Univ. Lille, ENSCL, UMR 8207-UMET-Unité Matériaux et Transformations , F-59652 Villeneuve d'Ascq , France.
Univ. Lille, CNRS, UMR 8516-LASIR-Laboratoire de Spectrochimie Infrarouge et Raman , F-59652 Villeneuve d'Ascq Cedex , France.
ACS Appl Mater Interfaces. 2018 Jul 25;10(29):24860-24875. doi: 10.1021/acsami.8b07323. Epub 2018 Jul 16.
The contribution of copper complexes of salen-based Schiff bases N, N'-bis(salicylidene)ethylenediamine (C1), N, N'-bis(4-hydroxysalicylidene)ethylenediamine (C2), and N, N'-bis(5-hydroxysalicylidene)ethylenediamine (C3) to the flame retardancy of thermoplastic polyurethane (TPU) is investigated in the context of minimizing the inherent flammability of TPU. Thermal and fire properties of TPU are evaluated. It is observed that fire performances vary depending upon the substitution of the salen framework. Cone calorimetry [mass loss calorimetry (MLC)] results show that, in TPU at 10 wt % loading, C2 and C3 reduce the peak of heat release rate by 46 and 50%, respectively. At high temperature, these copper complexes undergo polycondensation leading to resorcinol-type resin in the condensed phase and thus acting as intumescence reinforcing agents. C3 in TPU is particularly interesting because it delays significantly the time to ignition (MLC experiment). In addition, pyrolysis combustion flow calorimetry shows reduction in the heat release rate curve, suggesting its involvement in gas-phase action. Structural changes of copper complexes and radical formation during thermal treatment as well as their influence on fire retardancy of TPU in the condensed phase are investigated by spectroscopic studies supported by microscopic and powder diffraction studies. Electron paramagnetic resonance (EPR) spectroscopy was fully used to follow the redox changes of Cu(II) ions as well as radical formation of copper complexes/TPU formulations in their degradation pathways. Pulsed EPR technique of hyperfine sublevel correlation spectroscopy reveals evolution of the local surrounding of copper and radicals with a strong contribution of nitrogen fragments in the degradation products. Further, the spin state of radicals was investigated by the two-dimensional technique of phase-inverted echo-amplitude detected nutation experiment. Two different radicals were detected, that is, one monocarbon radical and an oxygen biradical. Thus, the EPR study permits to deeply investigate the mode of action of copper salen complexes in TPU.
研究了以 N, N'-双（水杨醛）乙二胺（C1）、N, N'-双（4-羟基水杨醛）乙二胺（C2）和 N, N'-双（5-羟基水杨醛）乙二胺（C3）为配体的水杨醛希夫碱铜配合物对热塑性聚氨酯（TPU）阻燃性的贡献，目的是降低 TPU 的固有可燃性。评估了 TPU 的热性能和燃烧性能。观察到，取代水杨醛骨架会改变燃烧性能。锥形量热仪[质量损失量热仪（MLC）]结果表明，在 TPU 中，C2 和 C3 的添加量为 10wt%时，分别将放热量峰值降低了 46%和 50%。在高温下，这些铜配合物会发生缩聚反应，在凝聚相中生成间苯二酚型树脂，从而起到膨胀增强剂的作用。在 TPU 中，C3 特别有趣，因为它显著延迟了点火时间（MLC 实验）。此外，热解燃烧流热量计表明，热释放率曲线降低，表明其参与了气相作用。通过光谱研究，结合微观和粉末衍射研究，研究了铜配合物的结构变化和自由基形成以及它们在凝聚相中对 TPU 阻燃性的影响。电子顺磁共振（EPR）光谱被充分用于跟踪 Cu(II)离子的氧化还原变化以及铜配合物/TPU 配方在降解途径中的自由基形成。超精细亚层相关光谱的脉冲 EPR 技术揭示了铜和自由基的局部环境随降解产物中氮片段的强烈贡献而演变。此外，通过二维相位反转回波幅度检测进动实验技术研究了自由基的自旋态。检测到两种不同的自由基，即一种单碳自由基和一种氧双自由基。因此，EPR 研究可以深入研究铜水杨醛配合物在 TPU 中的作用模式。
