Abstract: Using a method of direct precipitation, nano magnesium hydroxide (nanoMH) was prepared and modified with oleic acid (OA). The structure and morphology of the nanoMH powders were characterized using contact angle measuring instrument, XRD, TEM, FTIR, and TGDSC．It showed that OA was adsorbed on the surface of nanoMH powders and effectively decreases its surface energies, and hence greatly increased the contact angle. The nanoMH was introduced into PEHD forming a composite through pressing molding. It was found that the limited oxygen index was greatly enhanced by oleic acid treating, the limiting oxygen index increased from 16.8 % to 21.5 % when the nanoMH content was 15 %．

Key words: nano-MH, surface modification, HDPE, flame retardant properties