PREDICTION OF CELLULOSE DECOMPOSITION RATES FROM THERMOGRAVIMETRIC DATA

Thermogravimetric (TG) data is useful for determining the decomposition temperatures and rates of solid materials. Reaction rate parameters such as activation energy (E) and pre-exponential factor (A) can be determined from constant heating rate data using a simplified Arrhenius equation. Unfortunately, there is a wide variation in these parameters, reported in the literature for each substance, depending on the heating rate used among other factors. As a result there is no agreement on the data to be used in extrapolation to other conditions. We have measured the decomposition of cellulose at various heating rates and found that the present form of rate equation explains data only at a single heating rate at which the parameters have been determined. These parameters fail to explain the decomposition data obtained at other heating rates. In this paper we propose an equation of the form: dX/dT = A(o)/a(2) (a(1)/a(2))(m) exp(-E(o)/RT) f(X)(n), where A(o) and E(o) are temperature independent rate parameters, a(1) is the heating rate at which the kinetic parameters A(o) and E(o) have been calculated, a(2) is any other heating rate for which the prediction is to be made, and m is an exponent. This equation is consistent with the original Arrhenius equation and is able to explain the TG data over a wide range of heating rates.