Rheology and 3D Printability of Percolated Graphene–Polyamide-6 Composites

Graphene–polyamide-6 (PA6) composites with up to 17.0% w/w graphene content were prepared via melt mixing. Oscillatory rheometry revealed that the dynamic viscoelastic properties of PA6 decreased with the addition of 0.1% w/w graphene but increased when the graphene content was increased to 6.0% w/w and higher. Further analysis indicated that the rheological percolation threshold was between 6.0 and 10.0% w/w graphene. The Carreau–Yasuda model was used to describe the complex viscosity of the materials. Capillary rheometry was applied to assess the steady shear rheology of neat PA6 and the 17.0% w/w graphene–PA6 composite. High material viscosity at low shear rates coupled with intense shear-thinning in the composite highlighted the importance of selecting the appropriate rheological characterisation methods, shear rates and rheological models when assessing the 3D printability of percolated graphene–polymer composites for material extrusion(ME). A method to predict the printability of an ME filament feedstock, based on fundamentalequations describing material flow through the printer nozzle, in the form of a printing envelope,was developed and verified experimentally. It was found that designing filaments with steady shear viscosities of approximately 15% of the maximum printable viscosity for the desired printing conditions will be advantageous for easy ME processing.