Development of electrically conductive hybrid composites with a poly(lactic acid) matrix, with enhanced toughness for injection molding, and material extrusion-based additive manufacturing

In this study, we developed electrically conductive nano- and hybrid composites with a poly(lactic acid) (PLA) matrix for different melt processing technologies. We used short carbon fiber and multi-walled carbon nanotube reinforcements to enhance electric conductivity. We prepared the composite compounds with twin-screw extrusion; then the compounds were processed via injection molding and fused filament fabrication. We showed that electric conductivity only slightly increased by when only carbon nanotubes were added to the PLA matrix. However, when carbon fibers were added to the nanocomposites, the higher shear during melt mixing helped the uniform dispersion of the carbon nanotubes, resulting in a highly conductive reinforcement network in the composite. On the other hand, the hybrid reinforcement resulted in higher viscosity, making melt processing difficult and the material also became more brittle. Therefore, we added an oligomeric lactic acid plasticizer to the hybrid composites, and produced specimens by injection molding and 3D printing. The tensile strength increased by 140% and the elongation at break increased by 56%, and at the same time, the electrical conductivity of the material remained at a high level.