Balanced Fire Safety and Mechanical Integrity in Thermoplastic Polyurethane via a Synergistic Ternary System of Hydromagnesite andMicroencapsulated Additives

ABSTRACT To mitigate the trade‐off between flame retardancy and mechanical performance in thermoplastic polyurethane (TPU), an optimized ternary flame‐retardant formulation consisting of hydromagnesite (HM), microencapsulated red phosphorus (MRP), and microencapsulated expandable graphite (MEG) was developed. The thermal stability, fire retardancy, smoke suppression, and mechanical properties of the composites were systematically investigated. At only 12 wt% loading, the optimized composite (TPU/HM1/MEG7/MRP4) achieved an LOI of 39.5% and passed UL‐94 V‐0. Cone calorimetry showed substantial reductions in total heat release (46.3%), peak heat release rate (74.1%), total smoke production (56.7%), and total carbon oxide emissions (61.3%). This superior performance is attributed to a gas–solid dual‐phase synergistic mechanism, involving dilution of combustible volatiles by H 2 O and CO 2 released from HM, possible gas‐phase inhibition by MRP‐derived phosphorus‐containing species, and formation of a compact intumescent char layer driven by MEG expansion and reinforced by MRP‐derived phosphate/polyphosphate‐like species. The optimized composite retained relatively high mechanical ductility, with a tensile strength of 22.1 MPa and an elongation at break of 745%, despite a reduction compared with pristine TPU. This work provides an effective low‐loading formulation‐optimization strategy for improving TPU fire safety while maintaining acceptable mechanical flexibility.