Correlation between percolation behavior of electricity and viscoelasticity for graphite filled high density polyethylene

A study on the correlation between electrical percolation and viscoelastic percolation for graphite (GP) filled high-density polyethylene (HDPE) conductive composites was carried out through an examination of the filler concentration φ dependence of the volume resistivity ρ and dynamic viscoelastic functions. The frequency ω dependence of G′ at low ωs decreased obviously with increasing GP concentration. The relationship between φ and the proportion of dynamic storage modulus of the composites to that of the polymer matrix, namely the relative dynamic storage modulus (Gc′/Gp′), at low frequency region was studied. It is found that there are two critical threshold, φr1 and φr2, in plots of φ∼Gc′/Gp′, which is close to the electrical percolation threshold φ1 and φ2, respectively. Moreover, there exists φ-dependence of the dynamic loss tangent (tan δ) and a peak in plot of tan δ versus ω when φ approaches the loss angle threshold, φδ1 (8 vol%). When φ>20%, the second loss angle threshold, φδ2, the tan δ shows almost no dependence on the GP content. φδ1 and φδ2 is close to the electrical percolation threshold. A modified Kerner-Nielson equation was also obtained and used to analyze the formation of network structure in the matrix by substituting variable parameter K for constant A. The results indicate that the parameter K increases discontinuously with increasing φ, revealing this parameter is associated with GP concentration, and the critical threshold φK1 and φK2 is close to the electrical percolation threshold φ1 and φ2, respectively. Furthermore, the viscoelastic percolation for GP/HDPE composites can be verified on the basis of the modified equation.