Polylactic acid (PLA) is an attractive biomass-sourced thermoplastic polymer because of its similar strength and modulus to polystyrene, in addition to its biodegradable and biocompatible nature. However, it is inherently flammable, which makes materials made of it a fire hazard. In this study, bio-sourced additives – epoxidized tannic acid (ETA) and phytic acid-lysine (PALys) salt – were synthesized to form a flame retardant (FR) system. The former has two functions: anchor and carbon source. The epoxy group of ETA reacts with the end groups of PLA and OH groups of PALys, which prevents the additives from leaching out; tannic acid itself is known for excellent char formation during combustion which makes it a good carbon source. The latter is a phosphorous-nitrogen flame retardant system wherein phosphorous functions as a catalyst for carbonization and nitrogen serves as a dilution agent during burning. A twin-screw extruder was used to compound the additives with PLA; and the design of experiment (DOE) with a 2x2 planning matrix was utilized to analyze the micro combustion calorimeter peak heat release rate (an FR basis) and determine the most significant factor affecting the flame retardant performance of the composites. The half-normal plot indicated that the PALys concentration in the PLA/ETA/PALys system was the most significant factor in producing an effective FR system. In testing the system with increasing PALys concentration (1 wt% to 5 wt%), it was determined that PLA/1 wt% ETA/5 wt% PAlys has the best FR performance with a V-0 UL94 rating, 34% limiting oxygen index, 50% reduction in burn time, and improved charring and thermal stability. Furthermore, the flame retardant mechanism was also established in this study. Future research on this system will focus on the effect of processing on FR performance, as ETA is also capable of being as a chain extender.
