Construction of gas-solid synergistic high-efficiency flame-retardant PET based on side chain phosphorus containing monomers for transparent ultra-thin casings with flame retardancy

Polyethylene terephthalate (PET) has a wide range of applications in human life due to its high-cost performance, but its poor brittleness and flame retardancy limit its scope of application, especially in the ultra-thin configuration required for advanced electronic products. Here, focused on the flame-retardant PET-based copolyesters with advantages in industrial prospects, a one-pot, two-step method is utilized to incorporate 1,4-cyclohexanedimethanol (CHDM) and pre-modified Dihydro-10-[2,3-di(hydroxycarbonyl) propyl]-10-phosphaphenanthrene-10-oxide (DDP) with terminal hydroxyl groups (named DDP-EG) into the PET main chain, resulting in the formation of a PEDCTs copolyesters with improved overall performance. The phosphorus-containing and halogen-free flame retardant DDP-EG embedded in the polymer backbone can achieve free radical quenching in the gas phase and catalytic charring formation in the condensed phase. PEDCTs exhibit remarkable flame resistance and fire protection, maintaining a UL-94 V-0 rating at 0.8 mm thickness, while enhancing the limiting oxygen index to 32.0%. The PHRR (peak heat release rate) decreases by 49.0%, and the total heat release (THR) diminishes by 31.0%. In addition, the fire safety parameter FGI dropped from 8.03 to 4.59, and the FPI increased from 0.042 to 0.105. Moreover, PEDCTs maintained a high light transmittance (89.6% at 700 nm) and an elongation at break of 150%.