Ignition and combustion behaviors of carbon fiber reinforced polypropylene: Impact of fiber content and size

Carbon fiber reinforced polypropylene (CFRP) composites are widely used in various applications due to its prominent merits, whereas quantitative modelling of their thermal response is insufficiently reported. To challenge this issue, CFRP samples with 5–20 wt% carbon fiber (CF) content were prepared to conduct ignition and combustion tests under heat fluxes of 20–40 kW/m². Meanwhile, CF sizes of 1000 and 100 mesh were adopted to examine their impact on flammability. A 1D condensed phase numerical model incorporating pyrolysis, heat transfer, surface and in-depth absorption of radiation was developed to simulate experimental results. Thermodynamics of PP were determined by inversely modelling measured temperature in ignition tests. Flame feedback heat flux was assumed to linearly depend on measured mass loss rate (MLR), which provided high predictive accuracy of combustion results. Effective heat of combustion (EHC) was estimated and used to simulate measured heat release rates (HRR). Furthermore, smoke production rate (SPR), CO and CO₂ production rates (PR_CO and PR_CO2) are elaborated. The results show that CFRPs exhibit higher top surface temperature (T_top) and accelerate ignition compared with PP. Limited irregular variation of T_top is observed with varying CF contents. Peak values of MLR and HRR decline with higher CF content, whereas combustion time keeps approximately unchanged. EHC is found independent of CF content, yielding an average value of 52.6 MJ/kg. CF size exerts little effect on ignition and combustion of CFRPs. The numerical model captures all crucial measurements in ignition and combustion tests despite some minor deviations. Measured SPR, PR_CO and PR_CO2 curves share many similarities to those of the related MLR and HRR profiles.