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.

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Paz I., Fernández A., Matías C., Pinto G. (2014): Effect of temperature on the evolution of colour during the maceration of fruits in liquor. Czech J. Food Sci., 32: 90-95.The effect of temperature on the kinetics of pigment extraction during the maceration of different fruits (raspberry, blackberry, and cranberry) into a commercially available hard spirit (orujo, with 42% v/v ethanol) was evaluated. The analytical method used was UV-Vis spectrophotometry. The initial extraction rate showed an Arrhenius-type dependence with apparent energy activation of 28.8, 69.8, and 55.6 kJ/mol, respectively. Furthermore, a study about the evolution of the colour (from colourless to reddish colour appearance) during the soaking process was done by calculating the CIE tristimulus values (X, Y, Z) for illuminant C, until reaching the apparent stabilisation of colour, which occurs after about two to four weeks for the studied temperatures (5, 23, and 40°C). Studies about the evolution of colour in the soaking process of this kind of fruit liquors can lead to a better understanding of this process, and thus to a better control over the mechanisms underlying it.