Influence of a Phenethyl-Bridged DOPO Derivative on the Flame Retardancy, Thermal Properties, and Mechanical Properties of Poly(lactic acid)

A phenethyl-bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (DiDOPO) was synthesized and characterized. The effects of DiDOPO on the fire resistance, thermal performances, and mechanical performances of poly(lactic acid) (PLA) were examined. PLA/10 wt % DiDOPO obtained the V-0 rating (UL-94) at thicknesses of 3.2 and 1.6 mm with an increased limiting oxygen index value of 27.1%. The incorporation of DiDOPO evidently prolonged the ignition and decreased the peak heat release of PLA. Moreover, PLA/DiDOPO had higher thermal stability than neat PLA especially under the air condition. The added DiDOPO could obviously change the crystallization properties of PLA. In addition, the flexural strength of PLA composites increased by 15.8% with 10 wt % loading of DiDOPO. Rheological analysis indicated that DiDOPO suppressed the melt dripping of PLA by enhancing the melt stability, which was caused by a continuous morphology of DiDOPO in PLA. Overall, DiDOPO is a good flame retardant with a potential application for PLA.