Effects of crystallinity on dielectric properties of poly (1-lactide)

Poly (L-lactide) (PLLA) is attracting much attention as a biodegradable polymer. In this paper, effects of crystallinity on dielectric properties of PLLA are studied. 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, while the other due to the normal-mode relaxation. Moreover, all the samples show a drastic increase in the real part of complex permittivity (ε ^r') and a peak in its imaginary part (ε ^r,") at frequencies from 10 ^-1 to 10 ⁴ Hz, depending on the measurement temperature. The crystallinity dependencies of the two parts are similar to those of the TSPC and TSDC peaks around 65 to 70 °C. Therefore, the increase in ε ^r and the peak in ε ^r are ascribable to the segmental-mode relaxation.