Abstract: In this work, a flame retardant high density polyethylene (PE-HD) composite containing microencapsulated red phosphorus (MRP), magnesium hydroxide (MH), and expandable graphite (EG) was prepared via melt extrusion, which was characterized using LOI, UL 94, FT-IR, Raman, TG?DTA, SEM, and tensile testing. The possible flame retardant mechanism in the composites was proposed. It was found that EG alone possessed poor efficiency in flame retarding. However, when combined with MRP and MH, the flame retardancy was obviously emhanced. When PE-HD/ MH /MRP /EG = 100/35/15/5 in mass, the limited oxygen index of the composite was 28.5 %, vertical firing ranked UL 94 V-0. SEM showed that PE-HD was compatible with EG, but not with MRP and MH.

Key words: Microencapsulated red phosphorus, Magnesium hydroxide, Expandable graphite, High density polyethylene, Flame retardant