Influence of Ungrafted Monomers in Graft Copolymers on Electrical Insulating Properties of Polyethylene

Herein, the effects of ungrafted acrylic acid (AA) monomers in graft copolymers on electrical properties were investigated. Linear low-density polyethylene-grafted AA (LLDPE-g-AA) was synthesized by preirradiation and melt-extrusion grafting. Then, LLDPE/LLDPE-g-AA and LLDPE/u-LLDPE-g-AA blends were prepared based on purified LLDPE-g-AA and untreated LLDPE-g-AA, respectively. The rheological, thermal, and electrical properties of blends were studied and compared. The results showed that the suppression of space charges mainly resulted from grafted polyacrylic acid (PAA) branches. Ungrafted AA monomers in blends had no apparent effects on space charge distribution but featured positive influence on the DC breakdown strength within the concentration range of this study. The dielectric strength for different accelerated migration periods showed that as ungrafted AA monomers migrated from the blends, the influence of ungrafted AA monomers on the dielectric strength weakened, and PAA branches played a dominant role in the enhancement of dielectric strength.