Study on flame retardancy and smoke suppression of PET by the synergy between Fe 2 O 3 and new phosphorus-containing silicone flame retardant

Abstract

To reduce the environmental hazard from the flame retardant, a halogen-free phosphorus-containing silicone flame-retardant poly N,N dimethylene phosphate aminopropyl siloxane (PDPSI) was prepared following the Mannich reaction. Then, PDPSI and ferric oxide (Fe₂O₃) were used for the preparation of synergistic flame-retardant polyethylene terephthalate (PET). The flame-retardant test results revealed that at 2% PDPSI/Fe₂O₃ content and 1:2 mass ratio of PDPSI to Fe₂O₃, the limit oxygen index value of the PDPSI/Fe₂O₃/PET composite material was 27.9%, reaching the flame-retardant level and passing the V-0 rating in the UL-94 test. In addition, the PDPSI/Fe₂O₃/PET composites had a char residue content of 17.5% at 700°C, an increase of 30.6% compared to that of the pristine PET. In the cone calorimeter test, the addition of PDPSI/Fe₂O₃ significantly reduced the peak heat release rate (PHRR), total heat release (THR) rate, and total smoke production (TSP) value of the resulting PET composites. PHRR and THR decreased by 66.05% and 14.3%, respectively. The TSP value decreased from 14.4 m² to 8.1 m², a decrease of 43.8%. The scanning electron microscopy images and Fourier-transform infrared spectra of the char residue showed a significant synergy between Fe₂O₃ and PDPSI, changing the structure of the carbon layer in continuous and dense form, thus the flame retardancy and smoke suppression of the PET composites improved. In addition, the tensile strength of the PET composite was 42.11 MPa, which was only 1.84% less than that of the pristine PET.