Effects of crystallinity on dielectric properties of poly(L‐lactide)

Poly(L‐lactide) is attracting much attention as a biodegradable polymer. In this paper, effects of crystallinity on dielectric properties of PLLA are discussed. At 80 $C, which is above the glass transition temperature (= about 60 °C), the conductivity increases with a decrease in crystallinity. A thermally stimulated polarization current (TSPC) peak, which seems to be due to segmental‐mode relaxation, appears in all the samples at temperatures around 65 to 70 °C, and it becomes smaller as the crystallinity increases. All the samples show two thermally stimulated depolarization current (TSDC) peaks at around 65 °C and around 90 to 100 °C. The lower‐temperature peak seems to be due to the segmental‐mode relaxation, and the other due to the normal‐mode relaxation. Moreover, all the samples show a drastic increase in the real part of the complex permittivity (εᵣ^ ) and a peak in its imaginary part (ϵr.) at frequencies from 10−1to 104Hz, depending on the measurement temperature. The crystallinity dependencies of the two parts are similar to those of the TSPC and TSDC peaks at around 65 to 70 °C. Therefore, the increase inεᵣ^ and the peak inεᵣ^ are ascribable to the segmental‐mode relaxation.