Control of Electrical Tree generation in Low Density Polyethylene by Addition of Polycyclic Aromatic Compound.

在低密度聚乙烯(PE)中加入浓度为0.1~1.6wt%的多环芳香族化合物，以限制PE中电树的产生。所用化合物为萘(Nf)、菲(AN)、四苯(Te)、并五苯(Pn)和9，10溴菲(BrO-AN)。在插入含有添加剂的PE块的针状电极上施加交流(50赫兹)高压。实验结果表明，当添加剂浓度在0.5wt%~0.75wt%范围内时，PE/AN的树枝起始电压是不加添加剂的PE的3.5~4倍。然而，AN的加入并不能限制在试件中产生的树的繁殖。添加其他添加剂对起始电压的影响远小于AN，而PE/NF的起始电压与未加入添加剂的PE几乎相同。结合紫外吸收光谱、DSC和SPM的实验结果，讨论了AN提高树枝起始电压的机理。扫描电子显微镜观察表明，只在PE/AN的表面形成高密度的纤维状结构，其表面粗糙度几乎是其他材料的0.17倍。其他样品的粗糙度并不比PE/AN的小。PE/AN的导电电流和tanδ均小于未添加添加剂的PE等其他材料。据估计，PE/AN与电极界面的自由体积尺寸小于未加添加剂的PE。认为PE/AN起始电压的提高主要是由于界面自由体积较小所致。

The polycyclic aromatic compounds were added to LDPE (PE) with the concentration of 0.1-1.6wt% to restrict the generation of electrical tree in PE. The compounds used were naphthalene(Nf), anthracene(An), tetracene(Te), pentacene(Pn) and 9,10 bromo-anthracene(Br-An). AC(50Hz) high voltage was applied to a needle electrode inserted to a block of PE with the additive. The experimental results show that when the concentrations of additive range from 0.5wt% to 0.75wt%, the tree inception voltage for PE/An is 3.5-4 times higher than that for PE without additive. However, the addition of An is not able to restrict the propagation of tree generated in the specimen. The addition of the other additives except for Nf have much less effect for the increase in the inception voltage than that of An, and the inception voltage for PE/Nf is almost the same as that for PE without additive. The mechanisms for increasing the tree inception voltage by An were discussed refereeing to our experimental results with UV absorption spectrum, DSC and SPM. SPM observation revealed that high density fibrous construction is formed only on the surface of PE/An and surface roughness on PE/An is almost 0.17 times smaller than that on the other materials. The roughness of the other sample is not small as that of PE/An. Conductive current and tanδ for PE/An are smaller than those for the other materials including PE without additive. It is estimated that a size of free volume for PE/An at an interface with electrode is smaller than that for PE without additive. It is considered that the increase in the inception voltage for PE/An results mainly from the small size of free volume at the interface.