From Reinforcement to Printability: Integrated Structure–Property–Processability Correlations in Hybrid CNT–GO-Reinforced Polypropylene Nanocomposites for Material Extrusion Additive Manufacturing

Abstract

Polypropylene (PP) is a promising feedstock for extrusion-based additive manufacturing due to its low density and chemical resistance; however, its semicrystalline nature induces shrinkage and warpage during printing. This study investigates how hybrid carbon nanotube (CNT)–graphene oxide (GO) architectures influence the mechanical, thermal, melt flow, and dimensional behavior of PP during material extrusion (MEX) and fused granule fabrication (FGF). Neat PP, single-filler controls, and hybrid CNT–GO formulations (total filler ≤ 2 wt.%) were prepared via solvent-assisted dispersion and characterized by tensile/flexural testing, thermal analysis, spectroscopy, microscopy, melt flow index, and warpage measurements. CNT–GO incorporation increased tensile and flexural modulus and strength by up to 55%/57% and 71%/71%, respectively, while reducing ductility. Thermal stability and crystallinity improved, consistent with heterogeneous nucleation. Network development reduced melt flow index, increased apparent flow activation energy, and reduced warpage by up to 58% for the balanced 1:1 CNT: GO formulation. These formulation-dependent trends establish a common material-level link between reinforcement and printability. MEX and FGF showed broadly similar performance under the investigated conditions, with no statistically significant route effect detected for most properties; the balanced hybrid formulation provided the best overall balance between mechanical properties and dimensional stability.