Influence of two-phase structure of PET/PPSU alloys and selective distribution of flame retardants on the flame retardancy of polymer alloys

Polymer alloys can obtain the excellent performance of a variety of polymers. The polymer blending system has been studied by many scholars, especially the multi -component system containing additives, which is receiving more and more attention from researchers. The flame retardancy behavior of polyethylene terephthalate (PET)/ Polyphenylene sulfone (PPSU) blends containing A 9,10-dihydro-9-oxa-10 phosphophenanthrene-10-oxide based derivative tris-(3-dopo-propyl) -triazine trione (TAD) is explored. Flame retardancy of PET/PPSU composite was characterized by Limiting oxygen index (LOI), vertical combustion test (UL 94), and cone calorimeter test. PPSU is a less flammable material with an LOI value of 40.0 % when used alone. With a 5 % flame retardant TAD addition, the LOI value of the PPSU/TAD-5 composite can be increased to 42.6 %. Interestingly, the LOI of PET with 5 wt% of TAD was 30.2 %, whereas the LOI of PET/PPSU(70/30) composites with the same 5 wt% of TAD was reduced to 26.3 %. We investigated by SEM-EDS that the flame retardant TAD always preferred to be distributed in the PPSU phase in PET/PPSU composites with different ratios. When PPSU was wrapped by the PET phase, which is the sea structure, the flame tended to follow the sea structure combustion channel of the polymer alloys during combustion, and the island structure of PPSU had little effect on the overall flame retardancy of the polymer alloys. Similarly, when PPSU becomes a continuous matrix, even without flame retardant, it significantly reduces the combustibility of the blends. However, with the addition of flame retardants, most of the flame retardants are distributed in the PPSU matrix, which significantly increases the LOI value of the PET/PPSU(40/60)/TAD-5 composite. Therefore, we conclude that there is an uneven distribution of flame retardants in the two phases, so for polymer alloys, the distribution of flame retardant in the two phases, as well as the construction of the continuous phase and the dispersion phase, determine the overall flame retardant properties of the composites.