Investigating the pyrolysis mechanisms of three archetypal ablative resins through pyrolysis experiments and ReaxFF MD simulations

Boron (B-PF), high carbon (HC-PF), and silicone phenolic resins (Si-PF) are typical structures of high-temperature resistant resins with exceptional ablation resistance. Nevertheless, the mechanism of their pyrolytic behavior under ultra-high temperatures remains unclear. Herein, the pyrolysis processes and mechanisms of the three resins are investigated in-depth through experiments and ReaxFF molecular dynamics simulations. According to the experimental results, the final residual carbon rate of the resin shows B-PF > HC-PF > Si-PF. The main products of resin pyrolysis are H2, CH4, CO, small molecular hydrocarbons, and phenolic compounds. The simulation results show that the different types of phenolic resins have consistent pyrolysis products. The main small molecule products are H2, H2O, CO and C2H2. Moreover, these reaction paths are monitored and analyzed. The hydroxyl groups on the naphthalene ring in the high-carbon phenolic make the ring more active and susceptible to decarbonization processes, releasing more carbon monoxide (CO). When silicone resins undergo pyrolysis at high temperatures, the resulting H2O reacts with fragments of silicon-containing molecules to form new silicon oxides upon cooling. The B-O bond in boron phenolic undergoes reorganization upon breakage to form a B-containing five-membered ring, a factor that affects its thermal stability. This research reveals the pyrolytic properties of various phenolic resins and provides a theoretical basis for further research into the pyrolytic behavior of different resins.