Study on the properties of polypropylene (PP) - exfoliated graphite composites.
Part I. The effect of cluster formation by composite components on the electrical properties of the composite
Polimery 1997, No 4, 244
Volume resistivity (ρ) of PP—exfoliated graphite (EG) composites has been studied over the entire range of EG volume fractions (Θ = 0—1 ) in relation to composite's structure as examined by optical microscopy. The shear stresses arising on mixing of (in a paddle mixer or in a disk-andscrew extruder), and affecting the formation of clusters by, the composite components have been discussed at length. The resulting structure was found to control the ρ vs. Θ and ρ vs.T (temperature) relationships. Three ρ vs. Θ regions were found to occur, separated by the percolation thresholds at Θc = 0.02 and Θc' = 0.047. At Θc = 0.02, the exfoliated graphite particles formed a continuous cluster extending across the entire composite; at Θc' = 0.047, the continuous cluster composed of PP molecules vanished. Within the Θ = 0.02—0.047 and Θ = 0.047—1 intervals, the composite's volume resistivity was found to be related to the resistance of contacts between the exfoliated graphite particles and to the volume resistivity of the exfoliated graphite phase, respectively. Exponential functions taken from the percolation theory were used to describe the ρ=f(Θ) function in each region.