Synergistic Flame Retardant Effects between Aluminum Hydroxide and Halogen-free Flame Retardants in High Density Polyethylene Composites

AbstractThe synergistic flame retardant effects between aluminum hydroxide (ATH) and halogen-free flame retardants in high density polyethylene (HDPE) composites used for geo-grid were characterized by carrying out limited oxygen index (LOI) test, UL94 vertical burn test, alcohol blow 1amp test and cone calorimeter. The fire residue structure of the composites was examined by means of digital camera. The results indicate that there are obvious synergistic flame retardant effects between ATH and the halogen-free flame retardants including expandable graphite (EG) and Red phosphorus (RP). In comparison with ATH/RP system, ATH/EG system has good synergistic effect. Moreover, the synergistic effects of ATH/EG system can act better while further add RP. The LOI of ATH/EG/RP system can rise up to 30.1% and pass alcohol blow lamp test. However, no synergistic flame retardant effect is found between ATH and magnesium hydroxide (MH). Meanwhile, antagonistic effect is existed between ATH and zinc borate (ZnB). The analysis of fire residues show that the formation of char residues of ATH synergistic flame retardant systems act as an effective barrier to reduce the heat release rate and mass loss rate of the composites in condensed phase