Use of boron compounds as synergistic flame retardant in low density polyethylene – ethylene vinyl acetate blends and nanocomposites

İbibikcan, Esin
It is known that for the production of halogen-free cable insulation materials based on polyethylene, very high amounts of traditional metal hydroxide flame retardants such as 65 wt% aluminum hydroxide (ATH) is required to fulfill international directives. Thus, flammability studies investigating synergistic compounds and contribution of nanomaterials have been crucial. Therefore, the first purpose of this thesis was to reveal possible synergism of three boron compounds zinc borate (ZB), boron oxide (BO) and boric acid (BA) on the flame retardancy of two cable insulation materials; low density polyethylene (LDPE) and its blend with ethylene vinyl acetate (EVA) both loaded with ATH. The second purpose of this thesis was to investigate contribution of nanoclays when used alone, and together with ATH, and also together with ATH-ZB synergistic system. For these purposes, materials were compounded by melt mixing method with a laboratory scale twin-screw extruder, while specimens were shaped by compression and injection molding. Flammability properties of the specimens were investigated by using Limiting Oxygen Index (LOI), UL-94 Vertical Burning and Mass Loss Cone Calorimeter (MLC) analyses. Other characterization techniques required in this thesis were; X-ray diffraction analysis (XRD), scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA) and tensile tests. Flammability tests in the first part of this study simply revealed that replacement of certain amount of ATH with boron compounds could lead to certain levels of synergism in many flame retardancy parameters. Residue analyses revealed that these improvements were basically due to further contribution of boron compounds to the physical barrier mechanism of ATH in both gas and condensed phases. Analyses in the second part of this study indicated that even use of nanoclays alone could improve many flammability parameters including peak heat release rate, time to ignition and fire growth index. Contributions of nanoclays were much more significant when they were incorporated together with traditional ATH or together with synergistic ATH-ZB system. Residue analysis revealed that contribution of nanoclays to the flame retardancy mechanisms of ATH and ZB was mainly by formation of strong and tough char structure via well-dispersed and intercalated/exfoliated silicate layers shielding the underlying polymer matrices from heat and mass transfer.
Citation Formats
E. İbibikcan, “Use of boron compounds as synergistic flame retardant in low density polyethylene – ethylene vinyl acetate blends and nanocomposites,” M.S. - Master of Science, Middle East Technical University, 2013.