Synthesis of phytic acid-based compounds for improving the mechanical properties and fire performances of poly(lactic acid)

Bio-based phytic acid is a nontoxic naturally occurring compound and has the potential for use in polymers for flame retardancy due to its high phosphorus content. In this work, two novel phytic acid-based compounds, phytyl octyl glycidyl ether (PAOc) and phytyl phenyl glycidyl ether (PAPh), were prepared through the addition esterification of 2-ethylhexyl glycidyl ether and phenyl glycidyl ether with phytic acid. The chemical structure of PAOc and PAPh were confirmed by H-1 NMR, P-31 NMR, and FTIR spectra. The mechanical, thermal, and fire performances of the PLA/PAOc and PLA/PAPh blends were investigated by various tests including mechanical, thermal (DSC, TGA), morphological (SEM), and flammability (LOI, UL-94). The results showed that the addition of PAOc and PAPh improved the thermal stability of PLA through hydrogen bonding. PAPh was more effective to improving the mechanical properties and crystalline properties of PLA than PAOc. When PAPh was 5 wt%, the elongation at break of PLA increased from 2.9% to 16.7%, the tensile strength increased from 32 to 37 MPa, and the crystallinity increased from 30.6% to 36.7%. Moreover, introduction of phenyl group was beneficial to phytic acid improving the flame retardant properties of PLA. At an addition level of 10 wt%, the LOI of PLA/PAPh reached 27.5% and achieved UL-94-V0 rating while improving the mechanical properties.