Effect of glass transition on conduction current in biodegradable poly-L-lactic acid [electrical insulation]

The temperature dependence of electrical conduction current in additive-free poly-L-lactic acid was measured. Although the current obeys the Arrhenius formula, a hump appears under some conditions, depending on whether the temperature is being ascended or descended, and also on whether the sample was poled or short-circuited prior to the measurements. That polar groups consisting mainly of carbonyl groups in the sample changed their directions was confirmed by Fourier-transform infrared spectroscopy. The permittivity increases around 74°C. From these results, it is confirmed that orientational polarization or depolarization occurs around 74°C by the glass transition, and that its resultant current and the conduction current overlap with each other.