Simultaneously improving the fire performance and toughness of polylactic acid by reactive blending with castor oil-based polyurethane and ammonium polyphosphate

A new method has been presented to simultaneously enhance both the flame retardancy and toughness of polylactide acid composites by introducing castor oil-based polyurethane and ammonium polyphosphate via reactive blending. The in situ polymerization of castor oil and toluene diisocyanate in the polylactide acid matrix has been confirmed by the Fourier transform infrared spectroscopy. The flame retardant test results indicate that the introduction of 20% ammonium polyphosphate can increase the limiting oxygen index of polylactide acid composites from 19.3% to 27.2%, upgrade the UL-94 rating from no rating to V-0, and decrease the peak heat release rate from 505.5 to 337.0 kW/m². Moreover, the toughness of polylactide acid is also improved significantly, with the elongation at break and notched impact strength increasing to 37.0% and 7.59 kJ/m², respectively. The possible mechanisms for both flame retardancy and toughness are also discussed and proposed.