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From viewpoints of environmental protection and reduction in manufacturing cost, it is desirable to use non-crosslinked polyethylene as an insulating material for power cables. A new type polymerized polyethylene using a single-site catalyst has an advantage of its high melting point, but its processability is very poor because of its high viscosity. Therefore, blends of this polyethylene and conventional low-density polyethylene with different blending ratios are examined in this research. As a result, it has become clear that the blend with a blending ratio of 1:1 has an appropriate melting stress and an adequate viscosity at a shear velocity suitable for cable manufacturing. Furthermore, the blend has a superior thermal property and a high dielectric strength for both dc and impulse voltages.

The relation between morphological change, induced by copolymerized benzene rings or by kneading, and the dielectric strength of ethylene-styrene copolymer was studied. In unkneaded samples, the lamellar thickness decreases and the lattice constant along the a-axis increases with increasing styrene content. However, in kneaded samples, the lamellar thickness and the lattice constant remain constant up to a styrene content of 3.10 wt.%. Spherulite is observed with a polarizing microscope in unkneaded samples, but it disappears in kneaded samples. Kneaded samples, especially the kneaded sample with a styrene content of 3.10 wt.%, have higher breakdown strength than unkneaded samples. The styrene content of the sample showing the highest breakdown strength increases as the temperature decreases. At -50 degrees C or -80 degrees C, the sample with a styrene content of 15.40 wt.% has the highest breakdown strength of all the samples. It is considered that benzene rings are moved to the interfacial region between lamellar and amorphous parts by kneading and hinder the acceleration of electrons along the lamellae. This effect of benzene rings becomes pronounced in the low-temperature region where the breakdown process is electronic. >