Population-based models of thermoplastic degradation: Using optimization to determine model parameters

A comparison of different model forms for non-oxidative thermoplastic degradation rate is presented. A physically meaningful model is derived from a three-step radical depolymerization mechanism. A moment-based approximation to the population balance equations is derived and implemented to predict the thermal degradation of polyethylene (PE) and poly(methyl methacrylate) (PMMA). In the absence of accurate molecular dynamical calculations to predict the controlling model parameters, it is necessary to use experimental data to find the best fit parameter values. A sequential quadratic programming algorithm (SQP) was used to find the set of parameters that minimized the error between the model and sets of non-isothermal thermogravimetric (TG) data at different heating rates for PE and PMMA.