Effect of Alumina Trihydrate and Borax on Fire Retardancy and Mechanical Properties of High Density Polyethylene (Hdpe) Compounds

The influence of the inorganic flame retardants, including alumina trihydrate (ATH) and borax (Na ₂ B ₄ O ₇ -10H ₂ O, hydrated sodium tetraborate), on the mechanical properties and flammability of high density polyethylene has been studied. Results showed that an increase in the amount of flame retardant compounds caused a decrease in tensile strength, ultimate strain and impact resistance. Using of ethylene vinyl acetate (EVA) caused an increase in impact resistance compared to other compositions without EVA. Flammability test results showed an improvement in flame retardancy due to using alumina trihydrate and borax. Composite containing EVA and borax showed better flammability properties compared with composite containing EVA and ATH because, EVA as a compatibiliser can increase the stability of the borate component and form a glassy layer on the char, which results in an enhancement in the flammability properties. Furthermore a synergistic effect was observed when alumina trihydrate and borax were incorporated together. The charred layers provided a good thermal and flame barrier. Morphological, rheological and thermal gravimetric analyses studies supported the idea that the improvement in the flame retardancy was due to charred layers formed by the ignition of inorganic flame retardant and polymeric matrix.