INVESTIGATION OF PYROLYSIS CHARACTERISTICS OF SILICONE-PHENOLIC MATRIX NANOCOMPOSITES THROUGH KINETIC ANALYSIS AND REAXFF MD SIMULATIONS

The pyrolysis characteristics of the polymeric nanocomposites are dominantly governed by the pyrolyzable components to accommodate a specific thermodynamic environment. The pyrolysis behaviour of the pyrolyzable system including silicone and phenolic aerogels (SiOC/PR) of silicone-modified phenolic aerogel matrix nanocomposites was investigated by TG and TG-FTIR, which shows that a mass ratio of PR to SiOC of 3:1 exhibits better thermal stability. The distributed activation energy model (DAEM) was employed to investigate the decomposition kinetics, and the results show that the five-pseudo-components DAEM effectively represents the decomposition conversion signature of SiOC/PR. Methanol, the major volatile product affecting the thermal decomposition of the SiOC/PR system, was analysed at an atomic scale by ReaxFF molecular dynamics (MD) simulations for its reaction pathways. The MD results show that there are two main pathways for the production of methanol, which are extraction reactions of methyl intermediates and hydroxymethyl intermediates, respectively. The Si-O-Si backbone of SiOC can bridge the PR fragments at elevated temperatures, which impacts the yield of condensed residues. Based on TG experimental data, the dependence of weight loss on temperature for SiOC/PR systems with different mixture ratios was predicted by artificial neural networks (ANN). The ANN with a 20*3*1 topology exhibits promising prediction performance. Our work aims to provide practical guidance for engineers to optimize process procedures with a better knowledge of the features of chemical systems.