Fused Granulate Fabrication of Polypropylene Carbon Nanotube Composites: A Preliminary Study

Polypropylene (PP) is a semi-crystalline polymer extensively used for manufacturing end-user parts in a wide range of industries, mainly processed by injection molding (IM). Advancements in Additive Manufacturing (AM) technologies have accelerated the material development process, and polypropylene is now becoming available as filament for Fused Filament Fabrication (FFF). However, PP is still difficult to process with FFF technology due to high volumetric shrinkage and severe warpage. Fused Granulate Fabrication (FGF) is an advanced AM technology that involves direct extrusion of pellets and is well-suited for thermoplastics that are sensitive to thermal degradation or difficult to extrude as continuous filament. The aim of this study is to investigate the printability of polypropylene-carbon nanotube (PP/CNT) composites using the FGF technology. PP/CNT pellets with different CNT loadings (0.5, 1, 3, and 5 wt%) were FGF-printed, and the influence of the CNTs on the dimensional accuracy, inter-layer strength, and mechanical and electrical properties was analyzed. Injection-molded PP/CNT samples were also fabricated, and their mechanical and electrical properties were compared with those of the FGF-printed samples. The experimental results reveal the capability of the FGF technology to manufacture PP/CNT composite parts with high geometric accuracy and good inter-layer bond strength. The FGF samples printed at 0° orientation outperform the IM samples in terms of both tensile strength and elastic modulus. However, the FGF samples exhibit significantly lower strain a break than the IM samples. Remarkably, the electrical conductivity of FGF samples with 5 wt% CNTs was about three orders of magnitude higher than that of the IM samples. This study contributes to expanding the potential of using PP/CNT composites in AM by providing valuable insights regarding their FGF along with areas for improvement.