Kenichi Shinohara

Effect of Carrier Traps in Polyethylene under Gamma‐Ray Irradiation

Stimulated currents are detected with increasing temperature in polyethylene films following the irradiation with high‐energy electron beams at 77°K. A peak current occurs at about 200°K in low‐density specimens and 250°K in high‐density ones.Induced currents I under gamma‐ray irradiation of polyethylene at room temperature depend on dose rate R via I ∝ RΔ. In high‐density polyethylene preirradiation by electron beams of about 5×107 rads at room temperature Δ increases from 0.5 to 0.84 and is accompanied by a decrease of induced current. In the low‐density specimens Δ decreases from 0.8 to 0.6 and the induced current increases with the same preirradiation. After boiling the preirradiated specimen for 5 min, Δ becomes 0.5 in both cases, and in the high‐density specimens the induced current I returns to that of the nonirradiated sample. This behavior suggests that the increase and decrease of carrier traps by these treatments influence the induced current characteristics. Another factor influencing the indu...

E.s.r. study of γ-irradiated isotactic and atactic polypropylene

Abstract An e.s.r. study of γ-irradiated isotactic (i-) and atactic (a-) polypropylene (PP) was carried out. Both the 17 line (or 9 line) spectrum for i-PP and the 6 line spectrum for a-PP are attributed to the tertiary carbon radical, CH 2 C(CH 3 )CH 2 . The difference in the hyperfine structure between the spectrum of i-PP and that of a-PP can be explained by different radical conformations owing to the stereoregularity. Hyperfine coupling and the radical conformation for the tertiary carbon radical in i- and a-PP were determined from the cos 2 ϑ rule. It is shown that the δ methylene proton as well as the β methylene proton contribute to the slight anisotropy in the stretched sample. The spectral change from 9 lines to 17 lines with elevation of temperature, observed at low temperature in i-PP, could be explained by the hindered oscillation of the β methylene proton.

E.s.r. study of u.v.-irradiated polypropylene: effect of the stereoregularity on the behaviour of free radicals produced by u.v. irradiation

Abstract The effect of stereoregularity on the behaviour of free radicals produced in polypropylene by ultra-violet light at low temperature was investigated by an electron spin resonance method. Ultra-violet (u.v.) light is absorbed mainly by carbonyl groups produced in polypropylene by oxidation. The radicals produced at low temperature are identified as CH 2 CH(ĊH 2 )CH 2  and methyl. A large yield of radicals is obtained in samples of poor tacticity. Some of the CH 2 CH(ĊH 2 )CH 2  radicals convert to acyl and some to CH 2 Ċ(CH 3 )CH 2  on warming the sample. The conversion to acyl is remarkable in atactic and stereoblock polypropylene, and that to CH 2 C(CH 3 )CH 2  in isotactic polypropylene. These acyl and CH 2 Ċ(CH 3 )CH 2  radicals return to CH 2 CH(ĊH 2 )CH 2  by illumination, respectively, by visible and u.v. light at 77K. The decay of radicals is attributed to the local motion or microbrownian motion of molecules.

Comparison between electrical conduction in polyethylene under gamma irradiation and without irradiation

Some of the phenomena of electrical conduction in polyethylene, as observed in this study, are: voltage-current curves; temperature-dependence of conductivity; and the effect of environment on the magnitude of conductivity in air, in vacuum, and in silicone oil.