Fully Bio-Based Phytic Acid–Basic Amino Acid Salt for Flame-Retardant Polypropylene

Phytic acid and amino acid belonging to the biomass material have a wide range of sources in nature. In this work, three kinds of basic amino acids, which are arginine, lysine, and histidine, were used to prepare different bio-based phytic acid–basic amino acid salts (PaArg, PaLys, and PaHis) via a salt-forming reaction. After the incorporation of PaArg, PaLys, and PaHis into polypropylene (PP), PaArg showed a higher efficiency than PaLys and PaHis in endowing PP with flame retardancy. At 22 wt % PaArg, the limiting oxygen index (LOI) value of functional PP was 26.0%, and its UL-94 rating reached V-0 in the vertical burning test. In the fire hazard test, PaLys showed a higher efficiency than PaArg and PaHis in reducing the fire hazard of PP during burning. The peak value of the heat release rate for PP containing 25 wt % PaLys was decreased by 70.7% compared with that of PP, and its fire growth rate was reduced by 86.9%. Analysis on the fire-safety mechanism revealed that the high char-forming rate and the quality of the residue dominated the superior flame-retardant efficiency of PaArg in UL-94 and LOI tests; high strength of the formed char layer, diluting effect of nonflammable gases, and incomplete combustion action led to the superior efficiency of PaLys in decreasing the fire hazard of PP. This work confirms that fully bio-based phytic acid–basic amino acid salt based on the accurate molecular design may endow PP with fire safety under different burning scenes.