Using Lignin and Spent Coffee Grounds as Bio‐Additives in 3D ‐Printable Poly Lactic Acid/Multi‐Walled Carbon Nanotube Composites for Advanced Electronic Applications

ABSTRACT 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.