Construction and verification of a heat transfer-combustion model for EP/BNNS composite material based on analysis of the char layer dynamic evolution

A stratified char structure with porous upper and dense bottom layers was established. • A heat transfer–combustion model considering char layer stratified structure was developed. • Porosity-dependent thermophysical properties were incorporated into heat transfer modeling. • The model accurately predicted temperature, mass loss and heat release behavior. • The proposed model provides a practical tool for thermal engineering design of flame-retardant polymer components. Accurately describing the char layer dynamic evolution is a key step to further understand the flame retardancy mechanism of charring flame-retardant polymer material. Epoxy resin (EP) and boron nitride nanosheets (BNNS) was used to prepare EP/BNNS composite materials. An in-depth investigation was conducted on char layer dynamic evolution of EP/BNNS composites during burning by macroscopic observation and microscopic characterization such as using SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infrared Spectroscopy) techniques, where the char layer was obtained from different combustion phases. An interesting phenomenon was observed that a porous upper part and a dense bottom part of the char layer structure was formed gradually in the char layer dynamic evolution process. Accordingly, a stratified structure char layer model with porous in the upper part and dense in the bottom part was developed and porosity was tested for each part. Subsequently, a heat transfer-combustion physical and mathematical model of EP/BNNS composites was established, which considered the proposed stratified structure char layer model. The simulation results showed that the root mean square errors of the temperature field, mass loss rate, and heat release rate were 46.76 °C, 0.23 mg·cm −2 ·s −1 , and 95.48 kW·m −2 , and the simulation results had a high degree of agreement with the experiment results.