Coumarin-DPPO a new bio-based phosphorus additive for poly(lactic acid): Processing and flame retardant application
Daniele Roncucci, Marie-Odile Augé, Sithiprumnea Dul, Jiuke Chen, Ali Gooneie, Daniel Rentsch, Sandro Lehner, Milijana Jović, Alexandra Rippl, Vanesa Ayala, Fanny Bonnet, Serge Bourbigot, Hansjörg Grützmacher, Gaëlle Fontaine, Sabyasachi Gaan
Abstract
This study addresses very important aspects of the sustainable development of new flame retardant materials: (i) the preparation of a novel flame retardant (FR) additive from bio-resource, (ii) its use as FR additive in poly(lactic acid) (PLA) based composites and, (iii) the in vitro toxicity assessment of the FR. The synthesis of this bio-based FR additive was achieved through a phospha-Michael addition of diphenylphosphine oxide (DPPO) and the naturally occurring compound coumarin, yielding 4-(diphenylphosphoryl)chroman-2-one (CU-DPPO). The flame-retarded CUDPPO PLA composites were prepared either via conventional melt blending of commercially available PLA or through reactive extrusion (REX) of L-lactide. Characterization of the composites was performed through nuclear magnetic resonance (NMR), size exclusion chromatography (SEC) and thermogravimetric analysis (TGA). TGA analysis of the FR-PLA composites showed an increase in thermal stability, confirming the beneficial effect of the CU-DPPO additive. Direct insertion probe mass spectrometry (DIP-MS) analysis was used to gain insight on the mechanism of action of the FR additive, suggesting gas-phase activity. Rheological measurements exhibited the thermo-oxidative stabilizing effect in the modified PLA. The flame retardancy of the melt-blended PLA composites with CU-DPPO was investigated by limited oxygen index (LOI), cone calorimetry and vertical burning tests (UL 94 and BKZ-VB). Samples containing 10 wt.% of CU-DPPO showed improved fire performance with a limiting oxygen index (LOI) of 29 %, passing Swiss vertical burning test (BKZ-VB) and obtaining a V-0 rating in the UL 94 test. Moreover, a preliminary toxicity assessment of the CU-DPPO, carried out using an established in vitro platform, showing no adverse effects on cell viability.