Electrical breakdown of ethylene-acrylic acid copolymer and blend polymer films

Electrical breakdown of new ethylene copolymers, ethylene-acrylic acid copolymer and its blend polymer, was studied. The DC breakdown strength (F_BDC) of ethylene-acrylic acid copolymer (EAA: 4.6 wt%) was 10.4 MV/cm, which was higher than that of polyethylene homopolymer (PE), 7.4 MV/cm at -60°C. The impulse breakdown strength (F_Blmp) of EAA was also higher than that of PE at -60°C. The increase of F_BDC may be caused by the effect of space charge and/or carrier scattering due to polar groups. The increase in acrylic acid(AA)concentration reduced F_B of EAA. PE and EAA blend polymer (PE+EAA) was prepared for a specimen with a low EAA concentration. All F_B values of (PE+EAA) 4.6 wt% were much lower than those of EAA with the same amount of AA content in the whole temperature region. It was found that F_Blmp of (PE+EAA) 0.1-1 wt% was much higher than F_Blmp of EAA 4.6 wt% at -60°C, while F_BDC of (PE+EAA) 0.1-1 wt% was higher than F_BDC of PE and much lower than F_BDC of EAA at -60°C. Since ethylene and AA functional groups are, respectively, hydrophobic and hydrophilic, EAA copolymer has a bad compatibility with PE. Interfacial defects may be formed between PE phase and EAA phase in PE+EAA blend polymer with a high EAA concentration. The F_B of PE+EAA with a low EAA concentration is high at -60°C since EAA groups act as scattering centers. Therefore, it is effective for the improvement of PE to introduce a low concentration of EAA