Space charge behavior of acrylic monomer-grafted polyethylene

This report describes space charge behavior of polyethylene (PE) grafted with acrylic monomers such as acrylic acid (AA), methacrylate (MA), ethylacrylate (EA) and n-butyl acrylate (NBA). The specimens were 0.7 mm thick with semicon electrodes, and vacuum degassed. Heterocharge is found in ungrafted control PE. This heterocharge decreases with the increase of AA content when AA is grafted onto the PE chains. This was attributed to an enhanced charge trapping at carbonyl sites provided by AA. When other acrylic monomers are grafted, heterocharge of the control PE increases first at low graft ratios and then decreases at higher graft ratios. This change was attributed to the combined effects of alkoxy groups acting as electron donating species and carbonyls acting as charge trapping sites. It seems that charge trapping at the carbonyls is sacrificed in part by the alkoxy groups at low graft ratios. All grafted polyethylenes are found at low fields below 1×10⁵ V/cm to obey the space-charge limited conduction (SCLC) mechanism. Effective charge mobilities of PE-g-AA and PE-g-NBA decrease with the increase of graft ratio while those of others remain unchanged