Effects of Acetophenone on Charge Dynamics in Low Density Polyethylene

It is well-known that space charge accumulates easily in polyethylene in the presence of crosslinking byproducts. Acetophenone is one of the mainly byproducts produced after crosslinking with dicumyl peroxide (DCP). This paper intended to investigate the mechanism of space charge formation with the existence of acetophenone in polyethylene. The addictive-free low density polyethylene (LDPE) sheets and the LDPE soaked into acetophenone for 24 hours (referred as L-AP) with $\mathbf{300}\mu\mathbf{m}$ thickness were prepared. The space charge distribution and high field conduction characteristics were measured in both untreated LDPE (referred as L-u) and L-AP. In the space charge measurement using pulsed electroacoustic (PEA) technique, three relatively low DC electric fields, 5, 7, and 10 kV/mm were applied subsequently at 298 K and 323 K. It is generally acknowledged that no obvious space charge can be observed under these fields in LDPE. In the high field conduction measurement, samples were stressed under DC electric field at the same temperature. Gas chromatography-mass spectrometry (GC-MS) was employed before and after space charge test to investigate the variation of acetophenone. According to the space charge distribution in L-AP, negative charges started to appear under 5 kV/ mm in the vicinity of the anode at 298 K and positive charges dominated the bulk of the sample at 323 K. The acetophenone content decreased during the space charge test from GC-MS result. Acetophenone changed the pattern of space charge in LDPE, which became more obvious at high temperature. According to the conduction measurement results, the dissociation of acetophenone brought about more free charges and changed the conduction mechanism in polymer.