Novel Ultrathin Layered Double Hydroxide Nanosheets with In Situ Formed Oxidized Phosphorus as Anions for Simultaneous Fire Resistance and Mechanical Enhancement of Thermoplastic Polyurethane AITranslate

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DOI：https://doi.org/10.1021/acsapm.9b00203

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Thermoplastic polyurethane (TPU) is widely used in wires, cables, etc., facing a big challenge in its fire safety under many cases. Traditional nanoparticles with a flame-retardant feature are showing an application prospect in preparing flame-retarding TPU with excellent overall performance because of their unique structural characteristic. However, almost all of these nanoparticles are not highly efficient in fabricating flame-retarding polymers. In this work, we developed novel ultrathin layered double hydroxide nanosheets with in situ formed oxidized phosphorus as anions (P-LDH) via a simple and versatile ball-milling method to prepare flame-retarding TPU. Compared with nanoparticles which were used in TPU before, the P-LDH showed an obvious advantage in simultaneously enhancing and flame-retarding TPU. At only 5.0 wt % of P-LDH, TPU/P-LDH achieved a UL-94 V-0 rating and a limiting oxygen index of 28.0% during burning tests, obviously superior to a UL-94 V-2 rating and a limiting oxygen index of 23.0% for pure TPU; its total heat release was decreased by 70.9% compared with that of pure TPU in the cone calorimeter test. Meanwhile, both tensile strength and elongation at break of TPU were increased by 9.3 and 6.2% in comparison with the corresponding values of pure TPU at 5.0 wt % of P-LDH. A study on the fire resistance mechanism revealed that the structural change of char residue dominated the improved flame retardance of TPU/P-LDH. For the effect of P-LDH on mechanical properties of TPU, the improved dispersity of ultrathin P-LDH nanosheets played a leading role. All of these experimental results demonstrated that mechanochemical reaction-induced anion substitution and high exfoliation for LDH nanosheets is an efficient method for preparing TPU with simultaneous flame retardance and excellent mechanical properties.