Structure-dependent conductivity and microhardness of metal-filled PVC composites

• Published in: Macromolecular symposia. 2001-05, Vol.169 (1), p.297-306
• Main Authors: Mamunya, Yevgen P., Privalko, Eleonora G., Lebedev, Eugene V., Privalko, Valery P., Calleja, Francisco J. Balta, Pissis, Policarpos
• Format: Article
• Language: English
• Subjects: Composition effects; Copper; Fillers; Microhardness; Nickel; Particle size; Particulate composites; Polyvinyl chlorides
• ISSN: 1022-1360; 1521-3900
• DOI: 10.1002/1521-3900(200105)169:1<297::AID-MASY297>3.0.CO;2-Z

Metal‐filled composites of a commercial PVC (polyvinyl chloride) powder (mean particle size dp ≈ 100 microns) and a metal powder (mean particle size df about 100 microns for copper, Cu, and about 10 microns for nickel, Ni) prepared by mechanical mixing in a ball mill, subsequent hot‐pressing at 443 K and rapid cooling to 300 K, were characterized by the room‐temperature measurements of electrical conductivity σ, density ρ and microhardness H. The sudden jumps of about 17 orders of magnitude followed by a much slower growth up to the limiting filler fraction ϕ* on the log σ vs. ϕ plots are the evidence for the onset of percolation transitions, at filler volume contents ϕc1 = 0.05 and 0.04 for PVC/Cu and PVC/Ni, respectively. For both systems, the values of H exhibited an initial steep increase up to ϕc2 = 0.07, followed by an apparent plateau extending up to ϕ = 0.18. However, drastic differences in the patterns of composition dependence of H were observed at higher metal loadings, i.e., a continuous increase of H up to the leveling‐off at ϕ* for PVC/Cu, in contrast to a sudden drop of H at ϕ = 0.20 and subsequent slow increase for PVC/Ni. For both composites the apparent density ρ′ of a polymer matrix remained the same as that of the neat PVC in the composition interval ϕ < 0.20, while at ϕ* > 0.20 a precipitous drop of ρ1 was observed due to the formation of polymer‐free voids between filler particles (crowding effect) as ϕ approaches ϕ*. The observed effects were analyzed in terms of a tentative model envisaging cross‐overs from “dilute suspension regime” to “semi‐dilute suspension regime” in the concentration range ϕc1 to ϕc2, and from “semi‐dilute suspension regime” to “concentrated suspension regime” above ϕ = 0.20. Different behavior in this latter regime was explained by intrinsic differences in the structure of conductive infinite clusters between mixtures of particles of about the same size (PVC/Cu) and of widely different sizes (PVC/Ni).