A comprehensive study of pyrolysis characteristics of silicone-modified phenolic aerogel matrix Nanocomposites: Kinetic Analysis, ReaxFF MD Simulations, and ANN prediction

The pyrolysis characteristics of the polymeric nanocomposites are dominantly regulated by the pyrolyzable components to accommodate a specific thermodynamic environment. The pyrolysis mechanisms of the pyrolyzable system including silicone and phenolic aerogels (SiOC/PR) of silicone-modified phenolic aerogel matrix nanocomposites are carried out by kinetic analysis, ReaxFF molecular dynamics (MD) simulations, and artificial neural network (ANN). The experimental results show that the SiOC/PR systems exhibit better thermal stability when the mass ratio of SiOC to PR is 1:3. A distributed activation energy model with five pseudo-components is employed to calculate the kinetic parameters of each decomposition stage of SiOC/PR systems for describing the decomposition characteristics. The significant pyrolysis products detected by TG-FTIR are examined by ReaxFF MD simulations. MD results reveal that the methanol evolution of SiOC/PR systems is distinct in a high-temperature oxygen-free environment, where a mass ratio 1:3 of SiOC to PR is more likely to release methanol and forms a silicon oxide-rich phase with high bond energy. Two reaction mechanisms for methanol identified by the MD trajectory are the extraction reactions of methyl intermediates as well as hydroxymethyl intermediates. The mixture ratio of the pyrolyzable system of the SiOC/PR nanocomposites with optimal thermal resistance equaling 0.22 is predicted by ANN. This work can help understand the system’s chemical features and guide the pyrolyzable system design of the SiOC/PR nanocomposites.