ABSTRACT Polylactic acid (PLA) is highly flammable and prone to severe melt dripping during combustion, which severely restricts its application in fire‐sensitive fields. In this study, a novel flame‐retardant PLA composite was successfully developed to overcome the traditional trade‐off among flame retardancy, anti‐dripping, and mechanical performance. A phosphorus‐containing polyurethane crosslinked network (MTD) was constructed in situ via reactive melt blending of 4,4‐methylenebis (phenyl isocyanate) (MDI), tris(2‐hydroxyethyl) isocyanurate (THEIC), and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO‐HQ), and combined with ammonium polyphosphate (APP). The optimized formulation, PLA/MTD20/A10 (20 wt% MTD and 10 wt% APP), achieved a UL‐94 V‐0 rating with no melt dripping and a limiting oxygen index (LOI) of 25.5%. Cone calorimetry results demonstrated a 40.2% reduction in the peak heat release rate (pHRR). The excellent anti‐dripping performance is attributed to the in situ constructed P–N–C crosslinked network, which significantly improved the high‐temperature storage modulus from 17.6 to 182.3 MPa, effectively avoiding melt flow. Furthermore, the composite exhibited exceptional mechanical property retention, maintaining 93.6% of its tensile strength and improving elongation at break by 27.3%. The dual‐mode flame‐retardant mechanism relies on the synergy between gas‐phase radical quenching by PO· subspecies and the formation of a dense, honeycomb‐like graphitized char layer in the condensed phase. This reactive crosslinking strategy expands the potential applications of PLA in industries requiring high fire safety.
Chen et al. (Mon,) studied this question.
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