Comparative study on the flame retarded efficiency of melamine phosphate, melamine phosphite and melamine hypophosphite on poly(butylene succinate) composites

The main aim of this work was to investigate the flame retarded efficiency of melamine phosphate (MP), melamine phosphite (MPi) and melamine hypophosphite (MHP) on poly(butylene succinate) (PBS) composites. The flame retardant, thermal degradation and combustion properties of PBS composites were characterized by limiting oxygen index (LOI) test, vertical burning (UL-94) test, thermogravimetric analysis (TGA) and cone calorimeter (Cone), respectively. The LOI results showed that the LOI values followed the sequence of PBS/MP < PBS/MHP < PBS/MPi at the same additive loadings. TGA results indicated that the initial decomposition temperature of PBS composites decreased with the decrease of phosphorus valence state and the incorporation of all three compounds could promote the char formation. Adding these three compounds into PBS matrix can decrease the peak heat release rate (PHRR) obviously from cone calorimeter results. Scanning electron microscopy (SEM) was employed to characterize the morphology and structure of the char residues. The flame-retardant mechanism in gaseous phase and condensed phase were investigated by thermogravimetric analysis/infrared spectrometry (TG-IR) and in situ Fourier transform infrared spectroscopy (in situ FTIR), respectively, and the possible flame-retardant mechanism was proposed.