PEKK may exhibit different crystallisation kinetics and can be processed at somewhat lower temperatures depending on the isomer ratio. PPSU offers steam sterilisation resistance but lower tensile modulus than unfilled PEEK. The unfilled natural grade is electrically insulating, whereas carbon-fibre-filled PEEK is conductive or static-dissipative in many configurations. That difference determines whether the printed part can be placed near energised conductors or used as a dielectric barrier.

Dimensional tolerance control starts at the hot-end entry.

Filament diameter and roundness are decisive because feed force in fused filament fabrication is transmitted through a restricted hot-end entry. If diameter varies along the spool by more than ±0.05 mm, the extruder stepper may underextrude or overextrude. Ovality above 0.04 mm creates an asymmetric pressure distribution inside the heat break. Production-scale filament lines use two-axis laser scattering gauges and melt pumps to control diameter; the output is wound onto spools with controlled tension. Incoming inspection for this 1.75 mm PEEK EV natural product typically includes multiple diameter measurements along the spool, a roundness check at 20–25 °C, and visual confirmation of no surface contaminants. The natural grade is particularly sensitive to carbon black contamination, because carbon particles are visible and can compromise electrical insulation.

Compliance claims for PEEK materials may include food-contact, medical-use, and chemical-control obligations. Unfilled natural PEEK grades are frequently assessed under REACH, RoHS, FDA 21 CFR for food contact, and USP Class VI for medical applications, but the existence of a grade on the market does not by itself constitute a certification for all end uses. For this specific TECAFIL PEEK EV natural filament, the end user must verify that the lot-specific datasheet and the final printed part meet the relevant regulatory requirement. Published data for the printed part in body-contact devices is limited; validation must include post-processing, cleaning, and sterilisation effects.

Typical application contexts for the natural grade include manifolds, chemical-processing fittings, semiconductor wet-bench fixtures, electrical insulators, medical instrument handles, and oil-and-gas components where an unfilled PEEK baseline is needed. In all cases, the material selection is constrained by FFF-specific anisotropy: the Z-direction tensile strength of an FFF PEEK part may be only 30–60 % of the in-plane value depending on raster and chamber conditions. The natural unfilled grade has no carbon reinforcement to obscure X-ray inspection, which is a practical advantage over carbon-filled grades in void detection.

Operational boundaries are defined as much by the final part porosity as by the polymer itself. Concentrated sulfuric acid, concentrated nitric acid, and strong oxidising environments attack PEEK at elevated temperatures; exposure above 200 °C in oxidative media may embrittle the surface. In sour oil-and-gas service, PEEK has broadly accepted resistance to hydrogen sulphide and hydrocarbon mixtures, but interlayer voids may compromise sealing and permit fluid intrusion. Published data for this specific filament configuration under multicomponent sour gas, pressurised water, or sterilisation cycling is limited; validation on printed tensile bars and pressure-test coupons is required. The material is not recommended for use in contact with molten alkali metals or with fluorinating agents. No single processing condition or material property can guarantee fitness for end use.