Effects of Aluminium Tri-hydroxide and Zinc Borate on the Flame Retardancy and Mechanical Properties of Recycled High-Density Polyethylene

This work aimed to investigate the effects of aluminum tri-hydroxide (ATH) and zinc borate (ZB) on the flame retardant and mechanical properties of recycled high-density polyethylene (rHDPE). The flame retardants were added at concentrations of 0, 30, 60, 90, and 120 parts per hundred (pph). Tests were conducted following UL-94 standards, the limiting oxygen index (LOI), tensile properties, and the melt flow index (MFI). The results showed that incorporating ATH into rHDPE at concentrations of 90 and 120 pph achieved a flame-retardant rating of V-0, with an LOI value between 23 and 24, classifying it as a non-flammable material. Additionally, adding ZB at a concentration of 120 pph resulted in a flame-retardant rating of V-2. The addition of both flame retardants did not affect the tensile modulus or tensile strength. However, elongation at break and tensile toughness decreased. Furthermore, the melt flow index (MFI) tended to decrease with increasing amounts of additives. Therefore, based on the experimental results, rHDPE with 90 pph of ATH is the recommended formulation, offering both excellent flame retardancy and tensile strength properties.