Simultaneously enhanced fracture toughness and flame-retardant property of poly(l-lactic acid) via reactive blending with ammonium polyphosphate and in situ formed polyurethane

The preparation of poly( l -lactic acid) (PLLA) with high mechanical and ideal flame-retardant properties is a great challenge. Herein, a simultaneous toughness and flame-retardant PLLA composite was successfully fabricated by using a one-step process which introduces 4,4′-methylenediphenyl diisocyanate and ammonium polyphosphate (APP) into PLLA/poly(ε-caprolactone) blends. SEM, Fourier transform infrared spectroscopy and TGA were adopted to confirm that APP participated in the in situ reaction during the melt process. The impact strength was increased to 13.5 kJ m −2 from 1.0 kJ m −2 for L8P2A5 composite, indicating the toughening effect of reactive blending. The cone calorimeter test, limiting oxygen index and vertical burning test results indicate that the flame-retardant properties of the composites are enhanced with increasing APP content. This work provides a method to prepare PLLA with high mechanical properties and enhanced flame retardancy. © 2020 Society of Chemical Industry