Metallic phytates as efficient bio-based phosphorous flame retardant additives for poly(lactic acid)

In this study, we evaluated the potential flame retardant effect of different metallic phytates as biosourced phosphorous additives for poly(lactic acid) (PLA). Starting from sodium phytate, the sodium cations were replaced by aluminum, iron or lanthanum cations as attested by elemental analysis. PLA-metallic phytate composites containing 20 or 30 wt% of additives were produced by melt blending in an internal mixer and their fire properties, thermogravimetric resistance have been characterized as well as the PLA chain degradation occurring during melt processing. The most significant flame retardant effect, observed by cone calorimeter test, was obtained when aluminum phytate was used. Cone calorimeter testing combined with pyrolysis combustion flow calorimetry (PCFC) analysis indicated that the barrier effect was more significant in the case of PLA filled with aluminum phytate. However, aluminum phytate proved to be responsible for PLA chain degradation during melt processing. Combinations of metallic phytate and native sodium phytate overcame this negative effect and allowed for limiting the thermal degradation of PLA during melt processing while preserving good fire performances, i.e. significant pHRR reduction and V-2 classification in UL-94 test.