Regulated the orientation of graphene nanoplatelets via flow field in material extrusion for enhancing thermal conductivity

Abstract

Developing polymer composites with high thermal conductivity while maintaining low filler content remains a challenge. The aim of this study is to arrange graphene nano-platelets (GNP) into highly aligned structure within polypropylene (PP) matrix by utilizing the flow field during the material extrusion (MatEx) additive manufacturing process. Finite element simulation was employed to clarify the flow field distribution under varying nozzle diameters and printing speeds. The dispersion and orientation of GNP were systematically characterized, and the microstructure of the printed composites was further correlated with their thermal conductivity. It was found that the orientation degree of GNP is strongly dependent on the intensity of flow field during the MatEx process. By reducing nozzle diameter from 0.6 mm to 0.3 mm and increasing printing speed from 200 mm/min to 600 mm/min, the Hermans orientation factor f of GNP increases from 0.28 at 0.6 mm nozzle and 200 mm/min to 0.74 at 0.3 mm nozzle and 600 mm/min. This enhancement facilitates the formation of efficient and ordered thermally conductive pathways along the through-plane direction. Moreover, the through-plane thermal boundary resistance is also notably improved, decreasing from 7.25 × 10⁻⁵ to 1.17 × 10⁻⁵ m²K/W. The aligned microstructure of the composites, printed using a 0.3 mm nozzle at a 600 mm/min printing speed, yields a superior thermal conductivity of 2.18 W/m·K with only 1.23 vol% GNP, indicating an impressive enhancement efficiency of 690 %. Coupled with the capability of MatEx to construct complex structures and shapes, this strategy holds great promise for achieving efficient heat dissipation devices with low filler loading.