Preparation and Characterization of a Latent Reactive Organo-phosphor us-nitrogen Flame Retardant and its Applications in Polylactic acid Syst ems

Abstract

Abstract In this study, an organophosphorus-nitrogen compound with latent reactive flame retardant properties(LROPN) were prepared by a facile method using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO), 4,4 ′-diphenylmethane diisocyanate(MDI) and ethanol as raw materials. The structure of the resulted compound were characterized by infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR). The performances of LROPN used for Polylactic acid (PLA) were investigatd by the technologies of vertical combustion (UL-94) and limiting oxygen index (LOI) test. The results showed that adding LROPN into PLA matrix could significantly improve the flame retardancy of PLA. The LROPN addition of 8(wt)% could reach UL-94 V0 level, and the LOI increased from 19.5% to more than 26%. The TG-FTIR spetra of LROPN indicated that LROPN can deblock at around temperature of 180oC, which indicating LROPN have latent reactivity. The TG-DTA data showed that the maximum weight lost peak LROPN/PLA systems occured at temperature around 363 oC, and the amount of the residue carbon reached 3.93% when the content of LROPN was 8(wt)%. The scanning electron microscopy(SEM) morphologies showed that the addition of LROPN helped to reduce the melt driping of LROPN/PLA systems. The mechanism of flame retardant was investiated based on the TG-FTIR spetra of LROPN, the TG-DTA data of LROPN/PLA systems, and SEM morphologies of residue carbon. The flame retardancy mechanism of LROPN included the combination of free radical suppression and inert gas in the gas phase, and the barrier effect of coke residue in the condensed phase.