Improvement of Flame Retardancy and Antidripping Properties of Intumescent Polybutylene Succinate Combining Piperazine Pyrophosphate and Zinc Borate

Developing flame-retarded polybutylene succinate (PBS) is a challenging task owing to its high flammability, noncharring, and melt-dripping during burning. In this work, based on the synergistic combination between piperazine pyrophosphate (PAPP) and zinc borate (ZnB), a promising intumescent PBS system was developed as an efficient strategy to impart PBS with improved flame retardancy and antidripping properties. The results showed that PBS/PAPP15%/ZnB5% passed V-0 rating in the UL-94 vertical burning test (3 mm), while only a V-2 rating was achieved for PBS/PAPP20%. Compared to PBS/PAPP20%, the combination of PAPP and zinc borate (ratio of 15:5) led to significant reductions in the peak heat release rate (pHRR, -55%), fire growth rate index (FIGRA, -40%), and maximum average rate of heat emission (MARHE, -47%) evaluated by mass loss cone calorimetry. Meanwhile, the flame retardancy index of PBS/PAPP15%/ZnB5% reached up to 5.18 and the flameout time significantly increased to 1049 s. Fourier transform infrared and solid-state nuclear magnetic resonance analyses were employed to gain insight into the reaction-to-fire mechanism in the condensed phase. The results confirmed the fact that the formation of a crack-free protective intumescent char layer, reinforced by thermally stable inorganic species (boron-zinc phosphates), effectively restricted the heat and fuel transfer between condensed and gas phases, hence resulting in the excellent enhancement in flame retardancy.

Automated summary

The combination of PAPP and zinc borate significantly enhances the flame retardancy of PBS, leading to reductions in peak heat release rate, fire growth rate index, and maximum average rate of heat emission. It also improves the flame retardancy index and flameout time significantly.