Electrical properties of acrylate grafted polyethylenes

Low density polyethylene (LDPE) was modified by grafting acrylic acid (AA), methylacrylate (MA), ethylacrylate (EA) and n-butylacrylate (NBA), and their electrical properties such as charge distributions, conduction, AC breakdown strength and water tree length were measured. Heterocharge accumulates in LDPE. The heterocharge increases first at low graft ratios, and then decreases at high graft ratios. Homocharge is seen at highly grafted LDPE-g-AA samples. The LDPE shows space-charge-limited conduction mechanism, which remains unchanged at all graft ratios of grafted polyethylenes (GPE). Both AA and NBA reduce the migration of charge effectively, while both MA and EA do not block the migration of charge in GPE. All GPEs except a few samples show higher AC breakdown strength than the LDPE. Water tree length decreases first and then remains unchanged or slightly increases as the graft ratio increases. Both AA and NBA were more effective than both MA and EA in reducing water tree length. This change of electrical properties by graft modification of polyethylene was attributed to the polar groups acting as charge traps.