Development of flame retardants for poly(lactic acid) bioplastics using bio-based oil

This study presents the development of a bio-based flame retardant derived from renewable soybean oil to improve the flame retardant performance of poly (lactic acid) (PLA). Soybean oil phosphate ester (SOPE) was synthesized from epoxidized soybean oil (ESO) and incorporated into PLA at loadings of 0.5–2 phr via twin-screw extrusion. FT-IR and NMR analyses confirmed the successful synthesis of SOPE. Thermal analysis revealed that the incorporation of SOPE influenced the thermal degradation behavior and crystallization properties of PLA. PLA containing 2 phr SOPE achieved a limiting oxygen index (LOI) value of 26% and attained a V-0 rating in the UL-94 vertical burning test, indicating effective flame retardancy at a low loading level. TGA results showed a relatively low char yield, suggesting that the flame retardant mechanism did not predominantly occur in the condensed phase. Py-GC/MS analysis detected phosphorus-containing radical species (PO• and PO 2 •), indicating that the flame retardant action mainly proceeded via a gas-phase radical trapping mechanism. However, the incorporation of SOPE led to a reduction in molecular weight and mechanical properties due to the hydrolytic degradation of PLA. Overall, the results demonstrate that soybean oil–derived phosphate ester can serve as a bio-based and effective flame retardant for PLA.