A simultaneous TG-DTA study of the degradation in nitrogen of cellulose to carbon, alone and in the presence of other pharmaceutical excipients

Abstract

The heat treatment of an α-cellulose and a microcrystalline cellulose (Avicel ®) in nitrogen gives a one-stage degradation to carbon. This degradation suffers a temperature transposition in the presence of pharmaceutical excipients, namely dibasic calcium phosphate, stearic acid, magnesium stearate, and silicon dioxide. It is possible to produce a kinetic evaluation of these thermal analysis studies in terms of a comparative method by constructing the theoretical TG trace of the binary mixture based on a presumed no-interaction between the two components. There is a variation in behavior to be noted in the different forms of cellulose, and also different values are shown for the Arrhenius parameters. Such variations are also noted in the Avicel ® degradation in the presence of other materials. These observations should be of use in the characterization of pharmaceutical excipients. The Arrhenius parameters for α-cellulose degradation using D3 (three-dimensional diffusion) mechanism at the temperature range from 580 to 630 K are 289.32 kJ mol −1 and 1.85×10 23 for E act and A, respectively. The Arrhenius parameters for Avicel ® degradation using F1 (first-order) mechanism at the temperature range from 562 to 604 K are 291.35 kJ mol −1 and 1.26×10 25 for E act and A, respectively.