Effects of the total content of eutectic Sn-Cu alloy and Cu particles used as conductive filler on the structure and properties of polyamide-66 composites

Incorporating both a low-melting-point metal (LMPM) and a high-melting-point metal (HMPM) into a polymer is a promising approach to prepare highly conductive, melt-processable composites. The effects of the total content of the two metals on the structure and properties of the composites were studied in this work through a eutectic Sn-Cu alloy/Cu particles/polyamide-66 ternary system. The structure, conductivity, fluidity and toughness of the composites were characterized by scanning electron microscopy, four-point probe or two-electrode method, small amplitude oscillatory shear testing and Charpy impact testing, respectively. The results show that the morphology of metal phase in the composites transforms from isolated “islands” to a physically continuous network as the total metal content increases. The percolation threshold for the composites is lower than that of traditional metal-filled polymer composites. The complex viscosity and impact strength of the composites vary non-monotonically with the total metal content and exhibit a minimum. The enhancement in the conductivity and toughness of the composites is related to the formation of the physically continuous conductive network. Overall, the filler content dependences of the structure and properties of the LMPM/HMPM/polymer composites are different from those of traditional conductive polymer composites. The combination of LMPM and HMPM helps reduce the filler content and mitigate the composite fluidity deterioration.