Lehvoss LUVOCOM 3F PAHT 9825 NT is an unfilled, natural-colour nylon feedstock developed specifically for fused filament fabrication and direct extrusion additive manufacturing systems. The PAHT portion of the designation identifies a heat-stabilised high-temperature polyamide matrix, while the 9825 NT suffix identifies the natural unfilled grade within the LUVOCOM 3F melt-processed thermoplastic portfolio. The product is supplied as a monofilament in nominal diameters of 1.75 mm and 2.85 mm, with controlled ovality and diameter tolerance for consistent volumetric feed in Bowden-drive and direct-drive toolheads. Published manufacturer data describe the base polymer as a polyamide 6/66-based system; the formulation contains heat stabilisers intended to extend melt residence time and reduce oxidative chain scission during hot-end hold at temperatures between 250 °C and 280 °C. Because the material is unfilled, nozzle abrasion is lower than with carbon-fibre-reinforced polyamides, but the stiffness is correspondingly lower and the printed part remains electrically non-conductive.

Before extrusion, the filament should be dried in a forced-air or vacuum dryer at 80 °C for 4–8 h. Target residual moisture is below 0.05 wt%; drying air with a dew point of −30 °C or lower is preferred. Moisture above this threshold produces steam porosity at the nozzle, reduces melt viscosity, and weakens interlayer boundaries. The heated build plate should be held at 80–100 °C, with a chamber temperature of 40–60 °C to reduce residual stress on large flat sections. Initial parameter development on a 0.4 mm hardened steel nozzle at 30–60 mm/s and layer heights of 0.15–0.25 mm provides a stable starting envelope for XY-plane tensile specimens. Z-axis interlayer strength must be developed separately because semicrystalline solidification and chain orientation create anisotropic mechanical behaviour in thin walls.

How Melt Residence Time and Feedstock Moisture Affect Interlayer Fusion in PAHT 9825 NT

Melt residence time is a critical variable because the amide linkage in polyamide 6/66 undergoes hydrolytic and oxidative degradation when heated in the presence of water or oxygen. The heat-stabiliser package in PAHT 9825 NT shifts the onset of measurable degradation, but it does not eliminate the requirement for dry feedstock. Degradation proceeds by two competing pathways. Hydrolytic chain scission dominates when moisture is present; random amide bond cleavage lowers number-average molecular weight and weakens interlayer adhesion. Oxidative degradation dominates in dry but oxygen-rich hot ends above 260 °C, producing chromophores and, eventually, gel particles. The stabilised formulation suppresses the oxidative pathway but cannot protect against grossly wet feedstock. Processing with a dew-point-controlled dryer and an inert feed path is therefore a process control rather than a material property.

At a setpoint of 260 °C, moisture levels above 0.10 wt% can produce hydrolytic chain scission and lower molecular weight sufficiently to reduce weld-line strength at the interlayer boundary. The maximum continuous hot-end residence time should be kept below 15–20 min during stable extrusion. After a pause longer than 10 min, a purge of 20–30 mm of material should be completed before deposition resumes. On production-scale direct-drive systems with all-metal hot ends, intermittent clog formation during extended runs is commonly associated with degraded polymer residue at the heat break or with spool moisture reintroduced after drying. A sealed dry spool holder with desiccant and a hygrometer reading below 10 % RH is an effective control for long builds. Shear thinning behaviour typical of polyamide 6/66 allows deposition through a 0.4 mm nozzle at moderate backpressure. If nozzle pressure becomes unstable, the first troubleshooting step is verification of residual moisture and filament diameter, not increasing extruder temperature beyond 280 °C, because excessive temperature accelerates degradation and increases emission of low-molar-mass volatiles.

On manufacturing lines using a 0.6 mm nozzle and 0.25 mm layer height, unsupported overhangs begin to show surface defects above 45° unless support structures and cooling fan speeds are adjusted for the hotter processing window. A 0.3 mm Z-gap is typically used for breakaway support interfaces to balance support removal force against underside surface finish. Batch-to-batch feedstock variation in the filament diameter beyond ±0.05 mm is a more common cause of under-extrusion than hot-end temperature error when the spool is stored outside a dry box. For unfilled polyamide FFF parts, Z-direction tensile strength is often 50–70 % of XY-direction strength because polymer diffusion across the weld plane remains incomplete. Published data for this specific configuration on overhang fatigue and long-term chemical exposure are limited; application validation is required.

