Development of a pyrolysis model for poly(vinylidene fluoride-co-hexafluoropropylene) and its application in predicting combustion behaviors

Pyrolysis and combustion behaviors of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a promising polymer matrix in lithium-ion polymer battery, are experimentally and numerically investigated. A pyrolysis reaction scheme consisting of three high order consecutive reactions was established based on the thermogravimetric analysis (TGA) measurements and parameterized combining a modified numerical model and Genetic Algorithm (GA). The results show that in the heating rate range of 5–20 K min⁻¹ the peak temperature of pyrolysis increases from 739 to 770 K. After deriving the pyrolysis kinetics, the thermodynamics was further determined by inversely modeling the measured mass loss rate in cone calorimeter tests. By fitting the measured heat release rate, the effective heat of combustion of each gaseous component, the global effective heat of combustion (9.56 MJ kg⁻¹) and the flame heat flux (15 kW m⁻²) were quantitatively estimated. Reliability of the fully developed model was validated by alternative experimental results which were not utilized in parameterization, and good agreement was found. The collected ignition times in cone calorimeter tests were well predicted by the numerical model employing the measured critical mass flux, 2.87±0.32 g m⁻² s⁻¹. By invoking the ignition theory proposed for thermally intermediate solid and the measured ignition data, thermal diffusivity of PVDF-HFP, critical heat flux and critical temperature were assessed to be 3.00 × 10⁻⁷ m⁻² s⁻¹, 17.13–24.34 kW m⁻² and 763.34–794.13 K, respectively.