Abstract
Novel polymeric acrylate-based flame retardants (FR 1–4) containing two phosphorus groups in different chemical environments were synthesized in three steps and characterized via nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS). Polylactic acid (PLA) formulations with the synthesized compounds were investigated to evaluate the efficiency of these flame retardants and their mode of action by using TGA, UL94, and cone calorimetry. In order to compare the results a flame retardant polyester containing only one phosphorus group (ItaP) was also investigated in PLA regarding its flame inhibiting effect. Since the fire behavior depends not only on the mode of action of the flame retardants but also strongly on physical phenomena like melt dripping, the flame retardants were also incorporated into PLA with higher viscosity. In the UL94 vertical burning test setup, 10% of the novel flame retardants (FR 1–4) is sufficient to reach a V-0 rating in both PLA types, while a loading of 15% of ItaP is not enough to reach the same classification. Despite their different structure, TGA and cone calorimetry results confirmed a gas phase mechanism mainly responsible for the highly efficient flame retardancy for all compounds. Finally, cone calorimetry tests of the flame retardant PLA with two heat fluxes showed different flame inhibiting efficiencies for different fire scenarios.
Highlights
Due to oil scarcity and environmental issues, green alternatives of petrochemical products have gained a lot of impact in recent years. [1,2] One promising candidate for replacing traditional fossil-based polymer materials is poly (PLA)
[15] Senlong et al reported that the flame retardant performance of Polylactic acid (PLA) composites is enhanced by melt blending of neat PLA with DOPO containing PLA (P-PLA), which was synthesized by chain extension of L-Lactide with a DOPO derivative
Further research groups incorporated and investigated other DOPO derivatives in PLA, such as a DOPO-montmorillonite based compound, a DOPO-modified Co-based metal-organic framework (MOF) and a DOPO containing silesquioxane. [17,18,19] Besides these petrochemical flame retardants efforts were made to produce greener alternatives for flame retardant PLA involving the incorporation of biomass derived charring agents or flame retardants derived from biobased chemicals like pentaerythritol
Summary
Due to oil scarcity and environmental issues, green alternatives of petrochemical products have gained a lot of impact in recent years. [1,2] One promising candidate for replacing traditional fossil-based polymer materials is poly (lactic acid) (PLA). [1,2] One promising candidate for replacing traditional fossil-based polymer materials is poly (lactic acid) (PLA) It is derived from renewable resources, and biodegradable. Polymers 2020, 12, 778 compounds, and mineral fillers were incorporated and their effect on flame retardancy of PLA was investigated. [15] Senlong et al reported that the flame retardant performance of PLA composites is enhanced by melt blending of neat PLA with DOPO containing PLA (P-PLA), which was synthesized by chain extension of L-Lactide with a DOPO derivative. Further research groups incorporated and investigated other DOPO derivatives in PLA, such as a DOPO-montmorillonite based compound, a DOPO-modified Co-based metal-organic framework (MOF) and a DOPO containing silesquioxane. The PLA composites achieved a UL94 V-0 rating upon addition of 20–30 wt.% of one of these biomass derived compounds. The incorporation of the new compounds in PLA improved the flame retardancy, reaching a V-0 classification with 20 wt.%
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