Non‐linear electrical conductivity of urea‐formaldehyde‐cellulose loaded with powders of different carbon fillers

Abstract

This article reports on the making and characterization of composite materials prepared by compression molding of a commercial grade thermosetting resin of urea-formaldehyde filled with ␣-cellulose in powder form mixed successively with carbon black, synthetic graphite, and activated carbon. The morphology of the constituents and the composites has been characterized by optical microscopy. The porosity effect has been discussed from density measurements. Furthermore, it has been shown that the hardness of the samples remains almost constant with the increase of filler concentration. The electrical conductivity shows clearly a non-linear behavior. The observed values are lower than 10 Ϫ11 S/cm, unless the filler content reaches the percolation threshold beyond which the conductivity increases markedly by as much as ten orders of magnitude, indicating insulator-conductor phase transition. The conduction threshold depends on the filler nature. The results have been interpreted by means of the statistical percolation theory.

Electrically conductive composites of poly(urea‐formaldehyde) and cellulose filled with aluminum

“…It behaves linearly when the amount of metallic filler increases, like binary compound. This indicates that the obtained composites are homogenous, in good accord with previous studies using the same matrix [18–20] and microscopic observations. The theoretical density of the composites was calculated with binary Eq.…”

“…The hardness of samples remains approximately constant, as 85 ± 5 Shore D values, independently of the filler composition, as found for other composites prepared with the same matrix [18–20, 22].…”

“…Before starting a new test, the electrodes were short‐circuited for 5 min to eliminate any effect of the previous electrification. The procedure used in the present study to estimate the electrical conductivity, σ, from electrical resistance, in the present study was similar to that reported earlier [18, 19].…”

“…This work deals with further developments in previous reported investigations of preparation and characterization of different electroconductive (thermoplastics and thermosets) polymer composites [1, 15–22]. We report an experimental study about the influence of filler concentration on the electrical conductivity of composites elaborated by hot compacting, i.e.…”

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

“…This article deals with further developments in previous reported investigations of preparation and characterization of electroconductive polymer composites [21–29]. We report an experimental study about the influence of filler concentration on the electrical conductivity of composites elaborated by hot compacting, i.e.…”