General treatment of the thermogravimetry of polymers

TLDR

The study develops theoretical equations for polymer decompositions that accommodate non‑simple reaction orders and multi‑reaction systems with differing activation energies. The authors critically review thermogravimetric kinetics literature, unify it into a coherent framework with consistent notation, and introduce a novel programming approach that simplifies the mathematics by treating heating rate as a variable. The work demonstrates that varying order, activation energy, heating rate, and temperature dependence shape thermograms, and introduces improved and new kinetic analysis methods—including variable‑rate and multi‑trace approaches and a rate‑conversion technique—that uniquely determine kinetic parameters.

Abstract

Theoretical equations are developed for typical decompositions of polymers including those in which the volatilization does not follow a simple "reaction order" and those made up of a composite of several reactions of differing energies of activation. The effects of order, activation energy, heating rate and temperature dependence upon the calculated thermograms is illustrated. The literature on thermogravimetric kinetics is critically reviewed and coalesced into a logical and coherent development stressing the interrelation of methods and employing a consistent system of notation. As a result, a number of improved methods and new methods for the analysis of kinetic data applicable to the complex systems mentioned above are developed. It is concluded that methods involving a variable rate of heating or involving several thermogravimetric traces at different rates of heating are capable of establishing the uniqueness of kinetic parameters. A new method of determining initial parameters from rate-conversion data is developed. A novel concept is employed of programming reaction variables (in this case, the heating rate) in a manner which greatly simplifies the mathematics of the kinetic system and which shows promise of a wide range of applicability in the area of rate processes.