Effects of phosphorus-containing thermotropic liquid crystal copolyester on pyrolysis of PET and its flame retardant mechanism

In order to compare their inherent flame retardancy and thermal stability, two phosphorus-containing thermotropic liquid crystalline copolyesters (P-TLCP) were synthesized by melting transesterification. Additionally based on the facts that the P-TLCP can work as a functional additive to enhance the flame retardancy and mechanical property of PET, we further studied the flame retardant mechanism. Scanning Electronic Microscope (SEM) observations show that the char from PET/P-TLCP is more compact, therefore more efficiently resists fire and heat attack than pure PET. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) measurements of evolved gas, indicate that P-TLCP decomposes to produce phosphorus-containing small molecular compounds during the pyrolysis process, such that P-TLCP could play a flame retardant role in vapour phase. Furthermore, P-TLCP strongly inhibits the generation of combustible compounds in the pyrolysis of PET, which also helps to resist fire propagation.