Electrical and mechanical properties of melamine-formaldehyde-based laminates with shungite filler

Abstract

Processing issues and the electrical and mechanical properties of a novel combination of a natural carbonaceous filler, Karelian shungite, and a water soluble thermosetting polymer, melamine-formaldehyde, were investigated. Two types of shungite with different carbon contents were investigated and compared to a commercial carbon black. The larger particle size and chemically more active surface of the shungites compared to carbon black leads to easy handling with little dusting and allows water to be used as dispersant. Laminates of melamine-formaldehyde reinforced with random cellulose fibers and filler were prepared by film stacking. The layered structure results in anisotropic resistivities for the shungites with fairly low in-plane percolation thresholds and a dissipative resistivity above the percolation transition. In comparison, carbon black had a lower percolation threshold and a low isotropic resistivity above the percolation transition. The mechanical properties of the composites were slightly deteriorated by all three fillers, indicating poor interfacial adhesion. The results of Fourier transform infrared (FTIR) measurements are interpreted as indicating hydrogen bonding and thus relatively weak adhesion between filler and polymer. Aqueous mixtures of melamine-formaldehyde and shungite filler had lower viscosities than corresponding melamine-formaldehyde and carbon black filler mixtures.