Abstract: Inorganic fillers are widely used in polyolefin modification in order to improve the strength and toughness,and cut down the cost as well.However, the effects of the fillers and the coupling agents on the photo-oxidation degradation of polyolefins were not studied throughly.The natural photo-oxidation degradations of HDPE(high density polyethylene)-CaCO₃ composites were studied.The results show that the mass concentration of CaCO₃ doesn't influence the oxidation degree of HDPE much,while the hydroxyl index of HDPE composite increases with the concentration of CaCO₃.The coupling agents play different roles in the photo-oxidation degradation of HDPE-titanate can accelerate the oxidation of HDPE greatly,while other coupling agents have minor influences. In the samples with the thickness of about 3.2 mm,the depth profiles were investigated by infrared microscopy,and the section morphologies were observed as well.The crack length in the section of HDPE-CaCO₃-titanate composite corresponds exactly to the transition point in the corresponding CI vs. depth curve.The addition of CaCO₃ and its surface treatment with different coupling agents lower the crystallinities of HDPE greatly.From these demonstrations,a hypothesis may be proposed that the lower crystallinity of a composite permits the oxygen to diffuse further into the interior and supplies more surface areas for the oxidation reaction to occur,and,thus,results in the higher oxidation degree.

Key words: HDPE-CaCO₃ composite, Photo-oxidation, Infrared microscopy