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This article presents an investigation into the influence of carbon nanotube (CNT) loading on electrical properties, rheology, printability, and mechanical properties of polyetherimide- Short carbon fiber (PEI-SCF) composites for large area additive manufacturing (LAAM). Two PEI-SCF composites with similar carbon fiber (SCF) content and different CNT loadings, labeled PEI1 (lower CNT loading) and PEI2 (higher CNT loading, twice that of PEI1), were analyzed. During compounding, it was observed that the higher CNT content led to increased viscosity and porosity in the extruded pellets. When these pellets were used for the injection molding process, both PEI1 and PEI2 yielded samples with similar mechanical properties due to consistent injection pressure. However, after LAAM, PEI1 retained the injection molding strength better than PEI2 due to lower overall porosity and superior print quality. Density measurements showed a direct correlation with strength in the X plane, where lower-density samples had lower strength and higher void content. In contrast, the void location and interface healing were the primary factors driving the Z strength. The results highlight the significance of CNT content in managing rheology, printability, and print quality, thereby improving the mechanical properties of PEI-SCF composites produced via LAAM. Lower temperatures and extended layer times improved print quality and reduced porosity for both formulations, though they impacted the Z-axis strength. Overall, PEI1 with lower CNT content demonstrated better printability and mechanical properties compared to PEI2 with higher CNT content. Further, the addition of CNTs resulted in a significant reduction in both surface and volume resistivity compared to PEI reinforced solely with carbon fibers.
Kadiyala et al. (Sun,) studied this question.