Mechanical Recycling of a Short Carbon Fiber Reinforced Polyamide 6 in 3D Printing: Effects on Mechanical Properties.

Mechanical recycling of Fused Deposition Modeling 3D printing materials is very attractive for the circular economy. In this paper, the tensile properties of a virgin and a one-time-recycled short carbon fiber reinforced polyamide, coming from 3D printing scrap and failed parts, were evaluated. Anisotropy was taken into account properly by using characterization methods that are typical of composites. Rheological properties were obtained with a parallel plate rheometer in oscillatory mode, and thermal properties were investigated based on thermogravimetric analysis and differential scanning calorimetry. A decrease in the average molecular weight of the recycled material, indicated by the rheological measurements, induced brittleness. Nevertheless, the stiffness and yield strength of the 3D printed parts made with the recycled material were higher than those made with the virgin one. Since this behavior could not be explained based on an increase in crystallinity or a relevant decrease in the void content, a feasible explanation is proposed with an increase of the interlayer and intralayer adhesion quality. In any case, the recycled polyamide filament can be successfully reused in Fused Deposition Modeling 3D printing, even when significant mechanical properties are required, but attention must be paid to a certain decrease in ductility.