Supplied as an unfilled, unpigmented monofilament, Clariant Natural Thermoplastic Urethane 3D Printer Filament is intended for fused filament fabrication platforms that require translucency, repeated flexural loading, and interlayer adhesion above that of rigid PLA or ABS feedstocks. The absence of chromatic masterbatch produces visibly translucent thin-walled sections and removes pigment agglomerates that can otherwise cause melt-pressure fluctuation through nozzle orifices smaller than 0.4 mm. Procurement specifications typically record nominal filament diameters of 1.75 mm or 2.85 mm, with ovality tolerance within ±0.05 mm verified by laser micrometry rather than single-point calliper readings. Published grade-specific data for the exact Clariant natural TPU configuration is limited; suppliers should provide the lot-specific certificate of analysis before process parameters are frozen. The product is not defined in public commerce by a single rigid copolymer grade designation, and procurement should therefore specify the natural TPU class, filament diameter, Shore hardness, and soft-segment chemistry rather than assume a universal model number.

Thermal Degradation Pathways Are Accelerated Above 230 °C

When the melt zone exceeds 230 °C, urethane bond dissociation becomes kinetically significant. Operation at 240 °C or above for prolonged residence times promotes depolymerization, yellowing, void formation, and molecular weight loss, all of which reduce interlayer toughness. A starting nozzle-temperature band of 210 °C to 230 °C is commonly reported for unfilled Shore 90A-95A TPU filaments, although the exact block temperature must be adjusted for heater block thermal inertia and nozzle alloy. All-metal heat breaks should be monitored for heat creep because the low softening point of TPU permits buckling above the melt zone when the cold-end fan is under-driven. Although the natural unfilled grade is not intrinsically abrasive, hardened steel or ruby nozzle orifices are used on production machines to maintain orifice geometry across repeated material changeovers. Pause cycles longer than 10 min with material held at melt temperature should be avoided; material resident above 15 min is typically purged before the next part. Melt flow-rate data measured at 190 °C with a 21.6 kg load under ISO 1133-1:2022 may fall between 5 g/10 min and 25 g/10 min for unfilled TPU, but this range is not a substitute for grade-specific MFR verification.

At 50 % relative humidity, moisture uptake in TPU filaments can reach 0.2 wt% to 1.0 wt%. Residual moisture above approximately 0.03 wt% at melt processing hydrolyzes ester-based soft segments, generating bubble porosity, uneven extrudate diameter, and a measurable reduction in tensile strength under ISO 527-2. Production drying is typically performed in a desiccant dryer with a dew point at or below -40 °C at 80 °C for 4 h. Polyether-based TPU may degrade oxidatively under the same thermal load, so soft-segment chemistry must be confirmed before drying. Spools are maintained in sealed containers with desiccant and exposed relative humidity below 20 % during printing. Extended builds lasting more than 8 h are typically supplied from an active dry box with continuous relative humidity controlled between 10 % and 15 %.

What Separates an Unfilled Natural TPU from Copolyester and Polyamide 6 Filaments?

Unlike copolyester filament, which offers high stiffness and dimensional stability but frequently fails below 50 % elongation, natural TPU retains a low tensile modulus and elongation at break commonly reported between 300 % and 600 %. Polyamide 6 provides higher tensile strength and abrasion resistance but requires bed temperatures near 100 °C and exhibits moisture-related dimensional movement. Unfilled natural TPU occupies a different property envelope: Shore hardness sits between 85A and 95A, while low-temperature flexibility may be retained below -20 °C when evaluated by ISO 812 or equivalent low-temperature bending methods. Interlayer fusion in TPU is generally stronger than in PLA or ABS because chain interdiffusion proceeds rapidly when the previous layer remains above recrystallization onset, provided the part-cooling fan is limited to 20 % to 40 % of maximum output.

Representative unfilled TPU values and common rigid feedstock values are compared below. These are not Clariant-specific values; supplier certificate data supersedes the ranges.

