Clariant PA6/66-GF20 FR LS using Exolit flame retardant nylon 3D printing filament is a fused filament fabrication grade composed of a polyamide 6/66 copolymer matrix, 20 wt% short glass fibre reinforcement, and a halogen-free organophosphorus flame-retardant package. The filament is supplied in 1.75 mm and 2.85 mm diameters. Intended applications include electrical enclosure prototypes, structural brackets, battery module fixtures, and components requiring stiffness above unfilled flame-retardant polyamide, lower shrinkage than unreinforced nylon, and self-extinguishing behaviour after removal of the ignition source. The material differs from conventional brominated or chlorinated flame-retardant nylon by replacing gas-phase radical-quenching chemistry with a condensed-phase char-forming phosphorus system, thereby eliminating the need for antimony trioxide synergists and reducing the density contribution of the flame-retardant package. Because the matrix is a PA6/66 copolymer, the melt peak is broadened relative to PA66 homopolymer; this improves diffusion across layer interfaces but reduces the maximum crystallinity achieved during cooling.

Drying is not optional. Polyamide absorbs water rapidly; above 0.05 wt% moisture content the steam pressure generated in the nozzle creates voids and irregular filament flow, while hydrolytic chain scission reduces weld strength and can cause audible popping or nozzle drool. A dry-air oven at 80 °C for 4–8 h is adequate for sealed spools opened at 60 % RH; production cells should use desiccant dryers with a dew point of −40 °C or lower. The print temperature is typically 255–275 °C at the nozzle, with a heated bed at 80–100 °C. Because the glass fibre is abrasive, a hardened steel nozzle of 0.4 mm minimum bore or a wear-resistant nozzle such as ruby or PCBN is required; brass nozzles degrade rapidly. For parts larger than 100 mm in the X-Y plane, an enclosed chamber held at 45–60 °C reduces differential crystallisation and corner lift.

Melt viscosity is higher than unfilled flame-retardant nylon because the glass fibre increases shear viscosity at low shear rates. Direct-drive extruders with an all-metal heat break and a melt zone shorter than 4 mm perform better than long PTFE-lined hot ends, which soften above 250 °C and can lose extrusion path concentricity. The volumetric flow limit near 10–12 mm³/s for a 0.4 mm nozzle prevents underheating and steam backflow; higher flow rates call for larger nozzle bores or operation near the upper end of the nozzle temperature range without exceeding 275 °C.

What Limits Continuous Operating Temperature in Exolit-Containing PA6/66-GF20?

The upper continuous-use limit is not set by the heat distortion temperature alone. Under ISO 75-2:2013 Method A at 1.8 MPa, injection-moulded coupons of 20 wt% glass-filled flame-retardant PA6/66 class materials typically fall between 185 °C and 210 °C. Printed specimens frequently give lower values because layer boundaries and void content act as stress concentrators. Continuous exposure at 120–140 °C can initiate oxidative degradation of the polyamide, beginning as yellowing and surface microcracking, particularly in low-infill parts where oxygen can permeate internal channels. The Exolit phosphorus species can interact with thermal stabilisers at prolonged high temperature; therefore any application above 110 °C should be validated with retention of tensile impact or notched Charpy after 1,000 h ageing in air, using ISO 179-1/1eA:2010 and ISO 527-2:2012 specimens printed at 100 % infill.

The Exolit system operates through phosphate ester decomposition to polyphosphoric acid species during combustion. These species catalyse dehydration and char cross-linking in the polyamide matrix, increase the residue fraction, and reduce heat release rate. This is different from gas-phase halogenated systems, which interrupt free-radical oxidation but do not produce the same char yield. As a result, PA6/66-GF20 FR LS can be rated UL 94 V-0 at 1.6 mm in supplier-moulded plaque data, but published data for this exact filament configuration is limited for printed parts thinner than 1.5 mm. Printed wall thickness, infill density, and raster orientation must be validated by UL 94 vertical burning or IEC 60695-2-12 glow-wire testing on final parts before regulatory acceptance.

In contrast to unfilled flame-retardant PA6/66, the 20 wt% glass fibre reduces isotropic mould shrinkage and lowers equilibrium moisture uptake, but creates anisotropic tensile properties. Raster-aligned tensile modulus can exceed transverse modulus by 15–30 %, and notched impact strength in the Z direction is typically only 40–60 % of XY values. Users moving from unfilled flame-retardant nylon should therefore avoid locating snap-fit hooks or threaded insert bosses in the build direction. Compared with a 20 wt% glass-filled non-flame-retardant PA6/66, the Exolit package increases melt viscosity and lowers elongation at break; the nozzle temperature is often raised by 10–20 °C to maintain melt flow. Against a halogenated flame-retardant PA66-GF20, the Exolit grade eliminates halogen-related stress cracking in polycarbonate contact points and reduces smoke density measured under cone calorimetry according to ISO 5660-1:2015.

