Variations dimensionnelles accompagnant le traitement thermique de la cellulose sous atmosphàre inerte

Abstract

In this paper, we study the dimensional variations accompanying the thermal decomposition of cellulose, under nitrogen atmosphere, from the ambient temperature to different final temperatures of the reaction. Consequently, two series of tests are achieved. In the first set, the residue of cellulose is cooled, once the desired temperature is reached. In the second set, when the desired temperature is reached, the residue of cellulose is maintained at this temperature for a duration of time varying from zero to two hours. The dimensional variations are measured on cylinders of 3 mm in diameter and 9 mm in height, prepared from the cellulose powder. The cellulose residues are then analysed using scanning electron microscopy. The results show that the dimensions of cellulose cylinders change in the longitudinal as well as in the transversal direction. Furthermore, the dimensional variations of the first set of these tests reveal the ranges where the cellulose contracts and then dilates. The results of the second set indicate that, when the residue is maintained two hours at the final temperature of reaction, the evolution observed in the first series of tests is hidden. The difference observed in the results of the two series of tests can be explained by the measurements performed, as a function of time, at 300°C and 380°C. These measurements show the influence of residue residence time on the dimensional variations of cellulose. A physical explanation of the exothermic effect accompanying the last stage of cellulose pyrolysis can be provided on basis of the concept of the fracture mechanics, with the dimensional variations and fractographics taken by scanning electron microscopy.