Diphenolic acid based biphosphate on the properties of polylactic acid: Synthesis, fire behavior and flame retardant mechanism

In an effort to impart fire protection properties to polylactic acid (PLA) utilizing renewable resources, diphenolic acid, a plant derived compound, was used to synthesize a biphosphate (hereinafter shortened as FR) that contains two types of phosphorus. The chemical structure of FR was confirmed by H-1 NMR and P-31 NMR. UL-94 V0 rating and LOI value of 27.4 for PLA were achieved at the FR loading content of 16 wt%. Besides, the heat release rate and total heat release of the flame retardant PLA were decreased remarkably in cone calorimetric tests. The significantly increased CO/CO2 ratio in cone tests and the presence of phosphorous containing compound in gas phase in TG-FTIR tests confirmed that the gas phase mechanism is mainly responsible for the improved flame retardant performance. Differential scanning calorimetric analysis showed the glass transition temperature of PLA composites have no change indicating no plasticizing effect of the FR. Finally, the tensile tests revealed that the ductility of PLA was sustained and tensile strength was depressed in a minimal content after the FR was incorporated. This work suggests a novel green strategy for improving flame retardancy performance of PLA and promoting the utilization of sustainable resource. (C) 2016 Elsevier Ltd. All rights reserved.