Abstract
The polycyclic aromatic compounds were added to low density polyethylene (LDPE) with the concentration of 0.1-1.6wt% to restrict the generation of electrical tree in LDPE. 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 are in the range from 0.5wt% to 0.75wt%, the tree inception voltage for LDPE/An is 3.5-4 times higher than that for LDPE 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 has much less effect for the increase in the inception voltage than that of An, and the inception voltage for LDPE/Nf is almost the same as that for LDPE 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 LDPE/An and surface roughness on LDPE/An is almost 0.17times smaller than that on the other materials. The roughness of the other samples is not small as that of LDPE/An. It is estimated that free volume at an interface between electrode and polymer for LDPE/An is smaller than that for LDPE without additive. It is considered that the increase in the inception voltage for LDPE/An results mainly from the small size of free volume at the interface.
