Preparation of green biodegradable lactic acid-based flame-retardant plasticizer for simultaneously enhancing flexibility, flame retardancy, and smoke-suppression of poly(lactic acid)

Conventional petroleum-based plasticizers not only exhibit reproductive toxicity and non-biodegradability, but their introduction also makes plastics highly combustible. Therefore, the development of biodegradable flameretardant plasticizers derived from biomass resources can effectively solve the matters mentioned above. In this work, we developed a new l-lactic acid-based biodegradable flame-retardant plasticizer containing phosphorus, nitrogen, and silicon elements (PDL550) with flame-retarded, smoke-suppressing, and plasticized function. The introduction of PDL550 can simultaneously enhance the flame-retardant and flexible performances of polylactic acid (PLA). With the addition of 20 phr PDL550, the PDL550-plasticized PLA blends could pass a UL94 V-0 grade, and simultaneously its elongation at break increased to 290.32 % in comparison with that of pure PLA (3.70 %). The cone calorimetric tests exhibited that the peak of heat release rate and total heat release of PDL550-plasticized PLA blends, in comparison with that of pure PLA, decreased by 17.8 and 50.8 %, respectively. By analyzing the volatiles and the residual char layer, the phosphorus and silicon elements synergistically in PDL550 are conducive to facilitating the formation of the complete and dense char layer, thus suppressing the release of smoke and shielding the attack of heat. Interestingly, the active soil and tenebrio molitors experiments exhibited that the PDL550 chain was attacked by microbes to form a small aliphatic molecule structure, indicating the excellent biodegradability of PDL550. This study provides an essential reference for developing bioderived fire-retardant plasticizers to enhance fire safety, smoke-suppressing, and flexible PLA composites.