Effect of carbon nanotubes on mechanical properties of polyamide 12 parts by fused filament fabrication

Polymer parts fabricated by fused filament fabrication (FFF) technique usually exhibit weak and anisotropic mechanical properties, compared with their injection-molded (IM) counterparts. Thus, the evolution of FFF from rapid prototyping into manufacture tool requires three-dimensional enhancement ways for FFF-printed parts. To this end, we develop a series of carbon nanotubes (CNTs)-embedded polyamide 12 (PA12) filaments and investigate the effect of CNTs on the mechanical properties of the FFF-printed PA12 parts. In the direction parallel to the deposited strands, PA12/CNT parts show considerable mechanical reinforcement compared with neat PA12 specimens, including the increase of tensile and impact strength by 18% and 125%, respectively. The marked improvement in impact strength arises from the oriented structures induced by the shear field during FFF process as well as the layer-by-layer microstructure, which provide multiple ways to dissipate impact energy. However, these oriented CNTs and inter-filament voids tend to act as stress concentration points under the tensile stress, thus accounting for a slight increase in tensile strength. In the direction perpendicular to the deposited strands, the FFF-printed PA12/CNT parts also exhibit improved tensile strength, i.e. interfacial weld strength, as CNTs allow the rapid transfer of the thermal energy from the newly-deposited filament to the weld interface and thus provide longer time for molecular interdiffusion. Altogether, the anisotropy in tensile strength of the FFFprinted parts is reduced from 0.36 for neat PA12 parts to 0.28 for PA12/CNT specimens. This work is believed to provide a facile route to overcome mechanical limitations in FFF technique.