Viscoelastic and high strain rate response of anisotropic graphene-polymer nanocomposites fabricated with stereolithographic 3D printing

Abstract

The viscoelastic and high strain rate response of stereolithographically 3D printed graphene - PMMA nanocomposites was investigated using dynamic mechanical analysis (DMA) and the Split-Hopkinson pressure bar. The obtained experimental data were compared with the quantitative predictions of a simple viscoelastic micromechanical model. Our results confirmed that property anisotropy of the graphene nanocomposites arose from the alignment of graphene platelets along the printing axis within the polymer matrix. If a load is applied along this axis, the nanocomposite will adopt an isostrain (Voigt) geometry, exhibiting large dynamic modulus and strength values. These properties were found to improve with increasing graphene concentrations, up to 0.05 wt%, and post-print bake temperatures, up to 120 °C. Supporting evidence from differential scanning calorimetry and DMA temperature sweep test indicates that this is due to good interfacial bonding between the graphene and polymer, which allowed for efficient load transfer, and that a post-print heat treatment can increase the degree of cure in the polymer. Similar trends were observed for complex lattices fabricated using the same method. Comparing the dynamic mechanical properties of the graphene nanocomposites against that of other lightweight engineering materials, it was found that the nanocomposites exhibited specific strengths that were higher than most Al alloys and comparable to the best literature values reported for graphene – polymer and carbon nanotube – polymer composites. The additively manufactured graphene nanocomposite lattices also showed better energy absorption capabilities than balsa wood, syntactic ceramic foams and Al foams on a per unit weight basis. These results are remarkable considering that the amount of graphene added (≤ 0.10 wt%) was an order of magnitude lower than that usually employed in other studies.