Kinetics of Polymer Pyrolysis from Surface Regression Rates

Abstract

A method of calculating polymer pyrolysis kinetic parameters from surface-regression-rate data and temperature-profile measurements has been presented. This method is based on the assumption that bond rupture, rather than evaporation and/or diffusion of the monomer, is the rate-limiting step. To apply this method it is first necessary to determine the temperature profile, then the rate is calculated as a sum of the rates of a series of thin isothermal slabs, each at the appropriate temperature along the profile. Because the slope of the temperature profile increases as the regression rate increases, the reaction-zone thickness decreases correspondingly. Thus, the size of the reaction zone is inversely proportional to the rate. This characteristic leads to activation energies about double those obtained by conventional calculations. The results of several sample calculations are tabulated. In addition, certain weaknesses in the desorption-rate-limited mechanism previously proposed are pointed out.