显微红外光谱法研究聚丙烯纳米复合材料的光氧化降解

采用显微红外(AIM)光谱法，结合偏光显微镜(POM)和扫描电子显微镜(SEM)，对聚丙烯/碳酸钙(PP/CaCO₃)和聚丙烯/二氧化硅(PP/SiO₂)纳米复合材料中光氧化降解沿深度的分布进行了研究。结果表明，无论是纯聚丙烯还是聚丙烯纳米复合材料，试样的光氧化降解都是氧扩散控制过程，由表面逐渐向内部发展。纳米碳酸钙和纳米二氧化硅的加入都显著地促进了PP基体的光氧化降解，二氧化硅的影响更为严重。纳米填料的含量越高，复合材料的氧化程度也越高，但氧化层的厚度却基本不变，都在200 μm左右，当样品表面严重老化至表面脱落后，氧化继续向内部进行。氧化层的厚度主要是由试样成型过程中形成的表面过渡区的厚度决定的。

Study on Natural Photo-Oxidation Degradation of Polypropylene Nanocomposites by Infrared Microscopy

Polymer nanocomposites have attracted great attention because of the demand for polymer materials with high performance and high functionality at the same time.Nano CaCO₃ and SiO₂ can be used to improve the rigidity of polypropylene (PP), which is quite importance for biaxial orientation PP film.However, the effect of these nano fillers on natural photo-oxidation degradation of PP has not been studied.In the present paper, the natural photo-oxidation profiles along the depth of PP and PP nanocomposites bars were studied with infrared microscope (IM) as well as polarizing lighu microscope (PLM) and scanning electron microscope (SEM).The results indicated that nano CaCO₃ and SiO₂, especially the latter, accelerated the oxidation rate of PP significantly, with more and deeper surface cracks.Larger amount of nano filler gave rise to greater oxidation degradation. The existence of nano CaCO₃ and SiO₂ helped to diminish the spherulite and broaden the transition region from amorphous to crystal.The oxidation development along the depth in PP nanocomposites depended on the diffusion rate of oxygen and underwent two stages.In the first stage, the oxidation degree increased with time because of the low density in the transition region.In the layer under this region, the oxidation is difficult to occur owing to the high density of crystals and oxygen starvation.Therefore, the oxidation depth profiles decreased to near zero at nearly the same depth - about 200 μm from the exposed surface, corresponding to the transition region in PLM observation, namely surface oxidation layer.The high degree of oxidation in the surface layer gave rise to crack formation, and these surface cracks helped further oxidation in PP nanocomposites.In the second stage, the interconnection of surface cracks resulted in the fracture of the seriously oxidized surface oxidation layer.Consequently, the oxidation of the subsurface layer began and the depth profile developed to deeper place.In PP, the much thinner surface amorphous layer and the relatively perfect crystallization under it were responsible for the higher stability during the natural exposure.