Preparation of PBAT Copolyesters with Flame Retardant and Degradable Functions through PBT Chemical Alcoholysis and Closed-Loop Recycling

The issue of fire hazard safety with regard to materials is of great concern. Polybutylene terephthalate/butylene terephthalate (PBAT) is the most extensively researched and utilized biodegradable material. However, the absence of flame-retardant chain segments in its molecular structure poses a significant environmental safety hazard. Our team utilizes the reversibility of the polymerization reaction of PBT (polybutylene terephthalate) materials and a chemical recycling process to degrade PBT into BHBT (butylene terephthalate), a raw material for the preparation of PBAT. At the same time, together with the halogen-free and environmentally friendly flame-retardant CEPPA (3-hydroxyphenylphosphinyl-propanoic acid) and BHAT (butylene glycol adipate), we design and produce an environmentally friendly and highly efficient halogen-free flame-retardant PBAT copolyester (PBATcept). The closed-loop recycling of nonbiodegradable PBT materials into small-molecule oligomers (BHBT) and oligomers into PBATcept was realized. The successful introduction of CEPPA into the PBAT chain segment was demonstrated to result in a reduction in the crystalline properties of PBATcept and an improvement in transparency and flame retardancy. The introduction of 5.0 mol % CEPPA resulted in a tensile strength of 10.93 ± 0.97 MPa and an elongation at break of 830.40 ± 48.25% for PBATcept5.0. Furthermore, the LOI value is 32.0%, and the UL-94 rating is V-0. CEPPA exerts synergistic flame-retardant effects of gas-phase flame retardancy and condensed-phase flame retardancy in PBATcept. During combustion, CEPPA undergoes preferential decomposition, generating nonflammable gases (H₂O and CO₂) to impede combustion and dilute the concentration of flammable gases. Concurrently, it forms a dense carbon layer on the surface of the polymer, which mitigates the safety hazards associated with PBAT due to fire. Furthermore, the preferential hydrolysis of the flame retardant enhances the biodegradation performance of PBATcept. The relative biodegradation rate can reach 33.92% after 30 days when the addition amount of CEPPA is 10.0 mol %.