Fabrication of novel macromolecular P–S synergistic flame retardants and its applications in biodegradable poly (lactic acid): Combustibility, anti-melt dripping behavior, crystallization, and mechanical properties

Abstract

As a biodegradable material, polylactic acid (PLA) has very bright application prospects, but its high flammability and poor crystallinity limit its use in electronics, automotive components, and other applications. In this paper, a macromolecular P–S synergistic multifunctional flame retardant (PTP) was obtained by an easy one-pot approach using polyethyleneimine, thiophene-2-formaldehyde and phytic acid. The addition of PTP to PLA improved the combustion resistance, anti-melt dripping and crystallization performance. The PLA compounds attained UL-94 V-0 grade at an ultra-low load (3 wt%) of the PTP, and the limiting oxygen index improved to 28.3 % when added at 9 wt%. The effective heat combustion and the total heat release value of PLA/9PTP composite were reduced from 24.4 and 93.1 to 18.9 MJ/kg and 86.0 MJ/m2, respectively. PLA/PTP composites provided a denser and more stable char layer during combustion than PLA and emitted significantly less-flammable gaseous volatiles. Meanwhile, PTP significantly facilitated the nucleation and crystallization of PLA, and the crystallinity elevated from 2.9 % to 35.5 % while the crystallization half-time reduced to 3.3 min about 10 % of pure PLA at 110 °C when added at 3 wt%. Besides, as PTP was a macromolecular flame retardant, PLA/PTP composites still maintained superior mechanical properties with the addition of PTP. This article gave an easy and effective way to fabricate PLA compounds with excellent flammability resistance, anti-dripping, crystallization and mechanical performance, which may be helpful for extending practical applications of PLA materials.