Mechanochemical Interfacial Engineering for Flame-Retardant Thermoplastic Polyurethane Composites

Flame-retardant thermoplastic polyurethane (TPU) composites are essential for improving fire safety across a range of industrial applications. However, conventional strategies involving phosphorus- and nitrogen-based flame retardants often require high additive loadings, which significantly compromise the mechanical properties of the resulting composites. While most existing methods depend on solvent-based processes, this study introduces an all-dry mechanochemical (MC) process to fabricate TPU composites that simultaneously achieve high flame retardancy and mechanical robustness. The MC process was conducted in two stages: first, to functionalize the surface of aluminum diethylphosphinate (AlPi) with melamine cyanurate (MCA), yielding a hybrid flame retardant (MCAlPi), and second, to promote physical adhesion between MCAlPi and TPU particles, thereby improving interfacial compatibility. Microstructural analyses confirm the uniform dispersion of MCAlPi within the TPU matrix, in contrast to the aggregation observed in composites prepared without MC treatment. The MC-processed composites achieve a UL-94 V-0 rating with a 6 wt % reduction in flame retardant loading and exhibit a 64% improvement in tensile strength relative to untreated counterparts. These results demonstrate that the solvent-free MC strategy not only matches or surpasses the performance of conventional solvent-based methods but also offers a cost-effective, scalable, and environmentally sustainable route for producing flame-retardant polymer composites with a well-balanced combination of fire resistance and mechanical performance.