红外光谱法研究成核剂对聚丙烯光氧化降解的影响

采用红外光谱和显微红外光谱，对添加两种α成核剂(TM-1、TM-3)和一种β成核剂(TMB-5)的聚丙烯(PP)的自然光氧化降解行为及机理进行了研究。结果表明，添加成核剂前后，PP的光氧化降解产物均含有酮、羧酸、酯、醇和不饱和烃等。三种成核剂的加入并没有改变PP的光氧化降解机理和降解产物，但都对PP的光氧化反应起了一定的加速作用。各体系的光氧化速率依次为：PP/TMB-5>PP/TM-3>PP/TM-1>PP。PP与添加成核剂的PP中的光氧化程度沿深度的分布表现出相似的规律：表面处的羰基指数最高，自曝晒表面向内部，羰基指数逐渐降低，到约250 μm处减小到约为0，这个范围称之为表面氧化层。表面氧化层的厚度不随曝晒时间的不同而不同，而是由紫外光的穿透能力、氧气的扩散、尤其是加工时样品中的温度梯度所决定的。

Study on the Effects of Nucleating Agents on Photooxidation Degradation of PP by FTIR and IM

In the present paper, the natural photooxidation degradation behavior and mechanism of PP containing two α-nucleating agents (TM-1 and TM-3) and a β-nucleating agent (TMB-5) were studied by Fourier transform infrared spectroscopy (FTIR) and infrared microscopy (IM) so that helpful instructions would be obtained for the PP material design and applications. The results showed that the nucleating agents had significant impact on the photooxidation stability of PP. The existence of them accelerated the photooxidation reaction of PP to different extents with the rank of PP/TMB-5＞PP/TM-3＞PP/TM-1＞PP. However, the photooxidation procedure and the corresponding oxidative products did not change. The oxidation profiles in PP and nucleated PP bars after exposure had similar trends. The carbonyl index curves had a maximum at the surface and declined gradually with distance from the exposed surface, then decreased to nearly zero at the depth of about 250 μm, which was named as the surface oxidation layer (SOL). The SOL thickness, which was dependent on the transmission of the ultraviolet light, the oxygen diffusion and mostly the “skin” layer formed during the injection moulding, did not change with exposure time. The development of oxidation along the depth coincided with the initiation and propagation of the surface cracks. Before fragments dropped from the seriously oxidized surface, the photooxidation degradation of PP was restricted mainly in the surface oxidation layer.