Synthesis of anhydrous manganese hypophosphite microtubes for simultaneous flame retardant and mechanical enhancement on poly(lactic acid)

In this study, a facile solvothermal approach for preparing anhydrous manganese hypophosphite (A-MnHP) microtubes was demonstrated for the first time by using manganese chloride and hypophosphorous acid in mixed solvents, followed by fabricating A-MnHP-based poly(lactic acid) (PLA) composites via a melt-blending method. Owing to the unique morphology of A-MnHP, the tensile strengths of the PLA composites with 1 wt%, 5 wt% and 10 wt% A-MnHP are approximately 17%, 7% and 3% higher than those of neat PLA, respectively. Compared to neat PLA, PLA composite containing 15 wt% A-MnHP (PLA/A-MnHP15) exhibited lower peak heat release rate (50% reduction), total heat release (13% reduction), peak CO₂ and CO productions (50% and 53% reductions), which also passed UL 94 V-2 rating test with high limiting oxygen index (27.5%). The combustion temperature change during the cone calorimeter tests showed that PLA/A-MnHP15 showed the lowest combustion temperature, achieving the best fire safety performance. Residue analysis indicated that the presence of A-MnHP resulted in the formation of continuous and compact char residues composed of aromatic structure and phosphorous-rich inorganic structure, retarding the permeation of heat, oxygen transfer and escape of volatile degradation products.

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