聚乙烯-碳酸钙复合材料的光氧化降解及沿深度的分布

研究了聚乙烯-碳酸钙复合材料薄膜和厚试样的自然光氧化降解.结果表明,碳酸钙含量对复合材料的氧化程度影响不大,但羟基指数随碳酸钙含量增大而增大.不同的表面处理对复合材料的氧化降解影响很大,用钛酸酯进行表面处理,可大大促进聚乙烯的氧化降解,其它的偶联剂则没有明显的影响.用显微红外研究厚试样中氧化程度随深度的变化,发现从表面到中心,不同体系的羰基指数表现出不同程度的衰减,断面呈不同的老化形貌.含钛酸酯的体系,羰基指数沿深度方向明显下降,曲线的转折点与断面上的裂纹深度相对应.填充碳酸钙以及碳酸钙的表面处理会明显降低聚乙烯的结晶度.结合氧化程度分布、裂纹以及结晶度对复合材料的光氧化机理进行了讨论.

Photo-oxidation Degradation and Depth Profiles of Polyethylene-CaCO3 Composites

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.