Preparation of cobalt-based metal organic framework and its application as synergistic flame retardant in thermoplastic polyurethane (TPU)

Firstly cobalt-based metal-organic framework material (Co-MOF) was designed and synthesized; its composition was studied by fourier transform infrared spectroscopy (FTIR) and energy dispersion spectrum (EDS), and the micrographs were observed by scanning electron microscope (SEM). Several burning test results showed that the flame retardant of TPU was obviously improved by the help of combination of 4.5 wt% APP/1.5 wt% Co-MOF. TPU is easily flammable with severe molten drops, so its limited oxygen index (LOI) is only 21.7 and cannot pass any UL-94 grade in vertical burning test. Whereas in TPU/6.0 wt% (4.5APP/1.5Co-MOF) composites, LOI raised to 28.2 and no dripping was produced in vertical burning test, so it passed UL-94 V-0 grade. Similarly, TPU released a large amount of heat and smoke in cone test, peak heat release rate (pHRR) reached 1359 kW m−2 and smoke production rate (SPR) was 0.11 m−2 s−1; however, in TPU/6.0 wt% (4.5APP/1.5Co-MOF) composites, pHRR reduced sharply to 257 kW m−2 and SPR dropped to 0.04 m−2 s−1. Most of all, some mechanical loss caused by the APP were partly recovered by substitutional use of Co-MOF.