Semicrystalline solidification shrinkage for polyamide 6/66 is typically in the range of 1.0–1.5 % linear. On large flat parts, shrinkage anisotropy between the build plate, chamber, and free surfaces creates residual tensile stress at the part edges. A heated plate above the glass-transition temperature and slow cooling after build reduce warp-induced delamination. For parts thicker than 6 mm, reducing infill density from 100 % to 40–60 % may be necessary to limit internal shrinkage voids.

Representative dry-state mechanical and thermal values reported under standard polyamide test protocols are summarised in the following table. Conditioned values at 50 % RH will show lower modulus and higher elongation because absorbed water acts as a plasticizer. Lot-specific values should be verified against the current manufacturer datasheet before tooling dimensioning.

Comparative Mechanical and Thermal Boundaries Against PA12 and Carbon-Filled Nylons

Compared with unfilled PA12, PAHT 9825 NT has a higher dry-state heat distortion temperature and tensile modulus, but higher moisture uptake. Typical unfilled PA12 HDT/B values are around 90 °C, while PAHT 9825 NT is reported near 180 °C under ISO 75-2/B. The difference is significant for underhood housings or process equipment covers that see short-term temperature excursions. Compared with short-carbon-fibre polyamide compounds, the unfilled PAHT 9825 NT has lower stiffness, lower abrasion resistance, and higher elongation; it also avoids the galvanic coupling and conductive path that carbon fibre can introduce in metal assemblies. Density is lower than carbon-filled grades, which often exceed 1.20 g/cm³. Against an impact-modified PA6, the PAHT grade shifts service temperature upward but may have lower notched impact toughness at sub-zero conditions; the specific grade selection should be made with conditioned impact data from notched Charpy tests.

Within the LUVOCOM 3F range, the PAHT 9825 NT material occupies the unfilled high-temperature nylon position. Glass-fibre-reinforced grades provide higher flexural modulus and lower thermal expansion, but increase nozzle wear and produce rougher side-wall surfaces. Carbon-fibre-reinforced grades provide higher stiffness and electrostatic discharge characteristics, but they reduce elongation and require hardened steel or ruby nozzle bores. The unfilled natural grade is therefore selected when thermal resistance, moderate stiffness, and non-conductive behaviour are required together.

Typical use cases include functional prototypes, bracketry, covers, and tooling fixtures that require better elevated-temperature resistance than PA12 but do not require the stiffness of a fibre-filled grade. The material is also used for short-run production of non-conductive housings where carbon-fibre grades are excluded because of electrical or galvanic concerns.

If an Application Requires Dimensional Stability Above 150 °C Without Fibre Reinforcement

For brackets, sensor housings, and underhood fixtures that must survive short-term temperature excursions above 150 °C, the unfilled PAHT 9825 NT grade is a candidate only when the applied tensile stress remains below the temperature-dependent yield envelope. The dry-state HDT/B value near 180 °C is a short-term thermal deformation indicator, not a continuous load-bearing limit. Creep testing according to ISO 899-2 at the intended service temperature and load percentage should be performed. Published data for continuous use above 150 °C in a load-bearing configuration for this exact grade are limited; a prototype programme using specimens from at least three production lots is recommended to quantify batch-to-batch variation in creep modulus and interlayer fracture energy. The absence of carbon fibre avoids galvanic coupling in aluminium assemblies and permits radio-frequency transparency in sensor or radar brackets, but the unfilled grade does not provide the stiffness of a fibre-filled polyamide.

Printed parts made from PAHT 9825 NT are not supplied with a blanket food-contact approval. If repeated food-contact service is intended, migration testing under Regulation (EU) No 10/2011 or FDA 21 CFR 177.1500, as applicable, must be conducted on the finished printed part because porosity, colourants, and post-processing agents influence compliance. REACH and RoHS conformity should be confirmed with the manufacturer for the specific spool lot. The material should not be combined with acidic or amine-based cleaning agents at elevated temperature without compatibility testing, because polyamide 6/66 can undergo environmental stress cracking or accelerated hydrolysis in acidic media above 80 °C. The spools should be returned to sealed containers with desiccant immediately after use; prolonged exposure to ambient humidity above 60 % RH can raise moisture content to levels that require re-drying before the next build.