Objective Polyethylene terephthalate (PET) is a very widely used polyester fiber material, but PET-based materials have problems of being flammable or combustible, so low toxicity, low smoke and flame retardant lasting [(6-oxygen generation-6H-dibenzo [c, e] [1,2] -6-group) methyl] butanedioic acid (DDP) is selected as a flame retardant to PET. The purpose of studying the synthesis kinetics of PET is to effectively regulate the reaction rate, reaction conditions, product quality and other process parameters, and explore the internal law of polyester synthesis reaction, so as to guide the actual production process of polyester. Method This study chose copolymeric flame retardant PET as an example of trace modified polyester, prepared different DDP added flame retardant polyester, studied the two phases of esterification and condensation, explored the different condensation temperature, different flame retardant added on the synthetic reaction kinetics, in order to achieve the purpose of process regulation through production amplification. The thermal properties, crystallization properties, flame retardant properties and mechanical properties of flame retardant PET were characterized by testing differential scanning calorimetry, extreme oxygen index, conical calorimeter, scanning electron microscope, energy dispersive spectrometer and microinjection molding instrument. Results The activation energy (Ea) of the flame retardant PET with different phosphorus contents of the esterification reaction was gradually decreased from 81.37 kJ/mol to 59.52 kJ/mol with increasing amount of DDP addition at the same reaction temperature. For the same polymerization system, the increase in condensation temperature led to greater reaction rate constant and faster reaction speed. At the same condensation temperature, for different polymerization systems, the reaction rate was constantly decreased and Ea was significantly increased from 69.67 kJ/mol to 223.49 kJ/mol. With the increase of DDP addition, the cold crystallization temperature (Tcc) was increased from 121 ℃ to 143 ℃, the melting temperature (Tm) from 249 ℃ to 224 ℃, and the thermal crystallization temperature (Tmc) from 198 ℃ to 169 ℃. At the same condensation temperature, with the increase of DDP addition, LOI was gradually increased. When the phosphorus content was 1.10%, LOI reached 34%, and LOI did not change significantly. At the same condensation reaction temperature, the ignition time (TTI) was gradually increased to 57 s with the increase of DDP addition, and when the condensation reaction temperature was 270, 275, and 280 ℃, the peak heat release rate (pHRR) and the total heat release amount (THR) were significantly reduced. C and O were the residual carbon of PET, while the residual carbon of flame retardant PET was composed of C, O and P elements, and with the increase of DDP addition, the content of O and P were increased to 13.69% and 9.18%, respectively. PET showed more and denser residual carbon holes, while after DDP with phosphorus content of 0.65% was added, the holes of the residual carbon surface were significantly smaller, but the number of holes was not significantly improved. When the phosphorus content was increased to 1.10%, the number of residual carbon holes was greatly reduced, and the surface of the carbon layer became smoother and more compact with certain isolation effect. After the addition of flame retardant DDP, the elastic modulus of the polymer was increased from 947.3 MPa to 1 103.1 MPa, and with the addition of flame retardant DDP, the fracture elongation of the polymer was decreased from 247% to 190%. Conclusion Compared with PET, the addition of DDP promoted the positive esterification reaction but hindered the polycondensation reaction, and the flame retardancy of PET-DDP was significantly improved, and the change of polycondensation reaction temperature had less influence on the flame retardancy. In conclusion, the study on the kinetics of esterification and polycondensation reactions and the flame-retardant properties of PET-DDP provides data support for the adjustment of process parameters in the later industrial production of flame retardant polyester. © 2024 China Textile Engineering Society. All rights reserved.
