Study on the synergistic flame-retardancy of phenyl/vinyl siliconesquioxane and aluminum diethyl phosphinate on polyethylene terephthalate

Polyethylene terephthalate (PET), a widely used engineering thermoplastics, is inherently flammable, presenting significant fire risks. Aluminum diethyl phosphinate (ADP) is widely used in PET, while they tend to increase smoke hazards in its flames retardancy. A novel flame-retardant ladder phenyl/vinyl polysilsesquioxane (VPPSQ) acting as both a charring flame retardant and smoke suppressant was introduced into the PET/ADP composites. For PET/ADP6/VPPSQ4, the limiting oxygen index increased to 32.8 % from 23.3 %, and the amount of heat and smoke released was significantly reduced, compared with neat PET. Additionally, the hazard of dripping was eliminated and the UL 94 rating reaches to V-0 level. This work provides a new strategy for eliminating multiple fire hazards of smoke, heat and dripping of PET. The gas phase flame retardancy effect of ADP is primarily present during the initial stages of combustion, with the carbonization action of ADP becoming more crucial during the middle and later stages of burning. However, the char layer formed by PET/ADP is unstable and undergoes further degradation. When VPPSQ is introduced into PET/ADP, the pyrolysis products of VPPSQ, including silicon fragments, SiO₂, and graphitized structures, significantly enhance the thermal stability and barrier effect of the char layer.