(321b) Lightweight Composites: Effect of Shear and Filler Concentration on Alignment, Thermal Conductivity, and Mechanical Properties of Functional Ink

Over the past decade, there has been significant interest in the additive manufacturing (AM) of thermosetting resin composites. However, there are issues associated with functionality of the composite, toughness, conductivity, and mechanical properties of the printed structure due to its standard processing techniques. Extrusion-based AM can be used to produce thermoset resin-filler composites with enhanced thermal properties and toughness at loading levels well above the percolation threshold. By optimizing the printing parameters via direct ink writing, lightweight composite materials can be engineered with enhanced properties, so they can be used in applications such as electromagnetic shielding materials, heat sinks, and thermal interface materials because they enhance the thermal coupling between two materials.¹

In this work, EPON 862 resin was mixed at varied weight concentrations (10%, 11%, 13%, 15%, 16%, 17%, and 18%) of reduced graphene oxide (RGO) fillers to investigate how the macroscopic properties of printed RGO composites are affected at the different weight concentrations, and print speeds (10mm/s and 40mm/s). The rheology of each sample was tested to see the effect of filler concentration on the modulus, viscosity, and yield stress/strain of the samples. The thermal diffusivities and mechanical properties were measured through LFA (Laser Flash Analysis) and DMA (Dynamic Mechanical Analysis) techniques.

The thermal diffusivity of the 13wt% samples printed at 10mm/s were ~0.80 mm2/s at room temperature and 0.66 mm2/s at 100C. When printed at 40mm/s, they were 0.87 mm2/s at room temperature and 0.70 mm2/s at 100C. For the samples at 18wt% printed at 10mm/s, the thermal diffusivities were ~1.09 mm2/s at room temperature and 0.89 mm2/s at 100C and, and when printed at 40mm/s, the thermal diffusivity was 1.22 mm2/s at room temperature and 1.01 mm2/s at 100C. These results indicate as print speed increases, the thermal diffusivity and conductivity increases. This increase can be attributed to the shear-induced alignment of the particles that are extruded on the printing substrate. DMA analyses also showed an increase in Tg (glass transition temperature) at 40mm/s compared to 10mm/s print speed, due to the alignment of the filler particles reinforcing the strength of the material by restricting the polymer chains at higher temperatures. Further experiments are being done to measure the mechanical properties of the samples and investigate the effect of shear on the tensile strength of the composite.

¹Haney, R. et al. Printability and Performance of 3D Conductive Graphite Structures. Additive Manufacturing 2021.