Flame-retardant features of various boron compounds in thermoplastic polyurethane and performance comparison with aluminum trihydroxide and magnesium hydroxide

The objective of this research was to examine and compare the flame-retardant properties of boron compounds with respect to conventional mineral fillers, namely aluminum trihydroxide (ATH) and magnesium hydroxide (MH) in thermoplastic polyurethane (TPU). Seven different boron compounds including zinc borate (ZnB), colemanite (C), boron oxide (BO), anhydrous borax (BX), melamine borate (MB), imidazolium borate (IB), and guanidinium borate (GB) were used as flame-retardant additive. The flame-retardant characteristics of the composites were investigated using limiting oxygen index (LOI), vertical and horizontal UL-94 tests, and mass loss calorimeter (MLC) tests. According to the flammability test results, the highest LOI value (33.5%) was obtained with the use of 60 wt% ATH and BO. All samples got HB rating in UL-94 HB test. The highest UL-94 V rating of V0 was achieved with the use of ATH (60 wt%), BO (60 wt%), and GB (50 wt%). According to MLC test results, C, BO, and IB showed distinct better performance than ATH and MH. The other ones showed almost the similar fire performances. The lowest pHRR (37 kW/m(2)) and THE (16.2 MJ/m(2)) values, which were corresponded to 62% and 20% reduction with respect to those of ATH containing one, were achieved with the use of 60 wt% BO. In brief, all studied additives exerted different levels of fire retardancy depending upon their type and BO showed the highest performance in terms of flammability and fire-retardant properties