Space charge behavior in LDPE and its blend polymers

The space charge behaviors in LDPE and blend polymers of LDPE and random copolymer of ethylene and propylene (EP) were investigated with the pulsed electro-acoustic (PEA) method. A positive DC voltage was applied to the semiconductive electrode of Al/specimen/semiconductive layer. The blend specimen of 90 wt.% LDPE and 10 wt.% polypropylene copolymer (B10) showed more space charge than pure LDPE (PE) under a DC field of 50 MV m^-1 at both 30 and 60°C. Positive space charge moved more slowly in B10 than in PE at 30°C. DC current of B10 was less than that of PE at 30°C, but higher at 60°C. The decay characteristics of space charge after short-circuiting were also investigated. The decay processes for both PE and B10 had two time constants which suggest the existence of two kinds of carrier traps. The activation energy was estimated from the temperature dependence of decay time constant. The activation energy corresponding to trap depth increased by blending polypropylene copolymer with LDPE, suggesting the modification of traps by blending.