Electrical degradation of blends and laminar composites of polyethylene and polystyrene

Physical blends and laminar composites of polystyrene (PS) and polyethylene (PE) were prepared with and without a tri-block copolymer compatibilizer (poly(styrene-block-(ethylene-co-1-butene)-block-styrene)), denoted SEBS. Dielectric strength and breakdown time of samples exposed to external partial discharges (PD) were measured and relationships were sought with composition, phase morphology, and phase bonding. The polymers were selected because they are incompatible and because the dielectric strength and stability towards PD are greater for PS than for PE. It was shown by adding small quantities of SEBS that a minimum amount of cohesive forces between the components was required to achieve good electrical properties. The major morphological factor controlling the electrical stability was which polymer constituted the continuous phase. Laminar composites with continuous sheets of stable PS as a top layer exhibited a stability equal to or better than that predicted from the upper bound rule of mixing.