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.
In this study, two kinds of mineral fillers, bentonite (BNT) and barite (BRT), were incorporated into low density polyethylene (LDPE) by extrusion process. Silane treatment was applied to BRT and BNT surfaces in order to increase their compatibility with LDPE matrix. Surface characteristics of fillers were examined by Fourier transformed infrared spectroscopy (FTIR). LDPE-based composites were prepared at a constant concentration of 10%wt for each additives. Test samples were shaped by injection molding process. Mechanical, thermo-mechanical, water repellency, melt-flow and morphological characterizations of LDPE and its composites were performed by tensile and impact tests, dynamic mechanical analysis (DMA), water absorption test, melt flow index (MFI) measurements and scanning electron microscopy (SEM) technique, respectively. Test results showed that surface treatments led to increase for final properties of composites since they promoted to stronger adhesion between minerals and LDPE matrix compared to untreated ones. Tensile and impact strength values, storage modulus and glass transition temperature of LDPE were improved by inclusion of silane treated minerals. BRT and BNT additions caused no remarkable changes with regard to MFI of LDPE. Additionally, silane modified mineral filled composites exhibited remarkable water resistance behavior. According to SEM analysis of composites, silane treated BNT and BRT containing samples displayed homogeneous dispersions into LDPE phase whereas debondings were observed for untreated BNT and BRT filled composites due to their weak adhesion to polymer matrix.
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