Characterization of dispersion and percolation of filled polymers: Molding time and temperature dependence of percolation time in carbon black filled low density polyethylene

The degree of dispersion of fillers such as carbon black (CB) particles in a polymeric matrix is known to be a determining factor of the physical properties of composites. The dispersion state of particles in the polymeric matrix was found to be affected not only by the volume fraction of particles but also by the preparation conditions of the composite such as press time and temperature. At a given CB volume fraction, we measured the electrical conductivity of the composite films, which were molded at a temperature higher than Tm of polyethylene (LDPE), as a function of press time. As a result of aggregation of CB, the networks-facilitating electrical conduction were formed and percolation-like transition was observed at a characteristic time. We have defined the characteristic time as a percolation time (t P ). It was found that the t P decreased with increasing CB volume fraction and increasing molding temperature. The change of the dispersion state of CB in a polymeric matrix was characterized by a digital image analysis of a photograph by scanning electron microscopy.