CHARGE TRAPPING AND CONDUCTION IN PURE AND IODINE-DOPED BIAXIALLY-ORIENTED POLYPROPYLENE

Study of charge trapping and conduction in pure and iodine doped biaxi ally oriented polypropylene (BOPP) is presented. Structural and chemic al modifications induced by iodine were investigated using X-ray, opti cal and infrared methods. Optical spectra of doped BOPP show absorptio n at 290 nm from charge transfer complexes. X-ray examination revealed a decrease in crystallinity and crystallite size after doping. Effect of iodine on charge trapping was determined by thermally stimulated c urrent technique. Deep traps (120-degrees-C peak) at crystalline-amorp hous interfaces are destroyed by iodine, which provides new traps (68- degrees-C peak) with activation energy 0.9 eV. Pressure dependence of conductivity indicates ionic conduction in pure samples and electronic conduction in doped samples. Steady state currents in 0.5 %wt iodine doped BOPP were measured for fields 1 to 5x10(5) V cm-1 and at elevate d temperatures 22 to 50-degrees-C. Iodine enhances conductivity by app roximately 700x in pure BOPP and the steady state conductivity shows g ood fit of the 3-d Poole-Frenkel theory to the experiment. It is propo sed that trapped electrons (arising due to donor-acceptor action) ther mally released through PF lowering, predominantly contribute to the co nduction.