Isoconversional kinetics of degradation of polyvinylpyrrolidone used as a matrix for ammonium nitrate stabilization

Thermogravimetric analyzer (TGA) has been applied to measure the kinetics of the thermal degradation of virgin polyvinyl pyrrolidone (PVP) and a phase stabilized PVP-ammonium nitrate (AN) material. The PVP-AN samples have been prepared by using 20 wt.% of AN and PVP of three different molecular weights. Virgin PVP undergoes a major mass loss in the region 380-550 degrees C leaving a small amount of nonvolatile residue. The application of an advanced isoconversional method to the respective degradation process demonstrates that its effective activation energy increases from similar to 70 kJ mol(-1) to a plateau value at 250-300 kJ mol(-1), which is independent of the molecular weight. The PVP-AN materials lose spontaneously similar to 20% of their mass on heating above the glass transition temperature of the PVP matrix (160-180 degrees C). After the escape of AN, the remaining PVP matrix degrades in the same temperature region as virgin PVR however, the effective activation energy of this degradation is similar to 150-200 kJ mol(-1). (c) 2008 Elsevier B.V. All rights reserved.