A comparative study on horizontal flame spread behaviors of thermoplastic polymers with different melt flow indexes under external radiation

Abstract

• Effects of thickness and external radiation on horizontal flame spread were investigated. • Relationship between flame spread rate and external radiation heat flux was obtained. • A prediction model for mass loss rate during horizontal flame spread under external radiation was developed. • Incident heat flux has a power-law relationship with dimensionless distance between flame front and sample edge. The flame spread behaviors of thermoplastic polymers are intimately related to the properties of the material itself and the external environment. In this study, three different thermoplastic polymers, polymethyl methacrylate (PMMA), polypropylene (PP) and polystyrene (PS), were used. Four different sample thicknesses (denoted by d , 1–4 mm) and five different external radiation heat fluxes ( q ″ ̇ e , 0.0–10.0 kW/m 2 , with an interval of 2.5 kW/m 2 ) were designed for the experiments. To explore the impacts of melt flow index, sample thickness and external radiation heat flux on horizontal flame spread of thermoplastic polymers, 60 experimental conditions were carried out by altering d and q ″ ̇ e . The experimental results show that the horizontal flame spread process of thermoplastic polymers presents three stages, a growth stage, a steady spread stage and a decay stage. The flame spread characteristics of thermoplastic polymers are significantly different, which are mainly reflected in the large difference in melt flow behavior. The effect of sample thickness on flame spread behavior is less evident than that of external radiation heat flux. A prediction model for the mass loss rate of thermally thin thermoplastic polymers under external radiation is established based on the heat and mass transfer analysis, which is in good agreement with the experimental results. In addition, the incident heat flux in the preheating zone has a power-law relationship with the dimensionless distance between the flame front and the sample edge on horizontal flame spread process of thermoplastic polymers. The results can provide reference for the practical application of thermoplastic polymers in building fire protection engineering.