Pyrolysis and combustion characterisation of HDPE/APP composites via molecular dynamics and CFD simulations

Understanding and characterisation of the pyrolysis and burning behaviour of flame retardant (FR) polymers are essential towards optimising the end-product in terms of flammability, charring, toxicity and smoke reduction. This study proposes a modelling framework to study the combustion behaviour, pyrolysis kinetics and FR mechanisms of FR treated polymer composites. This numerical framework has utilised reactive molecular dynamics (MD-ReaxFF) simulations to characterise the pyrolysis kinetics, char formation and residues fragments of High-density polyethylene (HDPE) and Ammonium polyphosphate filled HDPE (HDPE/APP) composites. Through MD characterisation of the polymer breaking process, thermal degradation behaviours are described by reactions rates in Arrhenius form and subsequently imported into the computational fluid dynamics (CFD) models. The modelling framework has well-predicted the heat release rate (HRR) profiles, ignition time and combustion duration of the HDPE and HDPE/APP composites, where average relative errors less than 15% were achieved compared to thermogravimetric analysis (TGA) and cone calorimeter tests. The proposed numerical framework demonstrated the capability to capture the burning behaviour and flammability of FR treated polymer composites and identify the pyrolysis kinetics and FR mechanisms offered by the APP additives, such as dehydration and char formation.