The pyrolysis behavior of poly(styrene–methyl methacrylate) copolymer and expanded polystyrene (EPS) foams using model-free and model fitting methods

The pyrolysis of lost foam casting (LFC) patterns with the type of St-MMA poly(styrene–methyl methacrylate) copolymer and EPS (expanded polystyrene) was investigated by using the thermogravimetric analysis in the inert nitrogen atmosphere at various linear heating rates. The differential form method, temperature approximation integral form method, and numerical integral method were, respectively, employed to compute the empirical activation energy ( E α ) and a comparison was made between them. We discovered that, numerical integral method not only reveals more details but also does not introduce any extra error. Although the calculated E α of St-MMA is lower than that of EPS, unstable changes occur at the initial stage due to the decomposition of short chain. The reaction mechanism of EPS as the 3/2-dimensional Avrami–Erofeev model can be revealed by z ( α ) master plots of iso-conversional method. However, the St-MMA degradation process cannot be interpreted by a common reaction model but can be explained by the sophisticated mechanism signified by the Sestak–Berggren equation through nonlinear regression optimization which uses model fitting method. The simulated conversion rate equation integrated by Runge–Kutta algorithm was in agreement with experimental results, indicating the possibility to predict the pyrolysis rate during LFC process.