Logistic approach to polymer degradation in dynamic TGA

The method presented in this work allows for fitting an overall TGA curve by generalized logistic regression. It is assumed that overlapping processes may be involved in a single step of a TGA trace. Since the logistic functions reproduce very well the typical asymptoticity at the beginning and end of degradation processes, the authors consider that each single degradation process can be fitted by a single logistic function or by the linear combination of a small number of them. Since the fitting is very good, the generalized function can replace the original TGA curve. This way, it is possible to differentiate directly the overall TGA curve fitted, overcoming the problems of noise and over-under smoothing, typical in DTG calculation. On the other hand, the separation of overlapping processes in several functions suggests that each single overlapping degradative process could be explained by one or the linear combination of few logistic functions. Particularly, one of the parameters obtained with this kind of logistic mixture represents the point in the time (or temperature) axis where each process is "centered", while another parameter is related to the degradation rate. (C) 2004 Elsevier Ltd. All rights reserved.