Kinetics of thermal decomposition of unsaturated polyester resins with reduced flammability

In this article, the kinetics of thermal decomposition of unsaturated maleic-phthalic polyester resins, flame-retarded with zinc hydroxystannate, was studied by thermogravimetric analysis at different heating rates. At the first stage, it was found, on the basis of isoconversional analysis by the methods of Friedman and of Ozawa-FlynnWall, that the value of the (apparent) activation energy (E) characteristically changes in three steps during the degradation. Further kinetic studies using nonlinear regression methods revealed the best fits for both pristine and stabilized resins. It was observed that the course of E versus the degree of conversion (alpha) during degradation of zinc hydroxystannate-containing resins (alpha > 0.8) was characterized by higher values of E-this phenomenon can be explained in terms of the flame-retardation action of zinc hydroxystannate, which is believed to operate primarily in the condensed phase. At the next stage, kinetic analysis by the nonregression method was performed to find the kinetic model [f(alpha) function] of the decomposition process; hence, for pristine resin, the best fit was found for the Avrami-Yerofeeyev model (nuclei growth), and for stabilized samples, the nth-order function with catalysis proved to be the best approximation. The obtained kinetic parameters in the form of E, the preexponential factor A, and the model function f(alpha) allow a prediction of the polyester resin's thermal behavior in an extrapolated range of degree of conversion, time, and temperature. (C) 2003 Wiley Periodicals, Inc.