Compared with flame-retardant PA12, the PA6/66 matrix offers higher stiffness and lower creep at elevated temperature, but higher moisture absorption and lower Z-direction impact resistance. Compared with flame-retardant polycarbonate, the nylon grade provides better resistance to aliphatic hydrocarbons and weak alkalis but requires stricter drying and is not suitable for transparent applications. These differentiators are material-class comparisons; final selection must be based on printed-part testing under the exact electrical, thermal, and mechanical load spectrum.

Table values are representative supplier datasheet ranges for extruded or injection-moulded coupons; printed part values depend on raster angle, infill, chamber temperature, and moisture content and should be verified by lot-specific certificates.

The material’s halogen-free formulation allows simplified documentation under IEC 61249-2-21 for halogen content in components adjacent to printed circuit boards and under RoHS 2011/65/EU annex II, which restricts lead, mercury, cadmium, hexavalent chromium, PBB and PBDE. Compliance must still be confirmed against lot-specific documentation because glass fibre surface sizing and heat stabilisers may contain trace restricted substances. REACH Regulation EC 1907/2006 requires declaration of any substance of very high concern above 0.1 wt%; for most production lots of this grade no SVHC declaration is expected, but incoming material should be checked for harmonised classification.

Where the 3D Printed Layer Boundaries Constrain Flame-Retardant Certification

A common failure occurs when datasheet flame ratings obtained on injection-moulded plaques are transferred to additively manufactured parts without examining void content or interlayer fusion. The layer boundary acts as a low-density plane and can serve as a wicking path for molten polymer during vertical burning, causing drips that lead to UL 94 failure even when the base resin is inherently V-0. Electrical enclosure prototypes should therefore be printed at 100 % infill with alternating rectilinear raster angles separated by 45 °, at least 4 perimeter walls, and perimeter overlap of 0.1 mm or greater. The cooling fan after the first layer should be limited below 30 % to allow interlayer diffusion; excessive cooling produces fine spherulites and weak boundaries.

Printed articles exposed to continuous electrical current require dielectric strength verification according to IEC 60243-1. The glass fibre lowers volume resistivity relative to unfilled material because moisture condenses at the fibre-matrix interface, and conditioning under ISO 291 at 23 °C and 50 % RH for 48 h is required before testing. Just-printed parts may contain less than 0.1 wt% moisture and give misleadingly high dielectric values. In contrast to flame-retardant polycarbonate filament, this nylon grade retains resistance to aliphatic hydrocarbons and weak alkalis but is attacked by strong mineral acids, glycol ether coolant concentrates, and aqueous zinc chloride; such service conditions require sealing or substitution.

Moisture, Fibre Orientation, and Post-Print Annealing

Equilibrium moisture uptake at 23 °C and 50 % RH for a 20 wt% glass-filled PA6/66 typically falls between 1.0 wt% and 1.5 wt%, below unfilled PA6 because the glass phase excludes water but above PA12, which absorbs approximately 0.5–0.8 wt%. Conditioned parts expand by 0.2–0.4 % in the XY plane and 0.4–0.7 % in the build direction, because fibre orientation is least effective across layer boundaries. Post-print annealing at 120 °C for 2 h in dry air can increase crystallinity and relieve residual stress, but unconstrained parts may shrink by 0.5–1.0 %; critical dimensions therefore require annealing fixtures.

The trade-off between flame retardancy and strength is most pronounced at the Z-axis. When bars are printed on edge with the long axis perpendicular to the build platform, ultimate tensile strength can fall below supplier values by 30–50 % because the interlayer weld is the weakest plane. Snap-fit features or clips that must survive repeated assembly should be built in the XY plane and without supports where possible. Annealing improves interlayer strength but reduces impact ductility; for impact-sensitive parts, conditioning at 70 °C for 1 h may be more suitable.

The table is a verification matrix for incoming material and printed-part qualification, not an exhaustive regulatory certificate.

In production cells fitted with direct-drive extruders, hardened steel nozzles of 0.4 mm minimum bore, and actively heated chambers maintained at 50 °C, the dominant failure modes are mechanical rather than thermal: filament buckling when the spool pay-off radius is below 100 mm, and nozzle bore enlargement due to glass-fibre abrasion after 200–300 h of continuous extrusion. Brass nozzles are not suitable for this grade and can wear measurably within 20 h. Layer heights below 0.1 mm are not recommended because short fibre clusters can temporarily bridge the nozzle and produce stochastic clogging. The material is also incompatible with prolonged immersion in aqueous zinc chloride, glycol ether-based coolant concentrates, and strong mineral acids; mechanical fasteners or seals should be specified for these environments.