Thermal degradation and flame retardancy prediction of Fe, Al, and Cu-based metal-organic framework and polyethylene terephthalate nanocomposites using DFT calculation

Abstract

In this research, Fe3+, Al3+, and Cu2+ containing MOFs were synthesized and added into polyethylene terephthalate (PET), respectively, namely Fe-MOF-PET, Al-MOF-PET, and Cu-MOF-PET. Fe-MOF-PET was studied as the model sample to discuss the effect of metal cations of MOF on the thermal degradation mechanism. It indicated that Fe3+ would coordinate with the CO of PET and attract the C–O bond of the ester group to occur the homolytic reaction according to quantum chemical simulation combining the experimental data, including the pyrolysis chromatography-mass spectrometry (Py-GC-MS) and thermogravimetric infrared spectroscopy (TG-IR). Furthermore, the thermal degradation reaction of Fe3+ as the standard pathway was applied to predict flame retardant properties of different MOF-PET composites. The flame retardant order, Fe-MOF-PET > Al-MOF-PET > Cu-MOF-PET, was also successfully proved by the cone calorimeter (CONE), limiting oxygen index (LOI), and vertical flame test (VFT), respectively. The worse result of Cu2+ was attributed to the “one point” fracture reaction pathway of Cu-MOF-PET, which was different from the “two points” fracture of Fe-MOF-PET and Al-MOF-PET. This research provided an effective tool for predicting the flame retardant properties of MOFs in different polymer matrix using density functional theory (DFT).