Exploring reaction mechanisms and kinetics of cellulose combustion via ReaxFF molecular dynamics simulations

Abstract

The incorporation of natural fibers, represented by cellulose fibers, into functional composites for construction applications has garnered widespread attention due to their renewability and sustainability. However, their flammability raises concerns around fire safety. To investigate further the combustion mechanism and kinetics of cellulose, molecular dynamics simulations equipped with reactive forcefield (ReaxFF) are conducted on active cellulose polymers. High-temperature ReaxFF simulations are characterized by effective collisions that better approximate reality. The detailed reaction scheme revealed by the simulations is consistent with the experimental results. The formation of main combustion products, such as carbon monoxide, carbon dioxide, and water, highly depends on free radical reactions. Toxic species such as formaldehyde, glycolaldehyde, and carbon monoxide can be inhibited through effective control of hydroxymethyl, acetyl, and formyl radicals. A higher effective collision proportion promotes combustion, mainly through the enhanced activity of free radicals such as hydroxyl groups. Besides, increased oxygen coefficients have a negligible effect on the final combustion products under oxygen-rich conditions, although intermediates show noticeable sensitivity to oxygen. A kinetic analysis of the initial decomposition and intermediate reaction stages of cellulose combustion is presented, yielding reaction rates consistent with first-order reaction kinetics. This study provides atomic-level insights into cellulose combustion and lays a foundation for predicting the detailed combustion chemistry of cellulose-based materials, which can inform a material design aimed at better fire resistance.