Study of the interlayer adhesion and warping during material extrusion-based additive manufacturing of a carbon nanotube/biobased thermoplastic polyurethane nanocomposite

Abstract

A thermoplastic bio-polyurethane from renewable sources (TPU) and the nanocomposite developed by mixing it with carbon nanotubes (CNT) are investigated as potentially adequate for Material Extrusion-based Additive Manufacturing (EAM). Thermal and rheological features are studied from the perspective of their liaisons with printing adequacy and conditions. As predicted by rheology, both samples show good performance in filament elaboration and flow in the nozzle. Warpage is observed for TPU, but not for the nanocomposite, which is due to the effect of CNT nanoparticles on polymer chains dynamics. At the studied printing velocities, interlayer adhesion strength is independent of printing velocity implying that there is no significant chain orientation which can induce changes in the TPU entanglements. The nanocomposite shows a lower welding strength, notwithstanding both have the same chain entanglements density. This is explained by considering that the higher viscosity of TPU/CNT, as compared to TPU, reduces the melt diffusion coefficient.