Novel Biodegradable Composites Based on Lignocellulose and Electrodeposited Copper Powders

Composite materials nowdays are increasing industrial applications worldwide. Composites based on polymers with conductive fillers are getting wider research focus primarily because of their growing importance from the point of application in: electronics, medicine, industry and so on. Besides mentioned above, these composites have found application as contact conductive materials, electromagnetic and radio wave shields, photothermal optical recorders, electronic noses sensitive to certain chemicals, as well as economically acceptable catalysts. The results of experimental studies of the properties of composite materials based on lignocellulosic (LC) and Poly(methyl methacrylate) (PMMA) matrices filled with electrolytic copper are presented in this chapter. Volume fractions of metal fillers in tested composite materials were varied in the range of 1.6–30% (v/v), and the samples were prepared both by compression – cold pressing and hot moulding. The results have shown that shape and morphology of the copper powder, and filler at all, play a significant role in the phenomenon of electrical conductivity of the prepared samples, as well as on the appearance of percolation threshold. The particles with highly developed free surface areas like dendrites, having highly branched structures (such as electrolitically obtained copper powder particles) can much easier form interparticle contacts at lower filler volume fractions than the particles with more regular surface. Layered electrical conductivity throughout the entire sample volume was observed, whereby the resistance of the inner layers was the leading processes of the entire composite resistance. It can be seen that the resistance has increased due to increased contribution of the polymer matrix inner surface area as the frequency decreased. Conductivity measurements have shown typical S-shaped dependence with the percolation transition from nonconductive to conductive region. For all the processing pressures, the percolation threshold for smaller particle sizes was lower than for larger ones. This difference has increased with the increase of processing pressure. A significant increase in the electrical conductivity have been observed when the content of conductive filler in the composites reached the percolation threshold. The effect of particle packaging and pronounced interparticle contact with smaller, highly porous and dendritic particles with large specific surface areas, led to a “shift” of percolation threshold to lower values of filler volume fractions. It was noticed that this transition occurred at lower values of filler content than it was stated in the literature, which is due to the use of fillers with large specific surface areas.