Carbon-enhanced thermoplastic polyurethane composites for FFF: Filament extrusion, microstructure, printed-part quality, multifunctional performance, and preliminary piezoresistive response

Thermoplastic polyurethane (TPU) is attractive for material extrusion-based additive manufacturing owing to its elasticity, abrasion resistance, and biocompatibility. However, pure TPU suffers from low stiffness, thermal conductivity, and electrical conductivity, restricting its use in multifunctional flexible sensors and wearable electronics. This study demonstrates a powder-precursor route for producing carbon fiber (CF)-reinforced TPU filaments at loadings of 0-20 wt.%. TPU powder was dry-blended with micron-sized CF powder, extruded into filaments, and 3D-printed via fused filament fabrication (FFF). Scanning electron microscope (SEM) revealed homogeneous CF dispersion, progressive increases in surface roughness ( S a = 36.20 μm), tensile strength, and Young’s modulus. Hardness rose modestly to 93.5 at 20 wt.% CF. Differential scanning calorimetry (DSC) revealed additional CF-dependent crystallization and melting features, consistent with modified hard-segment ordering and a possible heterogeneous nucleation effect. Thermogravimetric analysis (TGA) confirmed enhanced thermal stability (onset decomposition temperature +14 °C at 20 wt% CF). Dynamic mechanical analysis (DMA) indicated reduced damping with increasing CF content. Electrical conductivity exhibited a percolation threshold between 5–10 wt% CF, reaching 12 S/m at 20 wt.%. Hamilton–Crosser modelling predicted an increase in effective thermal conductivity from 0.25 to approximately 0.48 W·m -1 ·K -1 at 20 wt.% CF. The powder-to-filament-to-print workflow enables excellent filler dispersion and tunable multifunctional performance offering promising composites for piezoresistive sensors, soft robotics, and wearable devices.