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

Abstract

This article addresses the preparation and characterization of composite materials obtained with compression molding of mixtures of aluminum powder and a commercial grade thermosetting resin of poly(urea‐formaldehyde) filled with α‐cellulose in powder form. The homogeneity of these composites was checked by the morphologies of the constituents (filler and matrix) by optical microscopy. The density of the composites was measured and compared with values calculated by assuming different void levels within the samples, to discuss the porosity effect, in connection with optical microscopy observations. Then, the dependence of electrical conductivity of the composites on volume fraction of the metal filler was investigated. The conductivity of the composites is <10−12 S/cm unless the metal content reaches the percolation threshold at a volume fraction of Vc = 38.6 vol%, beyond which the conductivity increases markedly by as much as nine orders of magnitude, indicating an insulator–conductor phase transition. 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, Vc, 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., 2012. © 2012 Society of Plastics Engineers

Morphology, thermal stability and thermal degradation kinetics of cellulose-modified urea–formaldehyde resin

“…A generalized linear integral isoconversional method has been recently put forward by mathematically treating equation (11), which results in equation (12) [24]:…”

“…It therefore finds numerous industrial applications including decorative laminates, textiles, paper, foundry and moulds, wrinkle-resistant fabrics, cotton blends, wood gluing and electrical appliance casings [3][4][5][6][7]. It is capable of serving as a polymer matrix in UFC/metal composites, which shows interesting electrical/dielectric properties with a number of worldwide applications [8][9][10][11].…”

Thermal degradation of urea‐formaldehyde cellulose composites filled with aluminum particles: Kinetic approach to mechanisms

“…The freshly prepared samples were cooled at room temperature for 30 min. In order to improve the finishing of pellet samples and for obtaining better structural characterization results, the surfaces of the samples were polished with sandpaper …”

“…In order to carry out the morphological analysis of neat UFC and UFC/Al composites, a pre‐dried electrically insulator/conductor pair of composites was selected above and below the electrical percolation threshold (38.6 vol % of aluminum) within the relatively stable conductivity regions and was named UFC/Al5vol % and UFC/Al55vol % respectively.…”

“…UFC thus formed finds industrial applications in textiles, paper, foundry and molds, wood gluing and electrical appliances casings . A fascinating class of materials is developed by loading UFC with metal particles, which is economical, environmentally friendly and multipurpose . Like other polymer/metal composites, UFC/metal composites may either be electrically/thermally insulating or conducting though both of them are equally useful.…”