Under oxidative environment the thermal degradation of lignocellulosic materials like wood or pulp is
sensitive to slight composition changes. For this, in order to complement the chemical and X-ray diffraction
results, thermogravimetric analyses (TGA) were used to monitor pulp production in a modern pulp
mill. Runs were carried out on crude, oxygen delignified and bleached pulps from three eucalyptus woods
from different species and geographical origins. Moreover, with the modeling of thermogravimetric data,
it was possible to obtain an approximate composition of samples which includes crystalline and amorphous
cellulose. TGA results show that pulping has an intensive effect on bulk lignin and hemicellulose,
but it has limited influence on the removal of these substances when they are linked to cellulose microfibril.
The stages of oxygen delignification and bleaching, based in chlorine dioxide and hydrogen peroxide,
increase the crystalline cellulose volatilization rate. These changes are compatible with a more crystalline
microfibril. The influence of the fibre size on pulp composition, crystallinity and thermal degradation
behavior was observed.