DIMENSIONAL VARIATIONS ACCOMPANYING THERM AL-TREATMENT OF CELLULOSE IN AN INERT ATMOSPHERE

In this paper, we study the dimensional variations accompanying the th ermal decomposition of cellulose, under nitrogen atmosphere, from the ambient temperature to different final temperatures of the reaction. C onsequently, two series of tests are achieved. In the first set, the r esidue of cellulose is cooled, once the desired temperature is reached . In the second set, when the desired temperature is reached, the resi due of cellulose is maintained at this temperature for a duration of t ime varying from zero to two hours. The dimensional variations are mea sured on cylinders of 3 mm in diameter and 9 mm in height, prepared fr om the cellulose powder. The cellulose residues are then analysed usin g scanning electron microscopy. The results show that the dimensions o f cellulose cylinders change in the longitudinal as well as in the tra nsversal direction. Furthermore, the dimensional variations of the fir st set of these tests reveal the ranges where the cellulose contracts and then dilates. The results of the second set indicate that, when th e residue is maintained two hours at the final temperature of reaction , the evolution observed in the first series of tests is hidden. The d ifference observed in the results of the two series of tests can be ex plained by the measurements performed, as a function of time, at 300 d egrees C and 380 degrees C. These measurements show the influence of r esidue residence time on the dimensional variations of cellulose. A ph ysical explanation of the exothermic effect accompanying the last stag e of cellulose pyrolysis can be provided on basis of the concept of th e fracture mechanics, with the dimensional variations and fractographi cs taken by scanning electron microscopy. (C) 1997 Published by Elsevi er Science B.V.