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

Abstract

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 fundamental equations 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.

Rheological Investigation of Hydroxypropyl Cellulose–Based Filaments for Material Extrusion 3D Printing

“…This range is broader than previously reported [ 60 ], in particular, the upper limit. The greater complex viscosity could be attributed to the impeded polymer mobility as a consequence of the increased drug–filler–matrix interactions [ 68 ]. The lower viscosity of 45% HPC (F10 and F11) compared to 67.5% HPC (F1 and F2) may be linked to the reduced Tg of the blends (Tg of HPC [ 55 ], SLP [ 69 ] and PVP/VA [ 52 ] = 120, 70 and 104 °C, respectively) and the decreased polymeric chain interaction [ 47 ].…”

“…At 200 °C for FDM printing, the slopes of all formulations ranged from −0.3 to −0.7, which is a broader range than in Ilyes’ work (−0.4 to −0.6) [ 51 ]. Greater shear thinning behavior or a higher slope value could be caused by the predominant interactions between the additive and polymer, and the breakage of the HPC polymer networks at a high frequency [ 68 , 82 ]. The addition of CrosPVP showed the greatest shear-thinning effect among the disintegrants upon printing (200 °C).…”

Emerging Research in Conductive Materials for Fused Filament Fabrication: A Critical Review

“…The rapid increase in viscosity was directly attributed to dominant polymer chain entanglement, which was promoted by the increased filler loading of graphene. [ 71 ] Although high viscosity polymers and composites can be printed in FFF, they require high print temperatures and high torque motors to push the filament through the nozzle. Without optimized parameters, this can result in poor printing quality.…”

Direct Ink Writing of Recycled Composites with Complex Shapes: Process Parameters and Ink Optimization

“…[14,22,23] Others relate the extrusion force produced by an FDM extruder to the rheological properties of a molten polymer. [24,25] The models already available in literature do not consider differences in rheological behavior during the extrusion process of a 3D-printable ink. In a previous work, rGFRP inks showed a Newtonian behavior at lower shear rates and a pseudoplastic behavior at higher shear rates.…”