Electrical conductivity of urea–formaldehyde–cellulose composites loaded with copper

Abstract

This work is concerned with the preparation and characterization of composite materials prepared by compression molding of mixtures of copper powder and a commercial grade thermosetting resin of urea-formaldehyde filled with a-cellulose in powder form. The electrical conductivity of the composites is <10 212 S/cm, unless the metal content reaches the percolation threshold of 24.0 vol %, beyond which the conductivity increases markedly by as much as 11 orders of magnitude, indicating an insulator-conductor phase transition. The homogeneity of these composites was checked by the morphologies of the constituents (filler and matrix) and the composites characterized by optical microscopy. The density of the composites was measured and compared with values calculated assuming different void levels within the samples to discuss the porosity effect. Finally, the obtained results on electrical conductivity have been well interpreted with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, V f *, the critical exponent, t, and the packing density coefficient, F, were in good accord with earlier studies. In addition, the hardness of samples remained almost constant with the increase of metal concentration. POLYM. COMPOS., 32:193-198, 2011. ª

Comparison of properties of silver-metal oxide electrical contact materials

“…Density of the obtained samples was determined by standard methods. Applying the procedure given in more detail in [13] theoretical density of samples was calculated and by comparison between experimental and theoretical densities the porosity of samples was determined.…”

“…Theoretical density of composites, ρ t , was calculated according to relation [13][14][15]: (1) where V is volume fraction, ρ -density while f and m indexes correspond to filler (metal oxide powder) and matrix (silver powder), respectively.…”

New Technology for the Synthesis of New Materials Based on Cellulose and Sorption of Noble Metals

“…Owing to their resistance to digestion, they are eligible as potential excipients that could be used in the pharmaceutical industry. Information about numerous existing possibilities of polymers containing dispersed conductive fillers and various methods of manufacture of such materials have been reported widely in the literature (Pinto et al, 2011). Also they found numerous technological applications as self regulating heater, photothermal optical recording, direction finding antennas, chemical detecting sensors used in electronic noses, chemical and electrochemical catalysts and adsorbents .…”

“…As the volume fraction of the conducting filler particles increases, the particles come into contact with one another to form the conduction paths through the composite. As the result there is a critical composition (percolation threshold) at which the conductivity increases by some orders of magnitude from the insulating range to values in the semiconductive or metallic range (Pinto et al, 2011). The conductivity of filled polymers is strongly dependent on the nature of the contact between the conductive filler elements.…”

Recent Progress in Kinetics of Thermal Degradation Mechanisms in Polymer Composites

“…They may either be insulating or conducting, though both of them are equally useful. Insulating composites are applicable as thermal greases, thermal interface materials, and electric cable insulations, while conductive composites are exploited in thermo electrical and thermo mechanical applications, and organic electronics [1,[2][3][4][5][6]. However, in order to continue satisfying the global demands (particularly of energy), there are certain issues which need to be addressed regarding the polymer composites [7].…”