Electrical Properties of LLDPE/LLDPE-g-PS Blends with Carboxylic Acid Functional Groups for Cable Insulation Applications

To improve the electrical properties of linear low-density polyethylene/linear low-density polyethylene-graft-polystyrene (LLDPE/LLDPE-g-PS) blends, carboxylic acid (−COOH) functional polystyrene (PS)-poly(styrene-co-p-acryloyoxybenzoic acid) (P(St-co-ABA)) was prepared by the copolymerization method. The effects of functional PS on the electrical and other properties of LLDPE/LLDPE-g-PS blends were systematically investigated. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results showed the addition of the copolymer had little influence on the crystal form and crystal size but increased the crystallinity degree of LLDPE/LLDPE-g-PS. Compared with LLDPE/LLDPE-g-PS blends, the dielectric constant and the dielectric loss tangent almost had no change. Due to the introduction of a polar group, the breakdown strength of blends was enhanced dramatically with an enhancement of 14.98%. Also, the space charge accumulation was suppressed obviously with a minimum mean volume charge density of 1.35 C/cm3. This supplies a serviceable means to obtain the high voltage direct current (HVDC) cable insulating materials.