Effect of Crystallinity on Electrical Conduction Characteristics of Poly-L-lactic Acid

Effect of crystallinity change on electrical conduction characteristics of poly-L-lactic acid was studied experimentally. The crystallinity was changed by thermal annealing. The lower crystallinity samples have more remaining charge than the higher crystallinity samples. Moreover, at 80 degC that is above their glass transition temperatures (T_g: 55-60 degC), the conductivity is much higher in the lower crystallinity sample than in the higher crystallinity sample. The low crystallinity sample shows two thermally stimulated current (TSC) peaks - one around T_g and the other at a temperature about 20 degC higher than T_g, while the higher crystallinity sample shows only the lower-temperature TSC peak. The TSC peak around T_g is attributable to the micro-Brownian motion that enables orientation of dipoles having the direction perpendicular to the polymer main chains, while the higher-temperature TSC peak seems attributable to the orientation and magnitude change of the end-to-end vector in the polymer main chain.