Reactive molecular dynamics simulations to investigate effects of nanopores on crosslinked phenolic resin pyrolysis

Abstract

Phenolic resins used as ablative materials in thermal protection systems (TPS) for atmospheric entry and as precursors for glassy carbon (GC) products undergo complex structural and chemical transformations during pyrolysis. The development of pores and cracks leads to fracture and fragmentation of the resin structure. Achieving an atomistic understanding of the origin of cracks poses significant challenges for experimental in situ techniques. We employ molecular dynamics simulations using reactive force-field (ReaxFF) models to investigate highly cross-linked phenolic resin structures with predefined nanopores, providing insights into this effect. The byproducts, including char and volatile gases, are characterized in detail. Our findings indicate that pressure within the nanopores increases with both temperature and pore size, correlating with the cracks observed in previous GC experiments. The activation energies for vapor generation, both with and without predefined pores, range from 42.05 ± 2.47 to 48.98 ± 5.99 kcal/mol, aligning closely with existing literature. Notably, we observe that cracks originate from the nanopore sites, providing atomistic evidence that corroborates our prior experimental observations. These insights are relevant to the structural design and engineering of effective materials for TPS, energy, and electronic applications.