Impact of press-molding process on chemical, structural and dielectric properties of insulating polymers

The macroscopic dielectric response of insulating materials, like apparent conductivity or space charge features is known to be sensitive to electrode and interface properties in a general sense. To unravel the detailed properties (chemical, topological, microstructural) controlling electronic properties, specific methods need to be implemented. The present contribution addresses the electrical, as well as the chemical and structural features of low density polyethylene material (LDPE), brought by the use of different protective films during compression moulding. The bare materials were studied by Photoluminescence (PL), Infrared Spectroscopy (IR) and Atomic Force Microscopy to characterize their morphology and chemical properties. Electrical properties were determined by charging/discharging currents and space charge measurements. We show that when using polyethylene terephthalate (PET) as protective cover layer, extra-signatures appear in PL and IR spectra related to diffusion of oxidized groups-presumably decomposition products from PET into the LDPE surface. Also changes in surface roughness appear dependent on the nature of the cover layer. The different press-molding conditions did not reveal substantial changes in the formation of space charge, and the nature of electrode remains the most influencing factor for space charge and conduction features.