Reactive
molecular dynamics was used to investigate the atomic-level
mechanism of formic acid-accelerated deterioration of meta-aramid
(PMIA) fibers. The simulation results showed that formic acid promoted
PMIA decomposition. The activation energy of a composite system (PF)
consisting of formic acid and PMIA was 106.94 kJ/mol at 2000–3000
K, which is 11.95% lower than that of pure PMIA. The main small-molecule
products of the PF system were H/C/O-containing molecules (H2O, CO, and CO2), hydrocarbon molecules (e.g., CH4, •C2H, C2H4,
and C3H4), N-containing molecules (N2, NH3, and HCN), H2, and various free radicals.
Formic acid can promote the production of small molecules such as
CO, CO2, and H2O. The N–H bonds, C–N
bonds and the amide CO double bond of PMIA were vulnerable
to CO, H ions, and free radicals produced by formic acid decomposition,
and this decreased the PMIA stability. Temperature is an important
factor in the thermal decomposition of PMIA and can accelerate reactions
in the PF system. The initial reaction rate of PMIA at 3000 K was
8.1 times that at 2000 K, and the intermediate reaction rate was 6.2
times that at 2200 K; temperature also affects the types of pyrolysis
products, for example, hydrocarbons are high-temperature products.