Investigation of polyurethane pyrolysis characteristics using reactive force field molecular dynamics

Polyurethane (PU) pyrolysis characteristics were investigated using reactive force field molecular dynamics simulations to reveal the product distribution and thermal decomposition mechanisms. A PU molecular model was constructed and simulated its pyrolysis process at 1,500-3,000 K, analyzing potential energy changes, product species, carbon-containing component distribution, main gas products, main intermediate products and initial cleavage pathways. At 1,500 K, PU mainly decomposes into NHCOO and CH₂ fragments, with concurrent gas release. At 1,800-2,100 K, aromatic amines, olefins, and gases (including CO₂, CO, and NH₃) are formed through radical recombination. At higher temperatures (2,400-3,000 K), carbon rearrangement is promoted, yielding dense C₄₀ ⁺ species alongside persistent gases. The results show that PU pyrolysis initiates with the C-O-C bond cleavage of the NHCOOCH₂ group, generating NHCOO and CH₂ fragments, and this cleavage occurs via a homolytic pathway. The dynamic competition between main chain scission and radical recombination drives the complex pyrolysis network, with temperature governing product diversity. This work provides microscopic insights into PU thermal degradation, supporting applications in fire safety assessment and material recycling.