Improving Heat Transfer in Fused Deposition Modeling with Graphene Enhances Inter Filament Bonding

Fused deposition modeling (FDM) serves as a promising manufacturing technique that can efficiently build complex structures and complicated designs. However, the printed prototypes using FDM lack isotropic and robust mechanical properties required for large scale manufacturing. In this study, we seek to develop new polymeric materials for improved FDM processing by examining the use of graphene as a filler for PLA to enhance thermal conductivity, and correlate these changes to its impact on thermal evolution during printing, inter-filament voids, and mechanical properties of the fabricated samples. These results show that the addition of graphene to PLA filament improves inter-filament bonding because of improved thermal conductivity, where the improved thermal transport translates to longer times at elevated temperatures. This results in more inter-filament diffusion of the polymers that manifests as stronger filament-filament interfaces, more robust and isotropic samples and fewer inter-filament voids. However, the improvement only occurs at lower graphene loadings (∼0.5%) because at higher loadings any increase in inter-filament polymer diffusion appears to be slowed by the presence of the graphene sheets – a well-known phenomenon in polymer nanocomposites. Thus, the results presented here indicate that using fillers with high thermal conductivity provides pathways to tailor the thermal transport and profile during printing, effectively controlling heat transfer and offering a rational method to optimize the inter-filament interfaces and structural mechanical properties of printed structures.