The effect of carbon fiber content on physico-mechanical properties of recycled poly(ethylene terephthalate) composites additively manufactured with fused filament fabrication

The combination of recycled fiber reinforcement with recycled polymer as a feedstock material for extrusion-based additive manufacturing creates an opportunity for a more sustainable material use. In this study, recycled short carbon fibers were combined with recycled poly(ethylene terephthalate) (PET) to obtain carbon fiber-reinforced PET filaments via melt extrusion. The carbon fiber content of the extruded filaments ranged from 0.4 to 40.7 wt%. The molar mass and the degree of crystallinity after processing were determined to evaluate the influence of the extrusion process on the physico-chemical and mechanical properties of the reinforced PET filaments. Furthermore, pressure-volume-temperature measurements were carried out to investigate the influence of the carbon fibers on the shrinkage of the semi-crystalline PET. Samples were printed and their superior mechanical properties, including a 390% increase in tensile modulus, were confirmed via tensile testing. Analysis via X-ray micro-computed tomography indicated that the fiber length reduced with increasing fiber content. The high degree of fiber alignment that was observed in the extruded filaments, was slightly reduced after deposition. Scanning electron microscopy data showed that fiber pull-out was the governing failure mechanism, indicating a weak interface between the carbon fibers and the matrix. The results show the potential of extrusion-based additive manufacturing to valorize recycled PET and recycled carbon fibers.