Functional prototypes that must tolerate repeated flexural or impact loading are printed from this class of TPU: dust bellows, cable grommets, vacuum cups, sealing lips, and low-pressure fluid connectors. Direct-drive extruders with a constrained filament path are preferred because the low column strength of Shore 95A TPU causes buckling inside unconstrained Bowden tubes when retraction distances exceed 2 mm. Print speeds for Shore 85A-95A feedstock are generally restricted to 15 mm/s to 40 mm/s, with layer heights of 0.1 mm to 0.2 mm and nozzle diameters from 0.4 mm to 0.6 mm. For parts printed at 0.2 mm layer height, a bed temperature of 40 °C to 60 °C with a glass or polyetherimide bed covered by a thin polyvinyl alcohol release film improves first-layer adhesion without excessive part-removal stress. Enclosure temperature is held below 35 °C because higher ambient heat reduces cooling efficiency and increases surface tack.

Regulatory Status Under REACH, RoHS, and Food-Contact Evaluation Protocols

For a natural TPU filament placed on the European Economic Area market, REACH registration obligations apply under EC No 1907/2006 for the constituent monomers, stabilizers, lubricants, and melt-processing aids. The absence of heavy-metal pigments supports simplified RoHS documentation under 2011/65/EU and its delegated directives, but RoHS compliance remains matrix-level and must include all intentional additives. Prototype fabrication for medical devices may require testing of the printed article according to ISO 10993-5 and ISO 10993-10; a general industrial TPU filament is not automatically medical-grade, and supplier change-control documentation may be unavailable. For repeated food-contact articles, migration testing under Regulation (EU) No 10/2011 or resin-specific status under FDA 21 CFR 177.1680 must be evaluated for the final printed component, because fused filament fabrication surfaces contain porosity that can retain cleaning agents. Public documentation for the Clariant natural TPU configuration does not establish food-contact or medical certification; raw material statements should be obtained from the supplier before regulated use.

After conditioning at 23 °C and 50 % relative humidity for 88 h according to ISO 291 or ASTM D618, printed coupon batches are tested under ISO 527-2 at a crosshead speed of 50 mm/min. Filament-aligned XY coupons typically retain greater elongation than Z-oriented tensile bars because the layer interface represents the weakest fracture path. Shore hardness measurements under ISO 868 with a 1 kg dead load are taken on plaques with a minimum thickness of 6 mm to avoid substrate effects. Abrasion resistance of TPU components is evaluated using ISO 4649 or DIN 53516 because Shore hardness alone does not rank abrasion performance.

When Filament Buckling Occurs in Bowden Extruders

In Bowden feed systems, filament buckling is the dominant process failure for TPU with Shore hardness below 95A. The combination of a long filament path, high retraction distance, and minimal guide-tube clearance produces helical deformation that is not corrected by raising extruder stepper current alone. Retraction distance should be reduced to 0 mm to 2 mm, retraction speed limited to 10 mm/s to 20 mm/s, and travel moves programmed to avoid crossing open cavities where nozzle pressure can pull material from the melt zone. A direct-drive carriage with a constrained dual-gear filament-grip mechanism reduces slip and provides consistent feed at 15 mm/s to 40 mm/s. Extruder step skipping on a 1.75 mm filament under 0.4 mm nozzle backpressure is an early indicator that melt temperature, flow rate, or nozzle geometry requires adjustment before filament seizure occurs.

Incoming QC records spool-to-spool rheological drift through melt flow-rate measurement under ISO 1133-1:2022 and diameter mapping over at least 10 m of continuous filament. Batch acceptance limits for unfilled TPU are commonly set at MFR variation not exceeding ±20 % of the certified value, diameter standard deviation below 0.03 mm, and ovality below 0.05 mm. Storage above 30 °C can block filament layers through compression set of the spool winding; first-use drying should be repeated after any interval exceeding 30 days at uncontrolled humidity. Process operators record residual moisture before each build using coulometric Karl Fischer titration because gravimetric drying loss alone is insufficient to detect hydrolysis-relevant moisture below 0.05 wt%.