Abstract: the flame retardant properties of PE based composite with Ca(OH)2 and Mg(OH)2 were characterized with oxygen index analyzer, vertical horizontal analyzer, SEM, and TG. When the totalcontent of Ca(OH)2 and Mg(OH)2 was 35 wt%，the LOI of the composite reached 24.5%，and the Tmax lagged neat PE by 9.2℃ .The formation of dense char layer was promoted.Ca(OH)2 and Mg(OH)2 had some synergistic effects to the flame retardant properties of PE. It could be expected to replace some of Mg(OH)2 with low cost Ca(OH)2.

Key words: calcium hydroxide, magnesium hydroxide, polyethylene, flame retardancy, synergistic effect