To increase the applications of FDM (fusion deposition modeling) 3D printing in electronics, it is necessary to develop new filaments with good electrical properties and suitable processability. In this work, polymer composites filament-shaped with superior electrical performance based on polylactic acid (PLA) carbon nanotubes and lignin blends have been studied by combining solution mixing and melt blending. The results showed that composites achieve electrical percolation from 5 wt.% of nanotubes, with high electrical conductivity. Moreover, the introduction of a plasticizing additive, lignin, improved the printability of the material while increasing its electrical conductivity (from (1.5 ± 0.9)$·$10⁻⁷ S$·$cm⁻¹ to (1.4 ± 0.9)$·$10⁻¹ S cm⁻¹ with 5 wt.% carbon nanotubes and 1 wt.% lignin) maintaining the mechanical properties of composite without additive. To validate lignin performance, its effect on PLA/MWCNT was compare with polyethylene glycol. PEG is a well-known commercial additive, and its use as dispersant and plasticizer in PLA/MWCNT composites has been proven in bibliography. PLA/MWCNT composites display easier processability by 3D printing and more adhesion between the printed layers with lignin than with PEG. In addition, the polyethylene glycol produces a plasticizing effect in the PLA matrix reducing the composite stiffness. Finally, an interactive electronic prototype was 3D printed to assess the printability of the new conducting filaments with 5 wt.% of MWCNT.

Material extrusion additive manufacturing is increasingly popular but requires new materials to expand its industrial applicability. This study compares the effects of two bio‐fillers (lignin and spent coffee grounds (SCG)) in a bio‐polymer matrix, polylactic acid (PLA). The bio‐fillers aim to enhance the sustainability of the resulting composites, tune their physical properties (rheology, thermal stability, mechanical resistance and water absorption) and improve 3D‐printability by reducing the temperature at the nozzle. The composite with 15 wt.% SCG exhibited an elongation at break of 22.95% (vs. 8.42% for PLA), a printing temperature of 180°C (vs. 215°C for PLA) and a water absorption after 6 weeks immersion in water of 18.77 wt.% (vs. 5.04 wt.% of PLA), suggesting applications like hydroponic farming. Moreover, small amounts of SCG protected the composite against thermo‐oxidative degradation during extrusion, while lignin enhanced the thermal stability of the composite. Highlights: 15 wt.% SCG improved PLA ductility (elongation at break 22.9% vs. PLA's 8.4%). Lower printing temperature (180 vs. 215°C for PLA) was achieved with 15 wt.% SCG. SCG protects composite from thermo‐oxidative degradation. 15 wt.% SCG in PLA absorbs 18.77% water after 6 weeks (vs. 5.04% of PLA). Lignin boosts thermal stability of PLA composite.

In this work, three bio‐based additives, lignin, spent coffee grounds (SCG), and oil extracted from SCG (Ox‐SCG) were proposed as dispersant agents for multi‐walled carbon nanotubes (MWCNT) in a polylactic acid (PLA) matrix. The resulting materials' microstructure, degradation, thermal stability, rheological behavior, mechanical performance, electrical conductivity, and suitability for 3D printing (fused granular fabrication) were analyzed. The incorporation of the additives significantly strengthened the conductive network, while improving the material interlayer adhesion, especially with SCG. The electrical conductivity increased from 0.2E ⁻¹ S/cm (PLA/MWCNT) to 2.6E ⁻¹ S/cm (PLA/MWCNT/SCG). After studying the physical–chemical properties of the materials, functional strain gauges with two‐ and three‐arm geometries were 3D printed with the best formulation (PLA/MWCNT/SCG). Gauge factors of 0.23 and 1.03 were achieved for the two‐ and three‐arm designs, respectively, demonstrating increased sensitivity with added complexity. Finally, a proof of concept for an accelerometer was developed using the half‐bridge strain gauge setup, integrated with a custom electronic acquisition system.