Simultaneously enhancing the fire retardancy and crystallization rate of biodegradable polylactic acid with piperazine-1,4-diylbis(diphenylphosphine oxide)

The simultaneous improvement of flame retardancy and crystallization rate for polylactic acid (PLA) has always been a challenge in the field of engineering applications. In this paper, a piperazine-phosphamide derivative (PPDO) was successfully synthesized from diphenylphosphinyl chloride and piperazine and its chemical structure was confirmed. The PPDO was served as a multi-functional additive to simultaneously improve the fire safety and crystallization rate of PLA. The fire retardancy, crystallization behaviors, mechanical properties and flame-retardant mechanism of PLA biocomposites were systematically investigated. With the incorporation of mere 3 wt% PPDO, the PLA biocomposites fulfilled UL-94 V-0 rating with the LOI of 27.8%. The outstanding fire retardancy of PPDO in PLA was ascribed to the shielding effect of compact and dense char layer in condensed phase, and the suppression function of benzene- and phosphorus-containing free radicals and the dilution role of inert gases in vapor phase. Thus, the effective heat combustion and total heat release of PLA biocomposites were prominently depressed. Meanwhile, PPDO was a good nucleating agent for PLA, which effectively increased the crystallinity and crystallization rate of PLA. Besides, PLA biocomposites still maintained remarkable transparency and mechanical properties due to the low addition of PPDO and excellent compatibility with the PLA matrix, which endowed flame-retardant PLA biocomposites with the enormous application prospect in the field of advanced optoelectronic devices.