Effect of O2/F2/N2 Fluorination on Space Charge Behavior of Low Density Polyethylene

Summary

Two groups of experiments were arranged for our concerned research on oxyfluorination and fluorination of low density polyethylene (LDPE). Original LDPE samples were oxyfluorinated for, respectively, 30 min and 60 min by O2/F2/N2 mixture of 1/1/4 in volume. Then, parts of the oxyfluorinated samples were further fluorinated for another 30 min or 60 min by F2/N2 mixture of 1/4 in volume. All the samples were thin plate about 250 µm in thickness. The space charge characteristics of the samples were tested by using the pulsed electro acoustic (PEA) method. The morphology of the oxyfluorinated and further fluorinated surface layers was characterized by the scanning electron microscope (SEM). Attenuated total reflection infrared (ATR-IR) analyses and X-ray photoelectron spectroscopy (XPS) were adopted to measure the chemical composition of the processed layers. The results reveal that both the process methods obviously change the space charge characteristics of the LDPE samples. The homocharge in the original transforms into heterocharge located near the cathode in the processed samples. Then the heterocharge increases with increase of the oxyfluorination and fluorination duration. The formation of the heterocharges near the cathode can be better explained by the trap level evolution of hole and electron in the surface layer of the processed sample. The oxyfluorination and fluorination processes can break C-H group and introduce CFx (x=1, 2, 3) as well as C=O groups. It changes the microstructure of the surface layer, decreasing the trap level of hole and increasing the trap level of electron. Therefore, hole injection from the anode is enhanced and electron injection from the cathode is weakened. It finally results in the formation of positive heterocharge in processed samples. Besides, the simultaneous introduction of O and F atoms, to some extent, influences the development rate of the polysubstitution strength of H atoms by F atoms.

Additional informations

Authors

Ilisiu, Apetrei, Dragomir