Degradation of polycaprolactone in supercritical fluids

The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 degrees C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 degrees C and 50 bar. The effect of pressure on degradation was also evaluated at 325 degrees C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250-300 degrees C) and by chain end scission (325-375 degrees C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 degrees C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2-24 degrees C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature. (C) 2008 Elsevier Ltd. All rights reserved.