Highly thermally conductive polyamide 6 composites with favorable mechanical properties, processability and low water absorption using a hybrid filling of short carbon fiber, flake graphite and expanded graphite

It is a challenge to maintain the mechanical properties and processability of thermally conductive polymer composites in the presence of high filling of heat conductive filler. An optimized hybrid filler system composed of flake graphite (FG), expanded graphite (EG) and short carbon fiber (CF) was introduced into PA6 matrix. The addition of EG to PA6 was found to be more effective in improving its thermal conductivity, while the addition of FG maintained favorable processability due to its lubrication effect. Furthermore, the hybrid filling of FG and EG has a synergistic effect on the enhancement of thermal conductivity. The ternary filling of FG, EG and CF produced highly heat conductive PA6 composites with high strength, favorable processability, and low water absorption. The thermal conductivity of 10CF/20FG/10EG/PA6 composite reached 3.45 W/m k, which is 12.3 times of pure PA6. Additionally, the flexural strength increased to 110 MPa, which is 37 % higher than that of pure PA6, and the water absorption was reduced to one quarter that of pure PA6.