TYPICAL SOURCES OF ERROR IN THE KINETIC-ANALYSIS OF MODELS WITH PRE-EQUILIBRIA - DSC INVESTIGATIONS OF EPOXIDE-AMINE CURING REACTIONS

Reversible steps are included in many reaction models. If the intermed iate reaches an equilibrium with the reactants, the kinetic evaluation may be simplified by using the corresponding equilibrium constant. Th en, the adequate modelling of the reaction is based on the equilibrium concentrations of all participants of such a pre-equilibrium. Using D SC data for the investigation of kinetic problems, the concentrations are frequently replaced by the degrees of conversion (reaction). The f ormal use of degrees of conversion instead of concentrations results i n incorrect kinetic equations. A typical example is the overall equati on for the description of the epoxide-amine curing reaction. Another s erious source of error is the unknown degree of conversion together wi th the unknown heat-flow rate at the apparent ending of the reaction. The resulting difficulties can partially be overcome, if the parameter s of the complete set of differential equations are determined by mult ivariate nonlinear regression. (C) 1997 Elsevier Science B.V.