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

In this research, Fe 3+ , Al 3+ , and Cu 2+ 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 Fe 3+ would coordinate with the C O 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 Fe 3+ 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 Cu 2+ 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). • Thermal degradation mechanism of Fe-MOF and PET composites was studied using quantum chemical calculation coupled with Py-GC-MS and TG-IR experimental. • The flame retardant order for different cationic MOF-PET was predicted via DFT calculation as following: Fe-MOF-PET > Al-MOF-PET > Cu-MOF-PET. • The order was proved by the CONE, LOI and VFT test. • Cu-MOF-PET proceed a “one point” fracture reaction pathway while it indicated “two points” fracture for Fe-MOF-PET and Al-MOF-PET.